HK1160701A - Organic photosensitive devices comprising a squaraine containing organoheterojunction and methods of making the same - Google Patents

Description

Organic photosensitive devices comprising squaraines containing organic heterojunctions and methods of making the same

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is based on and claims priority from U.S. provisional patent application No. 61/097,143 entitled "Organic Photosensitive Devices Containing Organic heterojunctions and Methods of Making the Same," filed on 15.9.2008, "Organic Photosensitive Devices Containing squaric acid and Methods of Making the Same," which is hereby incorporated by reference in its entirety.

Joint research protocol

The claimed invention is made by, in the name of, and/or in conjunction with, participants to the following university-corporation joint research agreement: southern California University (The University of Southern California), The board of Michigan University (The Regents of The University of Michigan), and Global light Energy Corporation (Global Photonic Energy Corporation). The protocol was effective at the time and before the claimed invention was made, and was made as a result of activities undertaken within the scope of the protocol.

Background

The present disclosure relates generally to organic photosensitive optoelectronic devices having squarylium compounds as donor materials. Also disclosed are methods of making these devices, which may include at least one sublimation step for depositing a squaraine compound.

Optoelectronic devices rely on the optical and electronic properties of materials to electronically generate or detect electromagnetic radiation, or to generate electricity from ambient electromagnetic radiation.

Photosensitive optoelectronic devices convert electromagnetic radiation into electricity. Solar cells, also known as Photovoltaic (PV) devices, are a class of photosensitive optoelectronic devices that are particularly useful for generating electricity. PV devices, which can generate electrical energy from sources other than sunlight, can be used to drive electrical consumers to provide, for example, lighting, heating, or to power electronic circuits or devices such as calculators, radios, computers, or remote monitoring or communication equipment. These power generation applications also typically involve charging batteries or other energy storage devices to enable continued operation when direct illumination from the sun or other light source is not available, or to balance the power output of the PV device according to the requirements of a particular application. As used herein, the term "resistive load" refers to any power consuming or storing circuit, apparatus, device or system.

Another type of photosensitive optoelectronic device is a photoconductor. During such operation, the signal detection circuit monitors the impedance of the device to detect changes caused by absorption of light.

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

These three types of photosensitive optoelectronic devices can be distinguished according to the presence or absence of a rectifying junction, defined below, and also according to whether the device is operating using an applied voltage, also referred to as a bias voltage or a bias voltage. Photoconductors do not have rectifying junctions and typically operate using a bias voltage. The PV device has at least one rectifying junction and operates without a bias voltage. The photodetector has at least one rectifying junction and typically, but not always, operates using a bias voltage. Photovoltaic cells typically provide power to circuits, devices or equipment. The photodetector or photoconductor provides a signal or current to control the detection circuit or output information from the detection circuit, but does not provide power to the circuit, device or apparatus.

Photosensitive optoelectronic devices have traditionally been constructed from a variety of inorganic semiconductors, such as crystalline, polycrystalline and amorphous silicon, gallium arsenide, cadmium telluride, and the like. As used herein, the term "semiconductor" refers to a material that is capable of conducting electricity when charge carriers are induced by thermal or electromagnetic excitation. The term "photoconduction" generally refers to the process by which electromagnetic radiation energy is absorbed and converted to excitation energy of charge carriers, such that the carriers are capable of conducting, e.g., transporting, charges in a material. The term "photoconductor" or "photoconductive material" is used herein to refer to semiconductor materials that are selected for their property of absorbing electromagnetic radiation to generate charge carriers.

The properties of PV devices can be described by their efficiency in converting incident solar energy into useful electrical energy. Devices utilizing crystalline or amorphous silicon dominate commercial applications, and some of these have achieved efficiencies of 23% or greater. However, crystal-based devices, particularly large surface area devices, are difficult and expensive to produce due to problems inherent in producing large crystals without significant efficiency-reducing defects. On the other hand, high efficiency amorphous silicon devices still suffer from stability problems. The stable conversion efficiency of currently commercially available amorphous silicon cells is between 4 and 8%. More recent attempts have focused on the use of organic photovoltaic cells to achieve acceptable photovoltaic conversion efficiencies at economical production costs.

