MX2007001475A

MX2007001475A - Stacked organic photosensitive devices

Info

Publication number: MX2007001475A
Application number: MXMX/A/2007/001475A
Authority: MX
Inventors: Xue Jiangeng; Uchida Soichi; Forrest Stephen; P Rand Barry
Original assignee: The Trustees Of Princeton University
Priority date: 2004-08-05
Filing date: 2007-02-02
Publication date: 2008-10-03

Abstract

A device is provided having a first electrode, a second electrode, a first photoactive region having a characteristic absorption wavelengthÎ»1 and a second photoactive region having a characteristic absorption wavelengthÎ»2. The photoactive regions are disposed between the first and second electrodes, and further positioned on the same side of a reflective layer, such that the first photoactive region is closer to the reflective layer than the second photoactive region. The materials comprising the photoactive regions may be selected such thatÎ»1 is at least about 10%different fromÎ»2. The device may further comprise an exciton blocking layer disposed adjacent to and in direct contact with the organic acceptor material of each photoactive region, wherein the LUMO of each exciton blocking layer other than that closest to the cathode is not more than about 0.3 eV greater than the LUMO of the acceptor material.

Description

STACKED ORGANIC PHOTOSENSIBLE DEVICES Field of the Invention The present invention relates in general to organic photosensitive optoelectronic devices. More specifically, it relates to organic photosensitive optoelectronic devices that have higher efficiency.

Background of the Invention Optoelectronic devices are based on the optical and electronic properties of materials to produce or detect electromagnetic radiation in electronic form or to generate electricity from ambient electromagnetic radiation.

Photosensitive optoelectronic devices convert electromagnetic radiation into electricity. Solar cells, also called photovoltaic (PV) devices, are a type of photosensitive optoelectronic device that is specifically used to generate electrical energy. PV devices, which can generate electrical power from light sources other than sunlight, can be used to drive loads that consume energy to provide, for example, lighting, heating or to power circuits or electronic devices such as calculators, radios, computers or monitoring equipment or remote communications. These power generation applications often also consist of charging batteries or other devices for energy storage so that operation can continue when direct illumination from the sun or from other sources of ambient light no longer exists, or Balance the output of the PV device with specific application requirements. As used herein the term "resistive load" refers to any circuit, device, equipment or system for energy consumption or storage.

Another type of photosensitive optoelectronic device is a photoconductive cell. In this function, a signal detection circuit monitors the resistance of the device to detect changes due to the absorption of light.

Another type of photosensitive optoelectronic device is a photodetector. In operation a photodetector is used in conjunction with a current detection circuit that measures the current that is generated when the photodetector is exposed to electromagnetic radiation and may have a voltage of applied polarization. A detector circuit described herein is capable of providing polarization voltage to a photodetector and of measuring the electronic response of the photodetector to electromagnetic radiation.

These three classes of photosensitive optoelectronic devices can be characterized according to whether a rectifying junction defined below is present and also according to whether the device is operated with an external applied voltage, also called polarization or polarization voltage. A photoconducting cell does not have a rectifying junction and is usually operated with a polarization. A PV device has at least one rectifying junction and is operated without any polarization. A photodetector has at least one rectifier junction and generally but not always with a polarization. As a general rule, a photovoltaic cell provides power to a circuit, device or equipment, but does not provide a signal or current to control the detection circuit, or the output of information from the detection circuit. In contrast, a photodetector or photoconductor provides a signal or current to control the detection circuit, or the output of information from the detection circuit but does not provide power to the circuit, device or equipment.

Traditionally, photosensitive optoelectronic devices have been constructed of numerous inorganic semiconductors, for example, crystalline, polycrystalline and amorphous silicon, gallium arsenide, cadmium telluride and others. Here, the term "semiconductor" indicates materials that conduct electricity when the charge carriers are induced by thermal or electromagnetic excitation. The term "photoconductor" is generally related to the process in which the electromagnetic radiant energy is absorbed and thus converted into excitation energy of the electric charge carriers in such a way that the carriers can drive, that is to say, to transport the electric charge in a material. The terms "photoconductor" and "photoconductive material" are used herein to refer to semiconductor materials that are chosen because of their property of absorbing electromagnetic radiation to generate electric charge carriers.

PV devices can be characterized by the efficiency with which they convert incident solar energy into useful electrical energy. Devices that use crystalline or amorphous silicon dominate commercial applications and some have achieved efficiencies of 23% or more. However, efficient crystalline-based devices, especially of large surface area, are difficult and expensive to produce due to the problems inherent in the production of large crystals without defects that degrade the efficiency significantly. On the other hand, high efficiency amorphous silicon devices still have problems with stability. Amorphous silicon cells commercially available today have stabilized efficiencies of between 4% and 8%. The most recent efforts have focused on the use of organic photovoltaic cells to achieve acceptable photovoltaic conversion efficiencies with economical production costs.

The PV devices are optimized for the generation of maximum electric power under standard lighting conditions (ie, Standard Test Conditions that are 1000 W / m2, spectral illumination of AM1.5), for the maximum product of the photoelectric current by the photoelectric voltage. The energy conversion efficiency of that cell under standard lighting conditions depends on the following three parameters: (1) the current under zero polarization, ie short-circuit current IScr (2) the photoelectric voltage in open-circuit conditions, ie , the open circuit voltage Voc and (3) the load factor, ff.

PV devices produce a photo-generated current when they are connected through a load and irradiated with light. When it is radiated under an infinite charge, a PV device generates its maximum possible voltage, V open circuit, or V0o If it is irradiated with its electrical contacts in short circuit, a PV device generates its maximum possible current, I short circuit, or Isc. When it is actually used to generate power, a PV device is connected to a finite resistive load and the energy output is given by the product of current and voltage, I x V. The maximum total energy generated by a PV device is implicitly unable to exceed the product, Isc x Voc. When the load value is optimized for maximum energy extraction, the current and voltage have the values, Imzx and Vmzx, respectively.

A merit figure for PV devices is the load factor, ff, which is defined as: where ff is always less than l, since ISc and Voc are never obtained simultaneously in actual use. Anyway, when ff approaches l, the device has less resistance in series or internal and therefore supplies a greater percentage of the product of Isc and V0c to the load under optimal conditions. When Pinc is the energy incident on the device, the energy efficiency of the device, ??, can be calculated by: When the electromagnetic radiation of an appropriate energy is incident on an organic semiconductor material, for example, an organic molecular crystalline material (OMC), or a polymer, a photon can be absorbed to produce a molecular state excited. This is represented symbolically as ¾ + ??? So * _ Here, S0 and So * indicate the molecular states of ground connection and excited, respectively. The absorption of energy is associated with the promotion of an electron from a state linked to the HOMO energy level, which can be a ligature of p, to the energy level LÜMO, which can be a ligature ap *, or in an equivalent way, the promotion of a hollow of the energy level LÜMO to the energy level HOMO. In thin-film organic photoconductors, it is generally believed that the generated molecular state is an exciton, that is, an electron-hole pair in a bound state that is transported as a quasiparticle. The excitons can have an appreciable duration before the geminated recombination, which refers to the recombination process of the original electron and the gap with one another, as opposed to the recombination with holes or electrons of other pairs. To produce a photoelectric current, the pair The electron-hole must be separated, usually in a donor-acceptor interconnection between two thin dissimilar organic contact films. If the charges do not separate, they can recombine in a process of recombination geminante, also called interruption, either in radiative form, through the emission of light of a lower energy than the incident light, or in non-radiative form, through the production of heat. Any of these results is undesirable in a photosensitive optoelectronic device.

Electrical fields or inhomogeneities in a contact can cause an exciton to be interrupted instead of dissociating in the donor-acceptor interconnection, which results in no net contribution to the current. Accordingly, it is desirable to keep the photogenerated excitons away from the contacts. This has the effect of limiting the diffusion of the excitons to the region near the junction such that the associated electric field has an opportunity to separate the charge carriers released by the dissociation of the excitons near the junction.

To produce internally generated electric fields that occupy a substantial volume, the usual method is to juxtapose two layers of material with appropriately selected conductive properties, especially with respect to their distribution of molecular quantum energy states. The interconnection of these two materials is called a photovoltaic heterojunction. In the theory of traditional semiconductors, it has been indicated that the materials for forming PV heterojunctions are generally of the n or p type. Here, type n indicates that the type of major carrier is the electron. This can be seen as the material that has many electrons in relatively free energy states. The type p indicates that the type of majority carrier is the hole. That material has many gaps in relatively free energy states. The type of the background, that is, the concentration of the non-photogenerated majority carrier, depends mainly on an involuntary interruption due to defects or impurities. The type and concentration of impurities determine the value or level of Fermi energy within the space between the highest occupied molecular orbital energy level (HOMO) and the lowest unoccupied molecular orbital energy level (LUMO), termed HOMO-LÜMO space. The Fermi energy characterizes the statistical occupation of the states of molecular quantum energy indicated by the energy value for which the probability of occupancy is equivalent to ½. A Fermi energy close to the LÜMO energy level indicates that the electrons are the predominant carrier. A Fermi energy close to the HOMO energy level indicates that the gaps are the predominant carrier. Therefore, the Fermi energy is the property of The main characterization of traditional semiconductors and the phototipic PV heterojunction has traditionally been the p-n interconnection.

The term "rectifier" indicates, among others, that an interconnection has an asymmetric conduction characteristic, that is to say the interconnection supports the electronic load transport preferably in. one direction. Rectification is normally associated with a built-in electric field that occurs in the heterojunction between appropriately selected materials.

As used herein, and as generally understood by one skilled in the art, a first energy level "Highest Occupied Molecular Orbital" (HOMO) or "Lowest Unoccupied Molecular Orbital" (LOMO) is "greater than" or " higher than "a second energy level HOMO or LUMO if the first energy level is closer to the vacuum energy level. Since ionization potentials (IP) are measured as a negative energy in relation to a vacuum level, a higher HOMO energy level corresponds to an IP that has a lower absolute value (an IP that is less negative). Similarly, a higher LUMO energy level corresponds to an electron affinity (AE) that has a lower absolute value (an AE that is less negative). In an energy level diagram conventional, with the vacuum level up, the LUMO energy level of a material is higher than the HOMO energy level of the same material. A higher "HOMO" or "LUMO" energy level seems closer to the top of that diagram than a "lower" HOMO or LUMO energy level.