The PV device may be optimized to operate under standard illumination conditions (i.e., standard test conditions, which are 1000W/m)²AM1.5 spectral illumination) for maximizing the product of photocurrent times photovoltage. The efficiency of the electrical energy conversion of such a cell under standard illumination conditions depends on the following three parameters: (1) current at zero bias, i.e. short-circuit current I_SCIn amperes; (2) photovoltage at open circuit condition, i.e. open circuit voltage V_OCIn volts; and (3) a fill factor ff.

The PV device, when connected to a load and illuminated with light, produces a photo-generated current. When illuminated under an infinite load, a PV device generates its maximum possible voltage, i.e., the open circuit voltage or V_OC. When illuminated with a short circuit of its electrical contacts, the PV device produces its maximum possible current, i.e. the short circuit current or I_SC. When actually used to generate power, the PV device is connected to a finite resistive load and the power output is given by the product of current and voltage I × V. The maximum total power generated by the PV device must not exceed the product I_SC×V_OC. When the load value is optimized for maximum power extraction, the current and voltage each have a value of I_maxAnd V_max。

The performance index of a PV device is the fill factor, ff, which is defined as:

f＝{I_max V_max}/{I_SC V_OC} (1)

where ff is always less than 1, since in practice I can never be obtained simultaneously_SCAnd V_OC. However, under optimum conditions, when ff is close to 1, the device has a lower series or internal resistance, thus providing a higher percentage of I to the load_SCAnd V_OCThe product of (a). When P is present_incPower efficiency of the device eta when incident power on the device_PCan be calculated from:

η_P＝ff*(I_SC*V_OC)/P_inc。

when electromagnetic radiation of suitable energy is incident on a semiconducting organic material, such as an Organic Molecular Crystal (OMC) material or a polymer, a photon may be absorbed to produce an excited molecular state. This is symbolized by S₀+hvΨS₀ ^*. Where S is₀And S₀ ^*Representing the ground and excited states of the molecule, respectively. This energy absorption is accompanied by an electron lifting from the ground state in the HOMO level, which may be a B-bond, to the LUMO level, which may be B^*-a bond (B)^*Bond), or equivalently, a hole is promoted from the LUMO level to the HOMO level. In organic thin film photoconductors, it is generally believed that the molecular states generated are excitons, i.e., electron-hole pairs in a bound state that are transported as quasi-particles. Excitons may have a considerable lifetime before recombining in pairs, which refers to the process by which the original electron and hole recombine with each other, as opposed to recombining with a hole or electron from another pair. To generate a photocurrent, electron-hole pairs are separated, typically at the donor-acceptor interface between two different contacting organic thin films. If the charges are not separated, they can recombine in a pairwise recombination process, also known as a quenching process, in the form of radiation by emitting light of lower energy than the incident light, or in the form of non-radiation by generating heat. In photosensitive optoelectronic devices, either of these results is undesirable.

Inhomogeneities in the electric field or contacts may cause quenching of the exciton rather than dissociation at the donor-acceptor interface, resulting in no net contribution to current flow. It is therefore desirable to keep the photogenerated excitons away from the contacts. This has the effect of limiting the diffusion of excitons to regions near the junction so that the associated electric field has more opportunity to separate charge carriers released by exciton dissociation near the junction.

In order to generate an internal electric field that occupies a significant volume, it is common practice to juxtapose two layers of material having appropriately selected conductive properties, particularly in terms of the quantum energy state distribution of its molecules. The interface of these two materials is known as a photovoltaic heterojunction. In conventional semiconductor theory, the materials used to form PV heterojunctions are generally referred to as n-type or p-type. Here n-type means that most of the carrier type is electrons. This can be viewed as a material having many electrons in relatively free energy states. p-type means that most of the carrier type is holes. Such materials have many holes in relatively free energy states. The type of background, i.e. the majority carrier concentration that is not photogenerated, depends mainly on unintentional doping by defects or impurities. Impurities and types and concentrations determine the value of the energy gap between the Highest Occupied Molecular Orbital (HOMO) level and the Lowest Unoccupied Molecular Orbital (LUMO) level, referred to as the Fermi energy (Fermi energy) or energy level in the HOMO-LUMO energy gap. Fermi energy describes the statistical occupancy of a quantum energy state of a molecule, expressed in terms of the energy value at which the probability of occupancy equals 1/2. The proximity of the fermi energy to the LUMO energy level indicates that the electron is the dominant carrier. The proximity of the fermi energy to the HOMO energy level indicates that holes are the dominant carriers. Hence, fermi energy is an important qualitative property of conventional semiconductors, and the prototype PV heterojunction is traditionally a p-n interface.