In the context of organic materials, the terms "donor" and "acceptor" refer to the relative positions of the HOMO and LUMO energy levels of two organic materials in contact but different. This differs from the use of these terms in the inorganic context, where "donor" and "acceptor" can refer to types of switches that can be used to create layers of types n and p, respectively. In the organic context, if the LUMO energy level of a material in contact with another is smaller, then that material is an acceptor. Otherwise it is a donor. It is energetically favorable, in the absence of an external polarization, that electrons in a donor and acceptor link move in the acceptor material, and that the voids move in the donor material.

A significant property in organic semiconductors is the mobility of the carrier. Mobility measures the ease with which a load carrier can move through a conductive material in response to an electric field. In the context of Organic photosensitive devices, a layer that includes a material that preferentially conducts electrons due to high electron mobility can be termed electron transport layer, or ETL. A layer that includes a material that preferentially conducts voids due to a high mobility of the voids can be referred to as a void transport layer, or HTL. Preferably, but not necessarily, an acceptor material is an ETL and a donor material is an HTL.

Conventional inorganic semiconductor PV cells employ a union of p and n to create an internal field. The first thin-layer organic cells, such as those reported by Tang et al, Appl. Phys. Lett. 48, 183 (1986), contain a heterojunction analogous to that used in a conventional inorganic PV cell. However, it is now recognized that in addition to the establishment of a p and n type union, the deviation of the energy level of the heterojunction also plays an important role.

It is believed that the deviation of the energy level in the organic D-A heterojunction is important for the operation of organic PV devices due to the fundamental nature of the photogeneration process in organic materials. When the optical excitation of an organic material occurs, excitons are generated of Frenkel or localized load transfer. For electrical detection or current generation to occur, the bound excitons must dissociate in their constituent electrons and holes. This process can be induced by the built-in electric field, but the efficiency in the electric fields that is generally found in the organic devices (F 106 V / cm) is low. The most efficient exciton dissociation in organic materials occurs in a donor-acceptor (D-A) interconnect. In this interconnection, the donor material with a low ionization potential forms a heterojunction with an acceptor material with a high electron affinity. According to the alignment of the energy levels of the donor and acceptor materials, the excitation of the exciton can be made energetically favorable in that interconnection, leading to a free electron polaron in an acceptor material and a free-space polaron in the donor material.

Organic PV cells have many potential advantages when compared to traditional silicon-based devices. Organic PV cells are lightweight, economical in the use of materials, and can be deposited on low cost substrates, such as flexible plastic sheets. However, some organic PV devices generally have a relatively low external quantum efficiency, which is the order of 1% or less. It is thought that this is due, in part, to the second-order nature of the intrinsic photoconductive process. That is, the generation of the carrier requires the generation, diffusion and ionization or collection of excitons. Is there an efficiency? associated with each of these processes. The following subscripts can be used: P for energy efficiency, EXT for external quantum efficiency, A for photon absorption, ED for diffusion, CC for charge collection and INT for internal quantum efficiency. Using this notation: The diffusion length (LD) of an exciton is generally much smaller (LD 50 A) than the optical absorption length (500 A), which requires an intermediate point between using a thick cell, and consequently resistive, with several interconnections or highly folded interconnections, or a thin cell with low optical absorption efficiency.

Generally, when light is absorbed to form an exciton in an organic thin film, a singlet exciton is formed. Through the intersystem crossing mechanism, the singlet exciton can decay to a triplet exciton. In this process, energy is lost, which results in a lower efficiency for the device. If it were not for the loss of energy from the intersystem crossing, it would be desirable to use materials that generate triplet excitons, since the triplet excitons generally have a longer duration, and consequently a longer diffusion length, than the excitons of triplet. singlet Extract of the Invention A device is provided having a first electrode, a second electrode, a first photoactive region having a characteristic absorption wavelength ?? and a second photoactive region having a characteristic wavelength? 2. The photoactive regions are disposed between the first and second electrodes, and furthermore they are located on the same side of a reflective layer, in such a way that the first photoactive region is closer than the reflective layer than the second photoactive layer. The materials comprising the photoactive regions can be selected such that ?? is at least 10% different from? 2. The device may further comprise an exciton blocking layer disposed adjacent to and in direct contact with the organic acceptor material of each photoactive region, wherein the LUMO of each exciton blocking layer different from the which is closer to the cathode is no more than 0.3 eV greater than the LUMO of the acceptor material.

Brief Description of the Drawings Figure 1 shows an organic PV device comprising an anode, an anode smoothing layer, a donor layer, an acceptor layer, a blocking layer and a cathode.

Figure 2 shows an organic tandem device that is formed by stacking two cells in series.

Figure 3 shows the intensities of the optical field a? = 450 nm (full line) and? = 650 nm (dotted line) as a function of the distance from the cathode in the asymmetric organic tandem cell B (see Table I), whose structure is shown schematically in the upper part of Figure 3.

Figure 4 shows the external quantum efficiency spectra calculated for the frontal cell (dotted line) and the posterior cell (filled line) of the B cell.

Figure 5 shows the characteristics of current density as a function of the voltage (J-V) of the asymmetric organic tandem cell A, in the dark and under different intensities of AM1.5G solar illumination.

Figure 6 shows the dependence of illumination intensity (P0) with respect to the energy conversion efficiencies (??) of asymmetric organic tandem cells (A, full squares; B, open circles; C, full triangles) under AM1.5G stimulated solar illumination, compared to those of 5% of a hybrid mixed planar heterojunction cell of CuPc / C6o (open inverted triangles).

Figure 7 shows the load factor (FF) of the tandem and unique hybrid PM-HJ cells shown in Figure 6.

Figure 8 shows two possible geometries of a PV device with representative perpendicular optical path lengths.

Figure 9 shows absorption spectra of CuPc / C6o films with different mixing ratios, deposited in ITO.

Detailed description of the invention An organic photosensitive optoelectronic device * is provided. The organic devices of embodiments of the present invention can be used, for example, to generate an electrical current usable from incident electromagnetic radiation (e.g., PV devices) or can be used to detect incident electromagnetic radiation. The embodiments of the present invention may comprise an anode, a cathode and a photoactive region between the anode and the cathode. The photoactive region is the part of the photosensitive device that absorbs electromagnetic radiation to generate excitons that can be dissociated to generate electric current. The photosensitive optoelectronic devices may also include at least one transparent electrode to allow incident radiation to be absorbed by the device. Various materials and configurations of PV devices are described in U.S. Patent Nos. 6,637,378, 6,580,027 and 6,352,777, which are incorporated herein by reference in their entirety.

Figure 1 shows an organic photosensitive optoelectronic device 100. The figures are not necessarily drawn in scale. The device 100 may include a substrate 110, a anode 115, an anode aliquot layer 120, a donor layer 125, an acceptor layer 130, a blocking layer 135, and a cathode 140. The cathode 140 can be a composite cathode having a first conductive layer and a second conductive layer. The device 100 can be manufactured by depositing the layers described, in order. The charge separation can occur predominantly in the organic heterojunction between the donor layer 125 and the acceptor layer 130. The potential incorporated in the heterojunction is determined by the difference in energy level HOMO-LUMO between the two materials that come in contact to form the heterojunction. The deviation of the HOMO-LUMO space between the donor and acceptor materials produces an electric field in the donor and acceptor interconnection that facilitates the charge separation for the excitons created within the diffusion length of excitons of the interconnection.

The specific arrangement of the layers illustrated in Figure 1 is an example only, and it is not desired to limit it. For example, some of the layers (such as blocking layers) can be omitted. Other layers can be added (such as reflecting layers or additional acceptor and donor layers). The order of the layers can be altered. Arrangements other than those specifically described may be used.

The substrate can be any suitable substrate that provides desired structural properties. The substrate can be flexible or rigid, planar or non-planar. The substrate can be transparent, translucent or opaque. Plastic and glass are examples of preferred rigid materials of the substrate. Plastic and metal sheets are examples of preferred flexible substrate materials. The material and the thickness of the substrate can be chosen to obtain desired structural and optical properties.

U.S. Patent 6,352,777, incorporated herein by reference, provides examples of electrodes, or contacts, that may be used in a photosensitive optoelectronic device. When used herein, the terms "electrode" 'and "contact" refer to layers that provide a means for supplying photogenerated current to an external circuit or providing a polarization voltage to the device. That is, an electrode, or contact, provides the interconnection between the active regions of an organic photosensitive optoelectronic device and a cable, conductor, line or other means for transporting the charge carriers to or from the external circuit. In a photosensitive optoelectronic device, it is desirable to allow the maximum amount of ambient electromagnetic radiation from the exterior of the device to be admitted to the inner photoconductive active region. That is, electromagnetic radiation it must reach a photoconductive layer, where it can be converted into electricity by photoconductive absorption. This often indicates that at least one of the electrical contacts must absorb minimally and reflect minimally the incident electromagnetic radiation. That is, that contact must be substantially transparent. The opposite electrode can be a reflective material so that light that has passed through the cell without being absorbed is reflected back through the cell. As used herein, it is said that a layer of the material or a sequence of several layers of different materials is "transparent" when the layer or layers allow at least 50% of the ambient electromagnetic radiation at relevant wavelengths to be transmitted to through the layer or layers. Similarly, layers that allow something less than 50% of the transmission of ambient electromagnetic radiation at relevant wavelengths are said to be "semitransparent".

As used herein, "upper" means the furthest from the substrate, while "lower" means the closest to the substrate. For example, for a device having two electrodes, the lower electrode is the electrode closest to the substrate, and is generally the electrode that is first manufactured. The lower electrode has two surfaces, one surface bottom closest to the substrate and an upper surface furthest away from the substrate. When a first layer is described as "disposed on" a second layer, the first layer is disposed further away from the substrate. There may be other layers between the first and the second layer, unless it is specified that the first layer is "in physical contact with" the second layer. For example, a cathode can be described as "disposed on" an anode, even when there are several organic layers between them.