The term "rectifying" especially refers to an interface having asymmetric conductive properties, i.e. an interface supporting charge transport in preferably one direction. Rectification is generally associated with the built-in electric field generated at the heterojunction between appropriately selected materials.

As used herein, and as is generally understood by those skilled in the art, a first "highest occupied molecular orbital" (HOMO) or "lowest unoccupied molecular orbital" (LUMO) energy level is "greater than" or "higher than" a second HOMO or LUMO energy level if the first energy level is closer to the vacuum energy level than the second energy level. Because Ionization Potential (IP) is measured as negative energy relative to vacuum level, a higher HOMO level corresponds to an IP with a smaller absolute value (less negative IP). Likewise, a higher LUMO energy level corresponds to an Electron Affinity (EA) having a smaller absolute value (EA that is less negative). On a conventional energy level diagram, the vacuum level is at the top and the LUMO level of a material is higher than the HOMO level of the same material. The "higher" HOMO or LUMO energy level appears closer to the top of this energy level diagram than the "lower" HOMO or LUMO energy level.

In the case of organic materials, the terms "donor" and "acceptor" refer to the relative positions of the HOMO and LUMO energy levels of two organic materials that are in contact but different. This is in contrast to the use of these terms in the case of inorganic materials, where "donor" and "acceptor" may refer to the dopant types that may be used to create inorganic n-type and p-type layers, respectively. In the case of organic materials, a material is an acceptor if the LUMO level of the material in contact with another material is low. Otherwise, it is the donor. In the absence of an external bias, electrons at the donor-acceptor junction move into the acceptor material, and holes move into the donor material, energetically favorable.

A significant property of organic semiconductors is carrier mobility. Mobility measures the ease with which charge carriers can move through a conductive material in response to an electric field. In the case of organic photosensitive devices, the layer containing materials that tend to conduct by electrons due to high electron mobility may be referred to as an electron transport layer or ETL. A layer containing a material that tends to conduct by holes due to high hole mobility may be referred to as a hole transport layer or HTL. In one embodiment, the acceptor material is ETL and the donor material is HTL.

Conventional inorganic semiconductor PV cells utilize p-n junctions to establish an internal electric field. Early organic thin film cells, such as reported by Tang, appl. phys lett.48, 183(1986), contained heterojunctions similar to those used in conventional inorganic PV cells. However, it is now recognized that in addition to the establishment of the p-n type junctions, the energy level detuning of the heterojunction plays an important role.

Due to photogeneration processes in organic materialsThe fundamental property of (a) is that the energy level detuning at the organic D-a heterojunction is believed to be important for the operation of the organic PV device. Upon photoexcitation of the organic material, localized Frenkel or charge transfer excitons are generated. In order to perform electrical detection or generate an electrical current, the bound excitons must dissociate into their component electrons and holes. Such a process can be induced by a built-in electric field, but the electric field typically found in organic devices (F10)⁶V/cm) is low. The most efficient exciton dissociation in organic materials occurs at the donor-acceptor (D-a) interface. At such an interface, a donor material with a low ionization potential forms a heterojunction with an acceptor material with a high electron affinity. Depending on the energy level arrangement of the donor and acceptor materials, dissociation of the exciton at such an interface may become energetically favorable, producing a free electron polaron in the acceptor material and a free hole polaron in the donor material.

Organic PV cells have many potential advantages over conventional 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 foils. However, organic PV devices typically have relatively low external quantum efficiencies (conversion efficiency of electromagnetic radiation to electrical energy) on the order of 1% or less. This is believed to be due in part to the secondary nature of the inherent light guiding process. That is, carrier generation requires the generation, diffusion, and ionization or collection of excitons. Each of these processes is accompanied by an efficiency η. Subscripts may be used as follows: p denotes power efficiency, EXT denotes external quantum efficiency, a denotes photon absorption exciton generation, ED denotes diffusion, CC denotes collection, and INT denotes internal quantum efficiency. Using this notation:

η_P～η_EXT＝η_A*η_ED*η_CC

η_ExT＝η_A*η_INT

diffusion length (L) of excitons_D)Typically much less than the light absorption lengthA compromise is therefore required between using a thick and therefore high impedance cell with multiple or highly folded interfaces or a thin cell with low light absorption efficiency.

Typically, singlet excitons are formed when light is absorbed in an organic thin film and forms excitons. Singlet excitons may decay to triplet excitons through an intersystem crossing mechanism. Energy is lost in the process, which results in lower efficiency of the device. If energy losses are not to be incurred from intersystem crossing, it is desirable to use materials that generate triplet excitons, since triplet excitons generally have a longer lifetime and therefore a longer diffusion length than singlet excitons.

By using an organometallic material in the photoactive region, the device of the present invention can efficiently utilize triplet excitons. We have found that the singlet-triplet mixing may be so strong for organometallic compounds that absorption involves excitation from the singlet ground state directly to the triplet excited state, eliminating the losses associated with the transition from the singlet excited state to the triplet excited state. The longer lifetime and diffusion length of triplet excitons compared to singlet excitons may allow the use of thicker photoactive regions because triplet excitons may diffuse a longer distance to reach the donor-acceptor heterojunction without sacrificing device efficiency.

Summary of The Invention

Organic photosensitive optoelectronic devices comprising at least one organic heterojunction formed from a squaraine compound and methods of forming the same are described herein. In one embodiment, an organic photosensitive optoelectronic device comprises a squaraine compound of formula I:

wherein Ar is¹And Ar²Each is an optionally substituted aromatic group. As used herein, the term "aromatic group" should be interpreted to generally refer to a cyclic moiety having conjugated double bonds that provide some degree of electronic stabilization. Aromatic compounds are described in detail in Organic Chemistry (Organic Chemistry, 1997 Norton: New York) by Jones, M., Jr. The term "optionally substituted" should be interpreted to mean that each hydrogen atom in the "optionally substituted" moiety may be substituted with a different chemical group (e.g., alkane, halo, hydroxyl, amine, alkylamino, dialkylamino, etc.) so long as the core structure depicted in the formula remains intact.

In one embodiment, the squaraine compound of formula I is 2, 4-bis [4- (N, N-dipropylamino) -2, 6-dihydroxyphenyl or a salt thereof.

In one embodiment, the organic photosensitive optoelectronic device is a solar cell or a photodetector. In another embodiment, the solar cell or photodetector comprises an organic heterojunction. In another embodiment, the organic heterojunction is a donor-acceptor heterojunction, which is formed at the interface of a donor material comprising the squaraine compound of formula I and an acceptor material.

The organic photosensitive optoelectronic device may optionally comprise C₆₀. For example, C may be₆₀Placed in contact with the squaraine compound. As used herein, "C" is₆₀"is intended to mean the molecule Buckminsterfullerene (Buckminsterfullerene), which can be referred to by the IUPAC name (C)₆₀-I_h) Fullerene description.

In one embodiment, the aromatic group (Ar) of the squaric acid compound described in formula I above optionally substituted¹And Ar²) Each independently selected from formula II below:

wherein each X is independently selected from H, alkyl, alkoxy, halo, and hydroxy; and Y is selected from H or an optionally substituted amino group. In another embodiment, each X group of formula II above is a hydroxyl group. As used herein, "independently selected" means that each "X" can vary independently from the other. Of course, they may be the same. In another embodiment, each Y group in formula II above is independently selected from the group consisting of those of formula NR¹R²A group of the formula (I), wherein R¹And R²Each independently is H or an optionally substituted alkyl or aryl group. In another embodiment, the formula NR mentioned above¹R²In, R¹And R²At least one of which is an optionally substituted alkyl group.

As used herein, amino is intended to encompass any salt thereof, such as an acid addition salt. For example, any reference to para-amines also contemplates ammonium salts, and to NR¹R²Any reference to a group or embodiment thereof should be construed as including like salts, such as acid addition salts and the like.