The electrodes are preferably composed of metals or "metal substitutes". Here the term "metal" is used to encompass both the materials composed of an elementally pure metal, for example, Mg, and alloys of metals that are composite materials two or more elementally pure metals, for example Mg and Ag together, indicated Mg: Ag. Here, the term "metal substitute" refers to a material that is not a metal within the normal definition, but that has the metal-like properties that are desired in certain appropriate applications. Metal substitutes commonly used for electrodes and charge transfer layers include interrupted broadband space semiconductors, for example, transparent conductive oxides such as indium tin oxide (ITO), gallium oxide, indium and tin (GITO). and indium zinc oxide and tin (ZITO). In particular, ITO is a highly degenerate n + degenerate semiconductor with an optical band gap of 3.2 eV, which makes it transparent at wavelengths greater than 3900 A. Another suitable metal substrate is transparent conductive polymer polyaniline (PA I) and its chemical relatives. Metal substrates can also be "selected from a wide range of non-metallic materials, where the term" non-metallic "is understood to encompass a wide range of materials as long as the material does not contain metal in its non-chemically combined form. Metal is present in its non-chemically combined form, alone or in combination with another or other metals such as an alloy, it can be said that the metal is present in its metallic form or is a "free metal". Metal substitutes of the present invention can sometimes be referred to as "metal-free" wherein the term "metal-free" expressly means that it encompasses an all-metal material in its non-chemically combined form.The free metals generally have a metal bonding form that is derived of numerous electrons that are free to move in an electronic conduction band throughout the metal network, although metal substitutes may contain The constituents of metals are "non-metallic" on several bases. They are not pure free metals nor are alloys of free metals. When metals are present in their metallic form, the electronic conduction band tends to provide, among others metallic properties, high electrical conductivity as well as high reflection for optical radiation.

The embodiments of the present invention may include, as one or more of the transparent electrodes of the photosensitive optoelectronic device, a low-resistance, non-metallic, highly transparent cathode as described in US Pat. No. 6,420,031 to Parthasarathy et al. ("Parthasarathy? 031"), or a highly efficient, low strength metal / non-metallic composite cathode such as that disclosed in US Patent No. 5,703,436 to Forrest et al ("Forrest et al 36"), both incorporated here as a reference in its entirety. Each type of cathode is preferably prepared in a manufacturing process that includes the step of sputtering deposition of an ITO layer onto an organic material, such as copper phthalocyanine (CuPc), to form a low strength, non-metallic cathode, Highly transparent or on a layer of Mg: Ag thin to form a cathode of metal / non-metallic compound of low resistance, highly efficient.

Here, the term "cathode" is used in the following way. In a non-stacked PV device or a single unit of a PV device stacked under ambient irradiation and connected to a load resistive and with no voltage applied externally, for example, a PV device, the electrons move towards the cathode from the photoconductive material. Similarly, the term "anode" is used here in such a way that in a PV device under illumination, the voids move towards the anode from the photoconductive material, which is equivalent to the electrons moving in the opposite form. It is noted that as used- these terms, anodes and cathodes may be electrodes or load transfer layers.

An organic photosensitive device comprises at least one photoactive region in which the light is absorbed to form an excited state, or "exciton", which can later be dissociated into an electron and a gap. Exciton dissociation generally occurs in the heterojunction formed by the juxtaposition of an acceptor layer and a donor layer. For example, in the device of Figure 1, the "photoactive region" may include donor layer 125 and acceptor layer 130.

The acceptor material may be composed, for example, of perylenes, naphthalenes, fullerenes or nanotubules. An example of an acceptor material is bis-benzynamidozol · 3,4,9,10-perylentetracarboxylic acid (PTCBI). Alternatively, the acceptor layer may be composed of a fullerene material such as described in U.S. Patent No. 6,580,027, incorporated herein by reference in its entirety. Adjacent to the acceptor layer is a layer of organic donor type material. The limit of the acceptor layer and the donor layer form the heterojunction that can produce an internally generated electric field. The material for the donor layer can be a phthalocyanine or a porphyrin, or a derivative or transition metal complex thereof, such as copper phthalocyanine (CuPc). Other suitable acceptor and donor materials may be used.

Using an organometallic material in the photosensitive region, devices incorporating these materials can utilize triplet excitons. It is believed that the singlet and triplet mixture can be so resistant to organometallic compounds that the absorptions consist of the excitation from the singlet grounding states directly to the excited triplet states, eliminating the losses associated with the conversion of the excited state from singlet to triplet excited state. The longer duration and diffusion length of the triplet excitons compared to the singlet excitons may allow the use of a thicker photoactive region, since the triplet excitons may diffuse a greater distance to arrive at the heterojunction of donor and acceptor, without sacrificing the efficiency of the device.

It is also possible to use materials other than organometallics.

In a preferred embodiment of the invention, the stacked organic layers include one or more exciton blocking layers (EBL) which are described in U.S. Patent No. 6,097,147, Peumans et al, Applied Physics Letters 2000, 76, 2650- 52, and the pending patent application number 09 / 449,801, filed on November 26, 1999, both incorporated herein by reference. Higher internal and external quantum efficiencies have been achieved including an EBL to confine the photogenerated excitons to the region near the dissociation interconnection and to prevent the cooling of parasitic excitons in the photosensitive electrode / organic interconnection. In addition to limiting the volume over which the excitons can be diffused, an EBL can also act as a diffusion barrier for substances introduced during the deposition of the electrodes. In some circumstances, an EBL can be made thick enough to fill stings or short circuit defects that may otherwise render an organic PV de nonfunctional. An EBL can consequently help to protect fragile organic layers from the damage produced when the electrodes are deposited in organic materials.

It is believed that the EBLs obtain their exciton blocking property from having a LUMO-HOMO energy space substantially larger than that of the adjacent organic semiconductor from which the excitons are being blocked. Therefore, excitons confined to the EBL are prohibited due to energy considerations. While it is desirable for the EBL to block excitons, it is not desirable for the EBL to block the entire load. However, due to the nature of the adjacent energy levels, an EBL can block a sign of the load carrier. By its design, an EBL can be between two other layers, generally a photosensitive organic semiconductor layer and an electrode or a charge transfer layer. The electrode or the charge transfer layer is in the context of a cathode or an anode. Accordingly, the material for an EBL at a given position in a de is chosen such that the desired sign of the carrier is not prevented in its transport towards the electrode or the load transfer layer. The alignment of the correct energy level guarantees that there is no barrier to the transport of cargo, preventing an increase in series resistance. For example, it is desirable that a material used as a lateral EBL of the cathode have a LUMO energy level closely equal to the LÜMO energy level of the adjacent ETL material such that any undesired barrier to the electrons is minimized.

It should be appreciated that the exciton-blocking nature of a material is not an intrinsic property of its HOMO-LUMO energy space. Whether a given material acts as an exciton blocker depends on the relative HOMO and LUMO energy levels of the adjacent photosensitive organic material. Accordingly, it is not possible to identify a class of isolated compounds as excitone blockers without taking into account the context of the de in which they can be used. However, with the teachings herein an artisan can identify whether a given material functions as an exciton blocking layer when used with a selected set of materials to construct an organic PV de.

In a preferred embodiment of the invention, an EBL is located between the acceptor layer and the cathode, a preferred material for EBL comprises 2,9-dimethyl-4,7-diphenyl-1, 10-phenanthridine (also called batocuproin or BCP), which is believed to have a LUMO-HOMO energy level separation of 3.5 eV, or bis (2-methyl-8-hydroxyquinolinoate) -aluminium (III) phenolate (Alq20PH). BCP is an effective exciton blocker that can easily transport electrons to the cathode from an acceptor layer.

The EBL layer can be interrupted by a single switch, which includes, but is not limited to, 3,4,9,10-perylentetracarboxylic dianhydride (PTCDA), 3,4,9,10-perylentetracarboxylic diimide (PTCDI), 3, 4, 9, 10-perylentetracarboxylic bis-benzimidazole (PTCBI), 1,4,5,8-naphthaletracarboxylic dianhydride (NTCDA), and derivatives thereof. It is thought that the BCP. deposited in the present devices is amorphous. The present blocking layers of amorphous BCP excitons may exhibit recrystallization of the film, which is especially rapid under high light intensities. The morphology change resulting from the polycrystalline material results in a lower quality film with possible defects such as short circuits, gaps or intrusion of the electrode material. Accordingly, it has been discovered that the disruption of some EBL materials, such as BCP, which exhibit this effect with a relatively large and stable, suitable molecule can stabilize the structure of the EBL to prevent morphological changes that degrade performance. It should also be noted that the interruption of an EBL that carries electrons in a given device with a material having a LUMO energy level close to that of the EBL helps to ensure that no electron traps are formed that can result in charge formation of space and reduce performance. In addition, it should be noted that the relatively low interruption densities they must minimize the generation of excitons at isolated breakpoints. Since excitons are effectively prohibited from spreading surrounding the EBL material, these absorptions reduce the photoconversion efficiency of the device.

Representative embodiments may also comprise load transfer layers or charge recombination layers. As described herein, the charge transfer layers are distinguished from the acceptor and donor layers by the fact that the charge transfer layers are frequently, but not necessarily, inorganic (often metals) and can be chosen so that they do not are active in photoconductive form. The term "charge transfer layer" is used herein to refer to similar but different layers of the electrodes in that the charge transfer layer only supplies charge carriers from a subsection of an optoelectronic device to the adjacent subsection. The term "charge recombination layer" is used herein to refer to similar but different layers of the electrodes in that a charge recombination layer for the recombination of electrons and gaps between photosensitive devices in tandem and may also increase the resistance of the internal optical field near one or more active layers. A layer of charge recombination can constructed of nanoparticles, nanoparticles, or semitransparent metal nanobords that are described in U.S. Patent No. 6,657,378 incorporated herein by reference in its entirety.

In a preferred embodiment of the invention, an anode smoothing layer is located between the anode and the donor layer. A preferred material for this layer comprises a film of 3,4-polyethylenedioxythiophene: polystyrene sulfonate (PEDOT: PSS). The introduction of the PEDOT: PSS layer between the anode (ITO) and the donor layer (CuPc) can result in greatly improved manufacturing yields. This is attributed to the ability of the PEDOT: PSS film coated with spin to plan the ITO, whose rough surface can otherwise short-circuit through the thin molecular layers.

In another embodiment of the invention, one or more of the layers can be treated with plasma before depositing the next layer. The layers can be treated, for example, with an argon plasma or mild oxygen. This treatment is beneficial since it reduces the resistance in series. It is particularly advantageous if the PEDOTrPSS layer is subjected to a mild plasma treatment before the deposition of the next layer.