In one embodiment, an organic photosensitive optoelectronic device comprises a squaraine compound of formula III:

wherein each X is independently selected from H, alkyl, alkoxy, halo, and hydroxy; and R is¹And R²Each independently is H or an optionally substituted alkyl or aryl group. In another embodiment, at least one X group of the compounds of formula III above is hydroxy. As stated previously, "independently selected" means that each "X" can vary independently of the other. Of course, they can also be usedMay be identical.

In one embodiment, an organic photosensitive optoelectronic device comprises a squaraine compound of formula I above, wherein Ar is¹And Ar²Each independently selected from the group represented by formula V below:

wherein each of ring A and ring B is optionally substituted C₄-C₈A ring fused to form a bicyclic saturated or unsaturated ring system of 6 to 14 carbon atoms. For example, in one illustrative example, two phenyl rings (each C)₆) Can be fused to form a naphthalene molecule of formula V (C)₁₀)。

In one embodiment of the present invention, the squaric acid compound of formula I is selected from the group consisting of 2, 4-bis [4- (N, N-dipropylamino) -2, 6-dihydroxyphenyl, 2, 4-bis-3-guaiazulenyl-1, 3-dihydroxycyclobutenedinium dihydroxide, 2, 4-bis [4- (N, N-diisobutylamino) -2, 6-dihydroxyphenyl and salts thereof.

In one embodiment, Ar in the compound of formula I¹And Ar²One or two of the groups are independently a group represented by formula VI:

wherein n is selected from 0, 1, 2, 3,4, 5 and 6; and Z represents a linking group. As used herein, the term "linking group" is intended to refer to a chemical group that links the nitrogen atom of the amino group at the 4-position of the group represented by formula VI to its meta position. For example, the linking group can be an alkyl group, an alkenyl group, an amino group, an aromatic group, an ether group, and the like.

It is recognized that the squaric acid compound of formula I may or may not be symmetricalIs symmetrical. As used herein, the term "symmetrical" is intended to include having a symmetry level higher than C_sThe points of the symmetry group are symmetrical.

In one embodiment, a method of forming an organic photosensitive optoelectronic device is provided, the method comprising forming an organic heterojunction by depositing a squaraine compound of formula I on a substrate:

wherein Ar is¹And Ar²Each is an optionally substituted aromatic group. In another embodiment, the substrate comprises at least one electrode or charge transfer layer comprising any sufficiently transparent collector. Non-limiting examples of such transparent collectors include transparent conductive oxides such as Indium Tin Oxide (ITO), Gallium Indium Tin Oxide (GITO), and Zinc Indium Tin Oxide (ZITO).

In one embodiment, the squaraine compound is deposited by sublimation. As used herein, sublimation may include, but is not limited to, vacuum deposition. Thus, sublimation can be carried out at any temperature and pressure suitable for depositing material.

In addition to deposition of squaraine compounds by sublimation, sublimed squaraine compounds may provide certain benefits in purification. It has been found that squaraine that sublimes one or more times provides amorphous films and better properties than non-sublimed films. While not being bound by any theory, it is believed that the multiple sublimation steps function as purification steps, for example, to remove trapped impurities that would otherwise be present, whether the resulting film is amorphous or crystalline.

In one embodiment, the squaric acid compound of formula I is from 0.1 toRate of seconds, e.g. 0.2 toSecond or even 0.2 toA second rate deposition.

In one embodiment, the deposited squaraine compound of formula I hasOr lower thickness, e.g.Or lower thickness, or evenOr a lower thickness. As used herein, "thickness" refers to the thickness of a layer (e.g., the thickness of a layer of squaraine compound), as opposed to the molecular properties (e.g., bond distance) of the material forming any given layer.

It will be appreciated that this material may act as a good donor in any device architecture. Non-limiting examples that may be mentioned for the arrangement of systems in which squarylium materials may be used are selected from planar bulk heterojunctions, hybrid-planar mixed nanocrystalline bulk heterojunctions, and the like. It may be mentioned that the use of this material as C in any device architecture₆₀Good donor of (4).

In another embodiment, the squaraines described herein can also serve as good donors for other acceptors. Furthermore, the disclosed squaraine can even act as an acceptor for a given donor in various device architectures such as those mentioned above, if the energy selection is correct and it transports electrons.