The simple layer structure illustrated in Figure 1 is provided by way of non-limiting example, and it is understood that the embodiments of the invention may be used in connection with a wide variety of other structures. The specific materials and structures described are examples and other materials and structures can be used. Functional devices can be made by combining the different layers described in different ways, or the layers can be omitted absolutely, based on design, performance and cost factors. Other layers that are not specifically described may also be included. Materials other than those specifically described may be used. Although many of the examples given herein describe different layers comprising a single material, it is understood that combinations of materials may be used, such as a mixture of guest and switch, or more generally a mixture. Also the layers may have different sublayers. The names given to the different layers here are not included to be strictly exhaustive. Organic layers that are not part of the photoactive region, that is to say organic layers that do not generally absorb photons that make an important contribution to the photoelectric current, can be called "non-photoactive layers". Examples of non-photoactive layers include EBL and smoothing layers of anodes. Other types of non-photoactive layers can also be used.

Preferred organic materials for use in the photoactive layers of a photosensitive device include photosensitized organometallic compounds. The term "organometallic" as used herein is as generally understood by an expert in the art and is given, for example, in "Inorganic Chemistry" (2nd edition) by Gary L. Miessler and Donald A. Tarr, Prentice Hall (1998). Therefore, the term "organometallic" refers to compounds that have an organic group bonded to a metal through a carbon-metal bond. This class does not itself include coordination compounds, which are substances that have any donor bond from the heteroatoms, such as amine complexes, halides, pseudohalides (CN, etc.) and the like. In practice, organometallic compounds generally comprise, in addition to one or more carbon-metal bonds to an organic species, one or more donor bonds from a heteroatom. The carbon-metal bond to an organic species refers to a direct bond between a metal and a carbon atom of an organic group, such as phenyl, alkyl, alkenyl, etc. but it does not refer to a metal bond to an "inorganic carbon", such as the carbon of CN or CO. The term "cyclometalized" refers to compounds comprising a bidentate organometallic ligand such that, when bound to a metal, a ring structure is formed which includes the metal as one of the ring members.

The organic layers can be manufactured using vacuum deposition, spin coating, organic vapor phase deposition, ink jet printing and other methods known in the art.

The organic photosensitive optoelectronic devices can function as a PV, photodetector or photoconductor. Whenever the optoelectronic photosensitive organic devices of the present invention function as a PV device, the materials used in the photosensitive organic layers and their thicknesses can be selected, for example, to optimize the external quantum efficiency of the device. Whenever the optoelectronic photosensitive organic devices of the present invention function as photodetectors or photoconductors, the materials used in the photoconductive organic layers and their thicknesses can be selected, for example, to maximize the sensitivity of the device to desired spectral regions.

This result can be achieved by considering several patterns that can be used in the selection of layer thicknesses. Is It is desirable that the diffusion length of the excitons, LD, be greater or comparable with the thicknesses of the layers, L, since it is believed that the greater dissociation of excitons will occur in an interconnection. If LD is less than L, then many excitons can recombine before dissociation. It is also desirable that the total thickness of the photosensitive layer be of the order of the absorption length of the electromagnetic radiation, 1 / (where a are the absorption coefficients), so that almost all of the radiation incident on the PV device It is absorbed to produce excitons. In addition, the thickness of the photoconductive layer should be as thin as possible to avoid excessive series resistance due to the high overall resistivity of the organic semiconductors.

Accordingly, these competing patterns implicitly require that intermediate points be created in the thickness selection of the photoconductive organic layers of a photosensitive optoelectronic cell. Therefore, on the other hand, a thickness that is comparable or greater than the absorption length is desirable (for a single-cell device) to absorb the maximum amount of incident radiation. On the other hand, as the thickness of the photoconductive layer increases, two undesirable effects increase. One is that because of the high series resistance of the organic semiconductors, the thickness of the organic layer increases the resistance of the device and reduces the efficiency. Another undesirable effect is that increasing the thickness of the photoconductive layer increases the possibility of generating excitons away from the effective field in a charge separation interconnection, which results in a higher probability of recombined recombination and again in reduced efficiency. Accordingly, a configuration of the device that balances between these competing effects in a form that produces a high external quantum efficiency for the total device is desirable.

The organic photosensitive optoelectronic devices of the present invention can function as photodetectors. In this embodiment, the device can be a multi-layer organic device, for example that described in US Patent Application No. 10 / 723,953, filed on November 26, 2003, incorporated herein by reference in its entirety. In this case an external electrical layer can be applied generally to facilitate the removal of the separated charges.

A concentrator or trap configuration can be used to increase the efficiency of the organic photosensitive optoelectronic device, where photons are forced to make several steps through 'the thin absorbent regions. U.S. Patent Nos. 6,333,458 and 6,440,769, incorporated herein by reference in its entirety, addresses this problem by using structural designs that increase the photoconversion efficiency of photosensitive optoelectronic devices by optimizing the optical geometry for high absorption and for with optical concentrators that increase the collection efficiency. These geometries for the photosensitive devices substantially increase the optical path through the material by trapping the incident radiation within a reflecting cavity or the waveguide structure, and thus recycling the light by multiple reflection through the photosensitive material. The geometries disclosed in U.S. Patent Nos. 6,333,458 and 6,440,769 accordingly increase the external quantum efficiency of the devices without producing a substantial increase in overall strength. Included in the geometry of these devices is a first reflective layer, a transparent insulating layer that must be longer than the optical coherence length of the incident light in all dimensions to prevent the effects of the interference of the optical microcavities; a first transparent electrode layer adjacent to the transparent insulating layer, a photosensitive heterostructure adjacent to the transparent electrode; and a second electrode that is also a reflector.

Coatings may be used to focus the optical energy on desired regions of a device. U.S. Patent Application No. 10 / 857,747, which is incorporated herein by reference in its entirety, provides examples of that coating.

The energy conversion efficiency (??) of the organic cells can be improved by using new materials and the introduction of novel device structures. The efficiency of the organic cells can be improved by using the C50 acceptor material with a long exciton diffusion length (LD «400 A), or forming a global heterojunction structure, where an interpenetration network of donor and acceptor materials increases the likelihood that the excitons will diffuse to a neighbor, "local" DA interconnection. One embodiment of the present invention provides an organic copper phthalocyanine (CuPc) / Ceo cell that incorporates a hybrid planar-mixed heterojunction (P-HJ), comprising a D-A layer sandwiched between homogeneous donor and acceptor layers. The device shows that ?? = 5% under stimulated AM1.5G solar illumination.

Stacking two or more cells in series is one way to harvest more photons while increasing the open circuit voltage (Voc) of the cell. A greater duplication of the efficiencies of the individual CuPc / PTCBI cells has been demonstrated. = 2.5%, as described in A. Yakimov and S.R. Forrest, Appl. Phys. Lett. 80, 1667 (2002), stacking two thin slices in series, with nanogroups of Ag between the subcells that provide sites for improvement of the optical field and efficient recombination for the photogenerated charges. The photoelectric voltage of this "tandem" cell can be double of each individual cell (or subcell). An embodiment of the present invention comprises two CuPc / C6o hybrid PM-HJ cells in series, where each cell has a different ratio of CuPc to C60. This configuration derives in ?? = (5.7 ± 0.3)% under 1 sol = 100 mW / cm2 of simulated AM1.5G solar illumination, which represents a 15% increase with respect to the hybrid PM-HJ cell. In addition, Voc of the tandem cell is larger than that of a PV cell, which reaches up to 1.2 V under high intensity illumination. One embodiment of the present invention employs the combination of the material of highly efficient CuPc and C60 materials in double planar-mixed heterojunction structures. Excluding antireflection coatings on substrates, organic PV cells with energy conversion efficiencies 6.5% solar energy may be possible using tandem structures of this type.

A CuPc / PTCBI tandem cell of two subcells has a symmetric spectral response of each of the two subcells. The optical interference between the incident light and that reflected from the metal cathode results in a maximum optical intensity at a perpendicular optical path length of X4 from the cathode / organic interconnection, where? is the wavelength of the incident light. As used herein, "perpendicular optical path length" refers to the distance / n, as measured normal to the surface of the device and integrated over the path that the light travels, where n is the refractive index of the material and may vary within of the material. Therefore, an "asymmetric" tandem cell with a frontal cell rich in molecules that absorb long wavelengths, and a posterior cell rich in molecules that absorb short wavelengths, can absorb more incident light than an equivalent tandem cell which has equal mixtures of CuPc and C6o in the subcell. For example, if CuPc absorbs between? = 550 nm and 750 nm, and CQO between? = 350 and 550 nm, a hybrid P-HJ cell of asymmetric CuPc / C60 may include a frontal cell with a thicker homogenous CuPc layer and a C60 layer thinner than the cell later. An intermediate point between the thicknesses of the homogeneous and mixed layers can also be used to balance the photoelectric current in the two subcells, due to the short diffusion lengths of the exciton in the homogeneous layers and the low change mobilities in the mixed layers.

The efficiency of a tandem P-HJ hybrid cell of CuPc / C6o can be maximized by modeling the characteristics of the current density as a function of the voltage (JV) of the subcell i (i = 1.2 indicating the frontal cells and subsequent, respectively) following: where Jd, i and Jph, are the densities of darkness and photoelectric current, respectively, JS (i is the inverted polarization saturation current, n ± is the ideality factor, Rs, i is the series resistance of the cell, is the charge of electrons, k is the Boltzmann constant and T is the temperature.Using a model that considers both the optical interference and the exciton diffusion, we can obtain the photoelectric current density J ° Ph, i under a density of incident optical energy P0, assuming that all photogenerated charges are collect on the electrodes. This assumption may not be maintained for the cell with a mixed layer, where the mobilities of the charge carriers are significantly reduced from those of the homogeneous layers due to molecular intermixing, which results in the recomposition of photogenerated charges within the mixed layer. The efficiency of load collection the proportion of the charges collected in the electrodes, as a function of the applied voltage V and the thickness of the mixed layer dm is where Lc (V) = Lc0 (Vbi-V) / V is the charge collection length, Lco is a constant, and Vbi is the built-in potential. Given JÍ = JÍ (Í) (i = 1,2), the JV characteristics of the tandem cell are obtained from the requirement that J = Jx = J2, V = Vi + V2, from which the performance parameters of the PV cell (short circuit current density JScr open circuit voltage Voc, load factor FF, and energy conversion efficiency ??).

Table 1 provides the structures of the three tandem cell devices. Table 2 summarizes the values of the parameters used in the model. Referring to the Table 1, the cell? it has thicknesses of the mixed layers based on the thicknesses of given asymmetric homogeneous layers, which derives at = 5.2% under 1 solar illumination sun of AM1,5G. The combination of the thicknesses of the photoactive layers of the B cell results in a higher efficiency of ?? = 5.9%. A PTCBI layer of the frontal cell can also contribute to the photoelectric current when the homogenous C6o layer of the frontal cell is removed, such that the CuPc molecules of the mixed layer can form a dissociation interconnect of excitons with PTCBI . This results in a higher Jsc and a ?? = 6.5% in the C cell, while the absorption of PTCBI fills the space between the absorption regions of CuPc and C6o, a? = 550 nm.

TABLE Front Cell Rear Cell Voc FF Cell Rupture CuPc Cso PTCBI CuPc CuPc: C6í Cso PTCBI (mA / ern4) (V) (¾! to c TABLE 2 3s P-3 n ¾ (A) rnA / cm *) (A) (V) C uP c C s or P TC BI 35 0, 25 1, 6 400 0, 65 80 400 30 In one embodiment of the invention, photoactive regions are arranged between two electrodes. In preferred embodiments of the invention, the photoactive regions comprise hybrid planar-mixed heterojunction (PM-HJ) devices, which are described in US Patent Application No. 10/822774, incorporated herein by reference in its entirety. Figure 2 shows an organic photoactive device 200 according to an embodiment of the invention. The device 200 may comprise a substrate 210 on which is deposited a first electrode 220, a first organic (or "front") photoactive region 230, an intervention layer 240, a second photoactive (or "back") region 250 and a second electrode 260. The organic photoactive regions 230 and 250 comprise an organic acceptor material and an organic donor material. In preferred embodiments of the invention, the first photoactive region 230 further comprises a first organic layer 231 comprising a non-mixed organic acceptor material; a second organic layer 232 comprising a mixture of the material of organic acceptor of the unmixed organic layer 231 and an organic donor material; a third organic layer 233, comprising the non-mixed donor material of the second organic layer 232; and an exciton blocking layer 234. In other preferred embodiments, the acceptor layers 231 and 251 or donor layers 233 and 253 may be absent. In another embodiment of the invention, the second photoactive region 250 comprises a similar arrangement of organic materials as the first photoactive region 230. In a preferred embodiment of the invention, the intervention layer 240 may comprise one or more electrodes, where several electrodes may be separated by an insulating layer.

In another embodiment of the present invention, the mixture of the organic acceptor material and the organic donor material in a mixed organic layer, such as the organic layer 232 can occur in a ratio in the range of 10: 1 to 11:10 in weight, respectively. In one embodiment, an organic layer including a mixture of acceptor and donor materials (such as organic layer 232) and an organic layer including an acceptor material or a donor material (such as the second organic layer) may be present. 231 or 233).

When an EBL is deposited in an adjacent layer and in direct contact with a deposited cathode, the EBL can be damaged. It is believed that this damage is advantageous in that it can allow load carriers to pass through the EBL more easily, while still preventing the excitons from doing so. It is believed that the selection of materials for EBL and organic acceptor layers such as the LUMO of each EBL is not more than 0.3 eV higher than the LUMO of the adjacent acceptor material produces a similar result. In order to obtain favorable charge transport properties, it is therefore preferable that an EBL arranged adjacent to an acceptor layer (1) is not separated from the second electrode by a photoactive region; and / or (2) have a LUMO no greater than 0.3 eV more than the LUMO of an adjacent photoactive region. If a particular EBL is not separated from the second electrode by a photoactive region, such that the EBL is subject to damage during the deposition of the second electrode, the difference in LUMO between the EBL and the acceptor is less important and the criteria used for selecting the EBL material can be more compensated for factors other than LUMO.

In a preferred embodiment of the device, the second exciton blocking layer 254 comprises a material different from the first exciton blocking layer 234. As the exciton blocking layer 254 is not separated from the second electrode by a photoactive region, a wider selection of materials may be available. The material of the exciton blocking material 254 may have a LUMO of not more than 0.3 eV greater than the LUMO of the organic acceptor layer 253, or it may have a LUMO that is larger, but the transport layer may still be favorable due to damage caused by the deposition of the second electrode 260. Preferred materials for the exciton blocking layer 254 include BCP and preferred materials for the exciton blocking layer 234 include PTCBI.

In another embodiment of the invention, the organic cell 200 further comprises an intervention layer 240. The intervention layer 240 may comprise a charge recombination zone. In a preferred embodiment of the invention, the charge recombination zone comprises an organic material interrupted with p, such as m-MTDATA: F4-TCNQ or BTQBT: PTCDA, and the charge recombination zone further comprises nanoparticles 241. It is especially preferable that the nanoparticles comprise Ag or another metal or metallic material. Other materials can be used.

In a tandem cell, it may be advantageous to use different acceptor and donor materials, or the same acceptor and donor materials in different ratios, in each subcell. He Use of different materials or different ratios of the same materials may allow the cell to absorb light in a greater range of wavelengths than if the same materials are used in the same ratios in each -sub-cell. In a preferred embodiment of the invention, the organic regions 230 and 250 comprise different acceptor and donor materials. The organic regions 230 and 250 may also comprise the same acceptor and donor materials, wherein the mixed organic layers 232 and 252 comprise different ratios of the acceptor and donor materials. The organic acceptor material of the organic regions 230 and 250 can be C6o. The organic donor material of the photoactive regions 230 and 250 can be CuPc. Other organic donor materials include lead phthalocyanine (PbPc), metal-containing porphyrins, non-metal porphyrins, metal-containing phthalocyanines, metal-free phthalocyanines, diamines (such as NPD), and variants with functionalities thereof, including naphthalocyanines. Other suitable organic acceptor materials include PTCBI, C7o, fullerenes, perylenes, catacondelated conjugated molecular systems such as linear polyacenes (including anthracene, naphthalene, tetracene, and pentacene), pyrene, coronen, and variants with functionalities thereof. This list is not limited, and other acceptor and donor materials may also be used.

In an especially preferred embodiment of the present invention, the anode comprises a layer of conductive indium tin oxide (ITO), transparent on a glass substrate, and the cathode comprises a thermally evaporated Ag electrode of 1000 A. The photoactive region of each subcell comprises a hybrid PM-HJ, that is to say a layer of mixed CuPc: C6o arranged between homogeneous CuPc and C6o layers, which combines the advantages of a planar HJ between homogeneous layers (good transport of photogenerated charge carriers to their respective electrodes) and a mixed layer (high exciton diffusion efficiency). A thin layer of 3,4,9, 10-perylentetracarboxylic bis-benzimidazole (PTCBI) and batocuproin (BCP) is used as the exciton blocking layer (EBL) in the frontal (closer to ITO) and posterior subcells (more near the cathode), respectively, thus forming a high efficiency double heterojunction PV structure. A charge recombination zone for the electrons generated in the frontal cell and gaps generated in the posterior cell is arranged between the subcells. The recombination centers comprise Ag nanogroups deposited in an ultra-thin layer (5 A, average thickness) disposed in a 4,4 ', "-tris (3-methyl-phenyl-phenyl-amino) triphenylamine (m-MTDATA) of 50 A thickness interrupted with p with 5 mol% of tetrafluoro-tetracyano-quinodimethane (F4-TCNQ).

Manufacturing methods and device characterization methods may be those known in the art.

It is understood that the embodiments described herein are examples only, and that other embodiments may be used in accordance with the present invention. For example, the order of the illustrated layers can be altered. For example, the positions of the organic layers 230 and 250 can be switched, with proper repositioning of the blocking layers, etc. Additional layers may be present, such as blocking layers, charge recombination layers, etc. For example, the blocking layers may be removed, and / or additional blocking layers may be present. Non-organic regions may be present and may be used to adjust the position of the organic regions relative to a reflective layer. Materials other than those specifically described may be used. For example, a device where all of the electrodes are ITO can be manufactured in such a way that the device can be transparent to some extent. In addition, the device can be fabricated on a substrate, and then applied to a support surface, such that the last deposited electrode is closer to the support surface. The acceptor and donor layers may not be present. For example, the donor or acceptor layers 231, 251, 233 and 253 may be absent.

Although many embodiments are described with respect to solar cells, other embodiments may be used in other types of devices, such as a photodetector.

When a layer is described as an "unmixed" acceptor or donor layer, the "unmixed" layer can include very small amounts of the opposite material as an impurity. A material can be considered an impurity if the concentration is significantly lower than the amount necessary for the infiltration in the layer, ie less than 5% by weight. Preferably, any impurity is present in a much smaller amount, for example less than 1% by weight or more preferably less than 0.1% by weight. Depending on the processes and parameters of the processes used to fabricate devices, some impurities from immediately adjacent layer materials may be unavoidable.

Organic materials can have absorption spectra with maximum values at specific wavelengths. As used herein, the term "characteristic absorption wavelength" refers to the wavelength at which the absorption spectrum of a material has a maximum.