It can be appreciated that the donor-acceptor heterojunction of the present disclosure can comprise at least two different squaraine compounds described herein, e.g., a mixture of two different squaraines. Thus, methods of making such devices comprising mixtures of two or more different squaraines are also described.

In one embodiment, the deposited squaraine compound forms a discontinuous layer. As used herein, the term "discontinuous layer" is intended to refer to a layer that does not have a uniform thickness throughout the layer (e.g., a layer of squarylium compound). In one embodiment, a discontinuous layer of the present invention is a layer that does not completely cover all portions of the layer (or substrate) on which it is deposited, thereby resulting in some portions of the layer being exposed after deposition of the discontinuous layer.

In another embodiment, the deposited squaraine compounds form isolated nano-scale domains. As used herein, "isolated nanoscale domains" are used in contrast to uniform films, and thus refer to the portions of the deposited squaraine compound that exist as 1-50nm domains, forming discontinuous films.

In one embodiment, C is₆₀Is deposited so that it is in contact with the squarylium compound in the organic photosensitive optoelectronic device. In another embodiment, the squaraine layer is ultra-thin, such that C is₆₀In direct contact with the substrate.

In one embodiment, C₆₀The compound is deposited by vacuum deposition, vapor deposition or sublimation.

In another embodiment, C₆₀The layers are deposited by solution processing deposition.

In one embodiment, C₆₀From about 2 to aboutSeconds, e.g.The deposition is performed at a rate of seconds.

In one embodiment, a method of forming an organic photosensitive optoelectronic device comprises depositing CuPc onto a substrate prior to depositing a squaraine compound. In another embodiment, a method of forming an organic photosensitive optoelectronic device includes depositing a layer of an organic compound (e.g., NPD) onto a substrate prior to depositing a squaraine compound to improve performance. Without being bound by any theory, it is believed that this organic compound acts to form a better contact between the squaraine and the ITO anode.

Drawings

Fig. 1 shows an organic PV device comprising an anode, an anode smoothing layer, a donor layer, an acceptor layer, a barrier layer, and a cathode.

FIG. 2 shows a proposed model of charge carrier separation in an exemplary SQ device, confined excitons in SQ phase (white) and C₆₀Bound excitons in phase (black).

Fig. 3 is a schematic energy level diagram of a device having (a) CuPc or (b) SQ as a donor layer. HOMO energy comes from UPS. LUMO energy is measured by Inverse photoemission spectroscopy (IPES), with the exception of SQ, and its LUMO and HOMO energies are determined electrochemically.

FIG. 4 is a graph showing the extinction coefficient of SQ film on quartz and SQ in methylene chloride solution as a function of wavelength.

FIG. 5 isAtomic Force Microscope (AFM) images of squaraine films.

FIG. 6 is a graph showing ITO/CuPc under 1sun AM1.5G simulated illumination (solid line) and in the dark (dashed line)/C₆₀/BCP/Al(Black), ITO/SQ/C₆₀/BCP/Al(triangle) and ITO/C60/BCP/AlGraph of the J-V characteristics of the (circles).

FIG. 7 is a graph showing ITO/CuPc after 1 hour of testing at 1sun under AM1.5G simulated sunlight (solid line) and in the dark (dashed line)/C₆₀/BCP/Al(Black), ITO/SQ/C₆₀/BCP/Al(triangular) device and ITO/SQ/C₆₀/BCP/AlGraph of the J-V characteristics of the (circles).

FIG. 8 is a graph showing ITO/SQ at 1sun under AM1.5G simulated sunlight (solid line) and in the dark (dashed line)/C₆₀/BCP/Al[ SQ Rate <)Second, black]、ITO/SQ/C₆₀/BCP/Al[ SQ rate &Second, square]A graph of J-V characteristics of (1).

FIG. 9 is a comparison of external quantum efficiency curves for two SQ devices each having a different C₆₀Deposition rate: a) c₆₀Deposition rateSecond (black); b) c₆₀Deposition rateSeconds (square).

FIG. 10 is a graph showing the simulated solar illumination at AM1.5G at 1sun (solid line) and in the dark (dashed line) with ITO/SQ/C₆₀/BCPArchitecture of/Al, J-V characteristics of SQ devices with various SQ thicknesses (marked by variable x): 1) x is 50 (black); 2) x ═ 65 (square); 3) x ═ x75 (triangle) and 4) x 100 (circle).