The device 200 may include at least one reflective layer. In an embodiment of the invention, the second electrode 260 is a reflective layer. Other configurations may be used, such as the use of a separate reflective layer, or a superior emitting (or absorbing) device where the substrate or the first electrode is the reflective layer. A "reflective" layer may be a metal layer, or other type of reflecting layer, such as an aperiodic or periodic dielectric cell. The use of a reflective layer results in an optical field resistance that varies with the wavelength and with the position in a direction perpendicular to the reflective layer. For any given wavelength, there are maxima in the resistance of the optical field as a function of position. See, for example, Figure 3. For photosensitive devices, it is desirable to place a photoactive region having a particular characteristic absorption wavelength such that the position having a maximum as a function of the position for that wavelength It is located in or near the photoactive region. For a photoactive region having several materials, the characteristic absorption wavelength is based on the maximums of the absorption spectra of the entire region. "Near" can mean, for example, at a distance that is not greater than 0.5? /? of the photoactive region in question, where n is the refractive index of the material in which the maximum occurs. Preferably, the maximum is disposed within the photoactive region. The location of the photoactive region in this way results in improved absorption. For some applications, it is desirable to use the region of light absorption that has significantly different absorption wavelengths. That difference can allow the absorption of a wider range of wavelengths. In one embodiment of the invention, the organic regions 230 and 250 have absorption wavelengths characteristic to? and? 2, respectively. It is preferred that? A is 10% different from% 2- The characteristic wavelength of absorption is only one way to quantify "different" absorption spectra. Another way to quantify different absorption spectra is that the wavelength of at least one of the three upper absorption peaks of a photoactive region is at least 10% different from all of the wavelengths of the first 3 peaks of absorption of another photoactive region. Yet another way to quantify different absorption spectra is to superimpose two normalized spectra on top of each other, and measure the area that overlaps. If this area of overlap is 80% or less of the total area of one of the spectra, the spectra can be considered significantly different. For example, two materials may have lengths absorption wave characteristics similar, but other characteristics (such as subpics) that are significantly different and possibly complementary in order to absorb a broad spectrum of incident light. It is desired that that embodiment be within the scope of certain aspects of the invention.

Many photoactive materials (and combinations of materials, for photoactive regions having various materials) can have a number of absorption peaks. A photoactive region that strongly absorbs a particular wavelength of light can be placed in a position where the resistance of the optical field for that wavelength is strong. In one embodiment, a local peak is used in the absorption spectra of a photoactive region to determine a favorable position for the photoactive region. The photoactive region may be located at or near the optical field strength for the wavelength for which the photoactive region has a local maximum. For devices that are desired to absorb the solar spectrum, wavelengths between 350 and 1300 nm may be more important. Generally speaking, it is preferable to increase or maximize the superposition of the optical field strength to a particular wavelength or wavelength range with a photoactive region that is a strong absorber of those wavelengths. One way to achieve this is adjusting the position of a photoactive region to a position where there is a greater overlap between the absorption of the photoactive region and the intensity of the optical field (both as a function of wavelength). Another way is to alter the absorption characteristics of a photoactive region by altering the materials of it, or the ratio of the materials, to achieve a greater overlap between the absorption spectrum and the intensity of the optical field (both depending on the length of wave) in the position of the photoactive region.

One way to describe that equality is to determine the wavelength of the first 3 absorption peaks for a photoactive region, and to place the photoactive region so that a peak in the optical field strength for one of these three wavelengths is in the photoactive region or within 0.05? /? of the photoactive region, where? it is the wavelength of the peak that equals the maximum in the resistance of the optical field, and n is the refractive index of the layer in which the peak is located in the intensity of the optical field. Another way to describe that equality is to consider the wavelengths of all the absorption peaks of the photoactive region (s). The "wavelength" of an absorption peak is the local maximum of the absorption spectra for the peak, and the "first three" peaks are the peaks that have the three highest local maximums. When determining the "first" wavelength or wavelengths, the range of wavelengths may be limited in some embodiments. For example, for some devices designed to absorb the solar spectrum, the range of wavelengths considered can be limited to 350 - 1300 nm because a significant fraction of the usable energy of the solar spectra is within this range, although they can also be used wider ranges in some embodiments, including embodiments intended to absorb the solar spectrum.

Locating photoactive regions as described can result in an increase in the amount of incident light absorbed. In preferred embodiments of the invention, materials and positions of the photoactive regions are selected such that at least 10% and more preferably at least 20% of the total incident electric field intensity is located in a photoactive region having absorption characteristics in such a way that energy can be absorbed. As used herein, "optical field strength" refers to the integral of the square of the electric field over a region. Therefore, the intensity of the total incident electric field is the integral of the square of the optical field over the entire device, and the total electric field of the photoactive regions is the sum of the Integrated electric field over each of the photoactive regions. Therefore, for the R region, the IR intensity is as will be appreciated by an expert in the art. In addition, the intensity of the optical field at each point is also a function of the wavelength. It is preferred to increase the integral as a function of the position on the photoactive regions of the device: the integral over the wavelength of the product of the absorption characteristic of the photoactive region (which may be a function of the position and the wavelength ) with the intensity of the optical field (which can also be a function of position and wavelength). This amount, divided by the intensity of the total optical field, is the percentage of the intensity of the optical field that can be absorbed by the device, and which is preferably at least 10% and more preferably at least 20%. The percentage of the intensity of the optical field that it can absorb can be increased, for example, by selecting materials that are good absorbers of particular wavelengths of light, and placing them where the intensity of the optical field for that particular wavelength is important. It is believed that this results in greater absorption by the photoactive regions, and therefore in an improved efficiency of the device. In a preferred embodiment, the intensity of the optical field is based on a solar spectrum. Note that peak equality may not be the only way to achieve the 10% 20% described above. Matching photoactive regions that have strong absorption at a particular wavelength (regardless of whether there is a peak) with a strong value for the wavelength in the optical field strength is one way to achieve this goal. By calculating the integral described above, it is possible to determine whether a device will have strong absorption or not.

For the case of a single reflective layer, which is a good approximation of many embodiments, there is a maximum in the resistance of the optical field for a particular wavelength X at an optical path length? / 4 distant from the reflective layer. Therefore, it is also preferred that at least a portion of the first photoactive region 250 be disposed at a perpendicular optical path length of / 4 + 25% from the edge of the reflector layer closest to the photoactive region, and at least a part of the second photoactive region 230 is disposed at a perpendicular optical path length 2 2/4 ± 25% from the edge of the reflector layer closest to the second photoactive region, where ?? and? 2 are the wavelengths at which the first and second photoactive regions are strong absorbers. A "strong absorbent" can be quantified in numerous ways. In one embodiment, the wavelength of at least one of the absorption peaks of the second photoactive region may be greater than the wavelength of at least one of the absorption peaks of the first photoactive region. In another embodiment, the wavelength of at least one of the first three absorption peaks of the second photoactive region may be greater than the wavelength of at least one of the first three absorption peaks of the first photoactive region. The 25% margin is a measure of how far the wavelength of the absorption peak can be from the maximum in the optical field resistance, while still maintaining a significant overlap between strong optical field strength and strong absorption for that wavelength and near wavelengths. More generally, in the case of a single reflective layer and configurations having a similar optical field strength profile, it is preferred to place materials that absorb longer wavelengths proportionally farther from the reflecting surface than materials that absorb wavelengths. shorter wave, where the constant of proportionality is? / ?, where n is the refractive index of the materials in the stack. When n varies across the stack, an index of medium refraction spatially compensated for the materials comprising the stack. For more complex optical configurations, one skilled in the art, with the benefit of this invention, will be able to determine the location of the maximums in the optical field resistance.

In an embodiment of the invention, there is provided a photoactive device having several photoactive regions with different absorption characteristics, disposed between a first electrode and a second electrode. Preferably, the absorption characteristics are selected to complement one another, such that a photoactive region absorbs preferentially in a first range of wavelengths, and the second photoactive region absorbs preferentially in a second range of wavelengths. different wave of the first range. A range of wavelengths centered around a wavelength ?? Can it be considered significantly different from another range? 2 yes? and? 2 are at least 10% different. By "preferentially" it is meant that a photoactive region is a stronger absorber than another photoactive region with which it is being compared. A photoactive region that "preferentially" absorbs a particular range of wavelengths does not need to be a particularly strong absorber of those wavelengths, or have a maximum in the absorption spectra at those wavelengths, although these criteria would be preferable. The "preferential" absorption in a particular range of wavelengths means that a photoactive material is a better absorber than another photoactive material with which it is being compared.

In order to compare how well two different photoactive regions absorb in a particular range of wavelengths, the "average absorption" in the range in question is a useful amount. The absorption - average is the integral over the range of wavelengths of the absorption spectra, divided by the wave width range. For a photoactive region that has different concentrations of materials in different places, the average absorption is the integral over the wavelength and the position of the absorption spectra, which can be a function of wavelength and position, divided by the width of the range of wavelengths and the volume of the material. The average absorption allows a comparison that takes into account peaks and valleys located within the range, without providing undue weight to absorption at any wavelength. The average absorption over the range of? ± 5% provides a useful milestone for designing devices.

Can two photoactive regions be considered to have significantly different absorption characteristics in a range centered at one wavelength? Particular if the average absorption for a range? + 5% for the two regions since it is at least 5% different. Similar differences in average absorption can be the result of involuntary variations in manufacturing processes, or other factors that do not significantly point to controlling the absorption spectra.

The amount of energy that a particular photoactive region can absorb in a particular wavelength range is determined by the absorption characteristics of the photoactive region and the intensity of the optical field for the wavelength range. Mathematically, the integral over the space of the photoactive region and over the range of wavelengths of the optical field strength by the absorption characteristic (both as a function of the position and the wavelength) provides a measure of this energy . Multiplying the average absorption and intensity of the average optical field in the wavelength range and the position is a way of quantifying this concept. The "average optical field strength" of a photoactive region is the integral over space and length Wavelength of the optical field strength, divided by the volume of the space and the width of the wavelength range.

To optimize the amount of energy absorbed by a photoactive region, it is desirable to superpose a high absorption characteristic over a range of wavelengths with a high intensity of the optical field over the same wavelength range. However, there are many other factors that affect the design of the device. Due to manufacturing considerations, it may be desirable to limit the amount of materials used to make the device. The properties of materials other than absorption, for example conductivity and injection of the charge carrier into other materials, can also fulfill a function. The position of the photoactive regions can be affected by factors other than the intensity of the optical field, for example a desire for blocking layers, injection layers, electrodes, recombination regions, etc. of different thicknesses In some embodiments of the invention, the absorption of light by a tandem solar cell is optimized by selecting the absorption characteristics and the positions of the photoactive regions, possibly subject to other different limitations. A tandem solar cell has at least two regions Stacked photoactive and can have more than two. A tandem cell can be considered "optimized" if it includes at least two photoactive regions with different absorption characteristics, and the cell absorbs significantly more light than an otherwise equivalent device where -the photoactive regions have the same absorption characteristic, ie absorption characteristics that are not significantly different. The optimization can be extended to more than 2 cells.

In an embodiment that includes more than 2 cells, some of the cells may have photoactive regions with the same absorption characteristic. The resistance of the optical field for a particular configuration of the device may have more than one region where the resistance of the optical field for a particular range of wavelengths is high. It may be desirable to place several cells that have the same absorption characteristic (ie, absorption characteristics that are not significantly different), which preferentially absorb a particular range of wavelengths, in several places in a device where the resistance of the Optical field for that range of wavelengths is high. For example, in devices having a reflective layer, the resistance of the optical field for a particular wavelength may have local maxima at periodic distances from the reflective layer, starting at a distance of? / 4 and recurring every? / 2 after it, that is, there may be local maxima to? / 4, 3? / 4, 5? / 4, etc. Therefore, it may be desirable to place cells that preferentially absorb a wavelength? at distances / 4 and / 5 of the reflecting layer, with a cell that preferentially absorbs a different wavelength z disposed between the two cells that absorb at. preferential form ?? ', preferably in a location where the optical field resistance for the wavelength ?? is high.

While many embodiments of the invention are described with respect to two stacked cells, it is understood that a greater number of stacked cells can be used, and concepts related to the position of the cells and the blocking layers used adjacent to the cells are Generally applicable to batteries that have more than two cells.

As used herein, and as would be understood by one skilled in the art, the term "blocking layer" means that the layer provides a barrier that significantly inhibits the transport of charge carriers and / or excitons through the devices, without suggesting that the layer necessarily completely blocks the charge carriers and / or excitons. The presence of that layer of Blocking in a device can result in substantially higher efficiencies compared to a similar device that does not have the blocking layer.

Figure 3 shows the intensities of the optical field a? = 450 nm (full line) and a? = 650 nm (dotted line) as a function of the distance from the cathode in the tandem organic B cell (see Table 1), where the structure is shown schematically in the upper part of Figure 3. The intensity a? = 450 nm has peaks at 400 A from the reflector Ag cathode, or 300 A closer than it stops? = 650 nm. Therefore, making the frontal cell rich in materials that absorb shorter wavelengths and that the posterior cell is rich in materials that absorb lower wavelengths can result in greater absorption of a broad spectrum. In cell B the posterior cell has a homogeneous C60 layer substantially thicker than the frontal cell, which results in a higher external quantum efficiency in the absorption region of C6o (? <550 nm), as shown in Figure 4. As the intensity of light a? «650 nm is located mainly in the frontal cell, quantum efficiency at 500 nm < ? < 750 nm may be higher for the frontal cell, although the thicknesses of the homogeneous CuPc and the mixed layers are approximately the same in both subcells to balance their photoelectric currents.

Figure 4 shows the external quantum efficiency spectra calculated for the frontal cell (dotted line) and posterior (full line) of the B cell. The asymmetric spectral responses from the two subcells derive from 1. asymmetric tandem cell structure as well as optical interference.

Figure 5 shows the current density characteristics as a function of the voltage (J-V) of the asymmetric tandem A cell, in the dark and under different intensities of simulated AM1.5G solar illumination. The experimental J-V characteristics of tandem cell A in the dark and under different intensities of simulated AM1.5G solar illumination are shown (open symbols). A rectification ratio of 105-106 to ± 1.5 V is typical. The open circuit voltage is V0c = 1.04 V under an illumination of 1 sun, and approaches 1.2 V under 10 suns, which can be twice that of a cell of a hybrid PM-HJ of CuPc / C6o- Full lines are JV modeled features, which matches the experimental data except for the dark polarization current inverted, in which case the generation-recombination current or thermally assisted tunneling can contribute significantly to J¿.

Figure 6 shows the dependence of the measured illumination intensity (P0) with respect to the energy conversion efficiencies (??) of different organic tandem cells (A, filled squares, B, open circles, C, full triangles) under a simulated AM1.5G solar illumination, compared to those of 5% of a single planar-mixed hybrid CuPc / Ceo heterojunction cell (open inverted triangles). The energy conversion efficiency of tandem cell A (full squares), derived from the experimental J-V characteristics of Figure 5, reaches a maximum of ?? = (5.4 + 0.3)% at Po = 0.34 soles. Under a higher intensity illumination, the FF decreases (see Figure 7) due to the relatively thick mixed layers. With thinner mixed layers, the tandem B cell (open circles) has a high FF = 0.56 even under intense illumination of 11 suns. This drift in ?? = (5, 7 ± 0, 3)% at P0 > 1 sun, according to the model. However, the tandem C cell (full triangles) has a lower efficiency than the model prediction (6.5%), mainly due to a low FF = 0.51.

This may suggest a small energy barrier in the interconnection of C60 / PTCBI that prevents the transport of electrons to the cargo recombination zone. However, the efficiencies of tandem A and B cells are higher than the cell of a 5% CuPc / C6o hybrid PM-HJ (open inverted triangles in Figure 6), which demonstrates the efficiency of stacking cells .

Figure 7 shows the load factor (FF) of the tandem cells and a single hybrid PM-HJ shown in Figure 6. Under a higher intensity illumination, the FF decreases due to the relatively thick mixed layers . With thinner mixed layers, the tandem B cell (open circles) has a high FF = 0.56 even under an intense illumination of 11 suns.

Figure 8 shows two possible geometries of a PV 810 and 820 device, with representative perpendicular optical path lengths 815 and 825. The perpendicular optical path length is measured normal to the surface of the device.

Figure 9 shows absorption spectra of CuPc / Cgo films with different mixing ratios, deposited on ITO. The concentrations of CuPc in mixed films are 100% of CuPc (a single layer of CuPc) 910, 62% of 920, 40% of 930, 33% of 940 and 21% of 950. The pure CuPc film has two peaks centered at wavelengths of 620 nm and 695 nm . The peak of the longest wavelength is due to the generation of Frenkel excitons, while the shorter wavelength characteristic is attributed to the formation of CuPc aggregates. The longest wavelength peak is dominant in the gas phase or the diluted solution. Figure 9 shows that the magnitude of the longest wavelength peak increases with the increase of the C6o- content. Therefore, the CuPc molecules show a lower tendency to aggregate with the increase of the C6o content. This suggests that an increase in C6o concentration inhibits the aggregation of CuPc, thus reducing the transport of voids in the mixed film, perhaps resulting in low carrier collection efficiency. This is reflected in the reduced energy efficiency (?? = (2.6 ± 0.1)%, see Table 2) of a PV cell of the mixed layer of CuPc: C60 (1: 2). However, at a concentration of 1: 1, there is a sufficient aggregation of CuPc molecules to allow low transport of low resistance holes, while C60 molecules of much higher symmetry can also form an infiltration path for the efficient electron transport to the cathode.

Table 1 shows the thicknesses of the layers (in A) of three organic tandem photovoltaic cells as well as predicted performance parameters (short circuit current density JSCÍ open circuit voltage Voc, fill factor FF and conversion efficiency of eneregia? ?) under 1 sun of solar illumination of AM1,5G. The charge recombination zone in each tandem cell consists of an Ag nanogroup layer of 5 A thickness and an m-MTDATA 50 A thickness interrupted with 5 mol% F4-TCNQ.

Table 2 shows the parameters used in the modeling of the J-V characteristics of the PV cells in tandem hybrid PM-HJ CuPc / C6o- It is understood that the embodiments described herein are exemplary only and that other embodiments may be used in accordance with the present invention. For example, the order of the layers illustrated can be altered. For example, in Figures 1 and 2, the positions of the photoactive layers, ie the organic regions 230 and 250 can be switched, with an appropriate repositioning of the blocking layers, etc. Additional layers may also be present or not, such as blocking layers, layers of charge recombination, etc. For example, blocking layers and / or additional blocking layers can be removed. Non-photoactive regions may be present and may be used to adjust the position of the photoactive regions relative to a reflective layer. Different configurations of solar cells can be used, for example solar cells in tandem. Materials other than those specifically described may be used. For example, a device where all the electrodes are ITO can be manufactured in such a way that the device can be transparent to some extent. In addition, the device can be fabricated on a substrate, and then applied to a support surface, such that the last deposited electrode is closer to the support surface. Although many embodiments are described with respect to solar cells, other embodiments may be used in other types of photoactive devices having a D-A heterojunction, such as a photodetector.

The energy efficiencies achieved by the embodiments of the invention are higher than the previous efficiencies achieved for organic solar cells. These results may be due to interactions between several characteristics of the embodiment of the invention, including the use of an unmixed organic photoactive layer in relation to an organic photoactive layer mixed, with thicknesses and selected positions taking into account the efficiency. Embodiments of the invention may be able to achieve energy conversion efficiencies that approach those of a-Si cells, currently in production, with efficiencies of 7 &-10%. It is expected that with the refinement of the devices according to the embodiments of the invention, even higher energy efficiencies can be achieved. For example, by applying simple anti-reflection coatings to glass substrates, an improvement of an additional 10% of the efficiencies may be possible, which suggests that the tandem cell structure proposed here can achieve efficiencies greater than 7%. Stacking more than two cells in series can help harvest more light, although it is more difficult to obtain an efficient cell structure. A final advantage of the asymmetric tandem cell structure is that it allows the incorporation of combinations of different donor and acceptor materials into the individual sub-cells to cover a wider region of the solar spectrum than the current CuPc-C6o system. Provided high production yields and long operating durations are possible in properly packaged solar cell modules, the asymmetric hybrid PM-HJ tandem cell has considerable potential for use in a variety of applications.

EXAMPLES In one embodiment of the invention, an efficient photovoltaic cell is provided, a cell with two stacked hybrid mixed planar heterojunction cells was fabricated on a glass substrate previously coated with transparent conductive ITO. The device has the structure: ITO / 75 A CuPc / 122 A CuPc: C6o (1.2: 1 by weight) / 80 A Cso / 50 A PTCBI / 5 A Ag / 50 A m-MTDATA: F4-TCNQ / 50 A CuPc / 132 A CuPc: C60 (1.2: 1 by weight) / 160 A C60 / 75 A BCP / Ag. The cell farthest from the cathode is slightly rich in CuPc, which absorbs in the spectral region of 550 nm to 750 nm, while the cell closest to the cathode is rich in absorbing in the spectral region from 350 nm to 550 nm. A maximum energy efficiency was measured from (5,6 + 0,3)% under 1 to 4 suns of simulated AM1,5G solar illumination.