Figure 11 shows external quantum efficiency plots for SQ devices with the following architecture: ITO/SQ/C₆₀/BCP/Al(ii) a And ITO/SQ/CuPC60/BCP/Al

Fig. 12 depicts the chemical structure of copper phthalocyanine (CuPc).

FIG. 13 is an ITO/CuPc/C₆₀/BCP/Al

a) x is 50 (black); b) x is 100 (square); c) x 200 (circular) and ITO/SQ/CuPc/C₆₀/BCP/AlExternal quantum efficiency plot of (triangles).

FIG. 14 is a graph of 1sun with ITO/CuPc under AM1.5G simulated sunlight (solid line) and in the dark (dashed line) with ITO/CuPc/SQ/C₆₀/BCPJ-V signature plot for SQ device for/Al architecture: 1) x ═ 65 (black); 2) x 130 (square); 3) x 180 (triangle) and 4) x 0 (circle).

FIG. 15 is a schematic energy level diagram of NPD, SQ, C60 and BCP. HOMO energy is from UPS and LUMO energy is from IPES measurements, except SQ and NPD, whose LUMO and HOMO energies are determined electrochemically.

Figure 16 shows the chemical structure of N, N '-di-1-naphthyl-N, N' -diphenyl-1, 1 '-biphenyl-4, 4' diamine (NPD) in its free base form.

FIG. 17 is (a) ITO/NPD/SQ/C₆₀/BCP/Al(black), (b) ITO/NPD/C₆₀/BCP/Al(Square) and (c) ITO/CuPc/SQ/C₆₀/BCP/AlExternal quantum efficiency plot of (circular).

Figure 18 is a schematic diagram of a possible architecture for a SQ-containing device made in accordance with the present disclosure.

Figure 19 is a graph showing current density as a function of potential for spin-cast SQ devices fabricated in accordance with the present disclosure.

Detailed Description

The present disclosure relates to organic photosensitive optoelectronic devices. The organic devices of embodiments of the present invention can be used, for example, to generate usable current from incident electromagnetic radiation (e.g., PV devices), or can be used to detect incident electromagnetic radiation. Embodiments of the invention may include an anode, a cathode, and a photoactive region between the anode and the cathode. The photoactive region is the portion of the photosensitive device that absorbs electromagnetic radiation to generate excitons that may dissociate to generate an electrical current. The organic photosensitive optoelectronic device may further comprise at least one transparent electrode to allow incident radiation to be absorbed by the device. Several PV device materials and configurations are described in U.S. patent nos. 6,657,378, 6,580,027, and 6,352,777, which are incorporated herein by reference in their entirety.

Fig. 1 shows an organic photosensitive optoelectronic device 100. The figures are not necessarily to scale. Device 100 can include substrate 110, anode 115, anode smoothing layer 120, donor layer 125, acceptor layer 130, barrier layer 135, and cathode 140. Cathode 140 can be a compound cathode having a first conductive layer and a second conductive layer. Device 100 may be fabricated by depositing the described layers in sequence. Charge separation may occur primarily at the organic heterojunction between the donor layer 125 and the acceptor layer 130. The built-in potential at the heterojunction is determined by the HOMO-LUMO energy level difference between the two materials that contact each other to form the heterojunction. The HOMO-LUMO gap offset between the donor and acceptor materials creates an electric field at the donor/acceptor interface that promotes charge separation of excitons generated within the exciton diffusion length at the interface.

The particular arrangement of layers shown in fig. 1 is merely exemplary and not intended to be limiting. For example, certain layers (e.g., barrier layers) may be omitted. Other layers (e.g., reflective layers or additional acceptor and donor layers) may be added. The order of the layers may be changed. Other arrangements than those specifically described may be used.

The substrate can be any suitable substrate that can provide the desired structural properties. The substrate may be flexible or rigid, planar or non-planar. The substrate may be transparent, translucent or opaque. Plastics and glass are examples of rigid substrate materials that may be used herein. Plastic and metal foils are examples of flexible substrate materials that can be used in the present disclosure. The material and thickness of the substrate can be selected to achieve desired structural and optical properties.