Organic hybrid blended planar heterojunction photovoltaic cells were fabricated on glass substrates precoated with a conductive ITO anode, transparent 1500 A with a sheet strength of 15 O / sq. The substrates were cleaned in solvent followed by treatment with ozone with ultraviolet radiation for 5 minutes. The organic layers and a metal cathode were deposited by thermal evaporation in a high vacuum chamber with a base pressure of 2 × 10 ~ 7 Torr.

A layer of CuPc with a thickness of dD 50 A - 200 A, a layer deposited together of CuPc (1: 1 by weight) with a thickness of dm 0 - 300 A and a layer of? Β? with a thickness of dA 250 A - 400 A, they are deposited in sequence on the ITO anode, followed by a blocking layer of 100 A excitons of BCP thickness. Finally, an Ag layer of 1000 thickness was evaporated through a shade mask with holes 1 mm in diameter.

The current and voltage characteristics of the PV cells at 25 ° C in the shade and under solar illumination of simulated AM1.5G from a 150 W Xe arc lamp (Oriel Instruments) were measured using an HP semiconductor parameter analyzer 4155B. The intensity of illumination was varied using neutral density filters was measured with a calibrated broadband optical energy meter (Oriel Instruments).

Although the present invention is described with respect to particular examples and preferred embodiments, it is understood that the present invention is not limited to these examples and embodiments. The present claimed invention may accordingly include variants of the particular examples and preferred embodiments described herein, as will be apparent to one skilled in the art.

Claims

1. A device comprising: a first electrode; a second electrode; a first organic photoactive region disposed between the first electrode and the second electrode; and a second organic photoactive region disposed between the first electrode and the second electrode; wherein the first organic photoactive region and the second organic photoactive region have different absorption characteristics; wherein the device includes a reflective layer, and the first organic photoactive region and the second organic photoactive region are disposed on the same side of the reflective layer.

2. The device according to claim 1, wherein the device absorbs at least 10% of the intensity of the optical field when the device is exposed to incident light having a solar spectrum.

3. The device according to claim 1, wherein the device absorbs at least 20% of the intensity of the total optical field when the device is exposed to incident light having a solar spectrum.

4. The device according to claim 1, wherein the first organic photoactive region is disposed closer to the reflective layer than the second photoactive region. organic, and where the wavelength of at least one of the first three absorption peaks of the first photoactive region.

5. The device according to claim 4, wherein the wavelength of at least one of the first three absorption peaks of the second photoactive region is at least 10% greater than at least one of the first three absorption peaks of the first photoactive region.

6. The device according to claim 1, wherein the first organic photoactive region is disposed closer to the reflective layer than the second organic photoactive region, and wherein the second organic photoactive region is a stronger absorber at wavelengths greater than The first organic photoactive region.

7. The device according to claim 1, wherein the first electrode is the reflective layer.

8. The device according to claim 1, wherein at least a part of the first organic photoactive region is disposed at a perpendicular optical path length of ?? / ± 25% from the edge of the reflector layer closest to the first region. photoactive organic and at least a part of the second organic photoactive region is arranged at a perpendicular optical path length of 2 2/4 + 25% from the edge of the reflector layer closest to the second organic photoactive region, where ?? is the wavelength of one of the first three absorption peaks of the first organic photoactive region, and? 2 is the wavelength of one of the first three absorption peaks of the second photoactive region.

9. The device according to claim 1, wherein each photoactive region further comprises: an organic acceptor material; and an organic donor material in direct contact with the organic acceptor material.

10. The device according to claim 9, wherein each organic photoactive region includes the same organic acceptor material and the organic donor material, and wherein the first organic photoactive region and the second organic photoactive region comprise a different ratio of the organic material. organic acceptor and organic donor material.

11. The device according to claim 10, wherein the organic donor material of each organic photoactive region is CuPc and the organic acceptor material of each organic photoactive region is Ceo.

12. The device according to claim 11, wherein the organic acceptor material and the organic donor material of the first organic photoactive region are different from the organic acceptor material and the organic donor material of the second organic photoactive region.

13. The device according to claim 12, wherein the organic donor material of the first organic photoactive region is CuPc, the organic acceptor material of the first organic photoactive region is Cso, the organic donor material of the second organic photoactive region is PbPc and the organic acceptor material of the second organic photoactive region is PTCBI.

14. - The device according to claim 1, wherein each photoactive region further comprises: a first organic layer comprising a mixture of an organic acceptor material and an organic donor material; a second organic layer in direct contact with the first organic layer, wherein the second organic layer comprises a non-mixed layer of the organic donor material of the first organic layer and a third organic layer in direct contact with the first organic layer, wherein the third organic layer comprises a non-mixed layer of the organic acceptor material of the first organic layer; wherein the exciton blocking layer is disposed adjacent and in direct physical contact with the third organic layer.

15. The device according to claim 1, wherein each photoactive region further comprises a first organic layer comprising a mixture of an organic acceptor material and an organic donor material; and a second organic layer in direct contact with the first organic layer, wherein the second organic layer comprises a non-organic layer. mixed organic donor material of the first organic layer; wherein the exciton blocking layer is deposited adjacent to and in direct physical contact with the first organic layer.

16. The device according to claim 1, wherein each photoactive region comprises: a first organic layer comprising a mixture of an organic acceptor material and an organic donor material; and a second organic layer in direct contact with the first organic layer, wherein the second organic layer comprises a non-mixed layer of the material. of organic acceptor of the first organic layer; wherein the exciton blocking layer is disposed adjacent to and in direct physical contact with the second organic layer.

17. The device according to claim 1, wherein each photoactive region further comprises: a first organic layer comprising a non-mixed layer of the acceptor and donor material; and a second organic layer in direct contact with the first organic layer comprising an unmixed layer of the organic donor material; wherein the exciton blocking layer is disposed adjacent and in direct physical contact with the first organic layer.

18. The device according to claim 1, wherein each photoactive region comprises: a first organic layer comprising a mixture of an organic acceptor material and an organic donor material, wherein the exciton blocking layer is disposed adjacent and in direct physical contact with the first organic layer.

19. The device according to claim 1, wherein the device is a photovoltaic device.

20. The device according to claim 1, wherein the device is a photodetector.

21. The device according to claim 1, wherein the device further comprises a third photoactive region.

22. A device comprising: a first electrode; a second electrode; a first organic photoactive region disposed between the first electrode and the second electrode; a second organic photoactive region disposed between the first electrode and the second electrode; wherein the device includes a reflective layer, and the first organic photoactive region and the second organic photoactive region are disposed on the same side of the reflective layer; where ?? is the wavelength of one of the first three absorption peaks of the first photoactive region, and? 2 is the wavelength of one of the first three absorption peaks of the second photoactive region; where ?? is at least 10% different from? 2; wherein the first organic photoactive region is arranged in a position such that it is a maximum in the optical field resistance for the wavelength? within the first organic photoactive region, or within 0.05 ?? /? ¾ of the first organic photoactive region, where na is the refractive index of the material in which the maximum occurs; and wherein the second organic photoactive region is disposed in a position such that there is a maximum in the optical field resistance for the wavelength λ 2 within the second organic photoactive region or within 0.05 2 2 / ¾. of the first organic photoactive region, where nb is the refractive index of the material in which the maximum occurs.

23. A device comprising: a first electrode; a second electrode; a first organic photoactive region disposed between the first electrode and the second electrode; and a second organic photoactive region disposed between the first electrode and the second electrode; wherein the first organic photoactive region and the second organic photoactive region have different absorption characteristics; wherein the average absorption of the first photoactive region is greater than the average absorption of the second photoactive region in a range of wavelengths ?? ± 5%; wherein the average absorption of the second photoactive region is greater than the average absorption of the first photoactive region in a range of wavelengths? 2 ± 5%; where? 2 is at least 10% greater than ??

24. The device according to claim 23, wherein the device includes a reflective layer, and wherein the first organic photoactive region and the second organic photoactive region are arranged on the same side of the reflecting layer and wherein the first photoactive region is disposed closer to the reflective layer than the second photoactive region.

25. The device according to claim 24, wherein the first electrode is the reflective layer.

26. The device according to claim 4, wherein the first electrode and the second electrode are not reflectors.

27. The device according to claim 23, wherein the average absorption of the first photoactive region is at least 5% greater than the average absorption of the second photoactive region in a range of wavelengths ?? ± 5%; and wherein the average absorption of the second photoactive region is at least 5% greater than the average absorption of the first average region over a range of wavelengths% 2 ± 5%.

28. The device according to claim 23, wherein the first photoactive region and the second photoacative region comprise the C60 and CuPc materials and the percentage of C6o in the first photoactive region is greater than the percentage of C6o in the second photoactive region.

29. The device according to claim 23, wherein the average optical field strength for the range of wavelengths ± 5% at the position of the first photoactive region is greater than the average optical field strength for the range of X ±± wavelengths 5% at the position of the second photoactive region and where the average optical field strength for the wavelength range? 2 ± 5% at the position of the second photoactive region is greater than the intensity of the average optical field for the range of wavelengths? 2 ± 5% at the position of the first photoactive region.

30. The device according to claim 27, wherein the intensity of the average optical field for the wavelength range? ± 5% at the position of the first photoactive region is greater than the average optical field strength for the wavelength range? ± 5% at the position of the second photoactive region, and where the average optical field strength for the wavelength range? 2 ± 5% at the position of the second photoactive region is greater than the average optical field strength for the range of wavelengths? 2 ± 5% at the position of the first photoactive region.

31. The device according to claim 23, further comprising a third organic photoactive region disposed between the first electrode and the second electrode.

32. The device according to claim 31, wherein the first organic photoactive region, the second organic photoactive and the third photoactive region each of which has different absorption characteristics; wherein the average absorption of the third photoactive region is greater than the average absorption of the first photoactive region and the average absorption of the second photoactive region over a range of wavelengths? 3 ± 5%; wherein the average absorption of the first photoactive region is greater than the average absorption of the third photoactive region in a range of wavelengths ?? ± 5%; and wherein the average absorption of the second photoactive region is greater than the average absorption of the third photoactive region in a range of wavelengths 22 ± 5%.

33. The device according to claim 31, wherein the third photoactive region has an absorption characteristic that is the same as the absorption characteristic of the first photoactive region.