U.S. Pat. No.6,352,777, incorporated herein by reference, provides examples of electrodes or contacts that may be used in photosensitive optoelectronic devices. As used herein, the terms "electrode" and "contact" refer to a layer that provides a medium for delivering a photogenerated current to an external circuit or for providing a bias voltage to a device. That is, electrodes or contacts provide an interface between an active region of an organic photosensitive optoelectronic device and a wire, lead, trace or other means for transporting charge carriers to or from an external circuit.

In photosensitive optoelectronic devices, it is desirable to have a maximum amount of ambient electromagnetic radiation from outside the device enter the optically active interior region. That is, the electromagnetic radiation must reach the photoconductive layer where it can be converted to electricity by photoconductive absorption. This generally requires that at least one electrical contact should minimally absorb and minimally reflect incident electromagnetic radiation. That is, such contacts should be substantially transparent. The opposite electrode may be a reflective material to reflect light that passes through the cell without being absorbed back through the cell.

As used herein, a layer of material, or several layers of a series of different materials, is said to be "transparent" when at least 50% of the relevant wavelength of ambient electromagnetic radiation is allowed to be transmitted through the layer. Likewise, a layer that allows transmission of some, but less than 50%, of the relevant wavelengths of ambient electromagnetic radiation is said to be "translucent".

As used herein, "top" refers to furthest away from the substrate, while "bottom" refers to closest to the substrate. For example, for a device having two electrodes, the bottom electrode is the electrode closest to the substrate, and is typically the first fabricated electrode. The bottom electrode has two surfaces, a bottom surface closest to the substrate and a top surface further from the substrate. When a first layer is described as being "disposed over" a second layer, the first layer is disposed further away from the substrate. Other layers may be present between the first and second layers, unless it is specified that the first layer is "in physical contact with" the second layer. For example, a cathode may be described as "disposed over" an anode, although various organic layers are present therebetween.

In one embodiment, the electrodes are comprised of a metal or "metal substitute. The use of the term "metal" herein encompasses both materials composed of an elemental pure metal, such as Mg, and metal alloys, which are materials known as Mg: Ag composed of two or more elemental pure metals, such as Mg and Ag, together. As used herein, the term "metal substitute" refers to a material that is not a metal within the scope of the specification definition, but that has metal-like properties that are desirable in certain specific applications. Commonly used metal alternatives for electrodes and charge transport layers include doped wide bandgap semiconductors such as transparent conducting oxides such as Indium Tin Oxide (ITO), Gallium Indium Tin Oxide (GITO) and Zinc Indium Tin Oxide (ZITO).

ITO is a highly doped degenerate n + semiconductor with an optical bandgap of about 3.2eV, making it transparent to wavelengths greater than about 390 nm. Another suitable metal substitute is the transparent conductive polymer Polyaniline (PANI) and its chemical relatives. The metal substitute may also be selected from a wide range of non-metallic materials, wherein the term "non-metallic" is meant to cover a wide range of materials, as long as the material does not contain the metal in chemically uncombined form. When a metal is present in its chemically uncombined form, alone or in combination with one or more other metals, as an alloy, the metal may also be referred to as being present in its metallic form or as being "free metal". Thus, the metal substitute electrodes of the present invention may sometimes be referred to as "metal-free," where the term "metal-free" is expressly meant to encompass materials that are free of metals in chemically unbound form.

Free metals typically have a metal bonding form resulting from a large number of valence electrons that move freely in the electron conduction band throughout the metal lattice. While metal substitutes may contain metallic constituents, they are "non-metallic" in terms of several aspects. They are not pure free metals, nor are they alloys of free metals. When metals are present in their metallic form, the electron conduction band tends to provide, among other metallic properties, high conductivity and high reflectivity to optical radiation.

As one or more transparent electrodes of a photosensitive optoelectronic device, embodiments of the present invention can include a highly transparent, non-metallic, low-impedance cathode, such as disclosed in U.S. Pat. No.6,420,031 to Parthasarathy et al ("Parthasarathy '031"), or a high-efficiency, low-impedance metal/non-metallic compound cathode, such as disclosed in U.S. Pat. No.5,703,436 to Forrest et al ("Forrest' 436"), both of which are incorporated herein by reference in their entirety. Each type of cathode can be prepared in a manufacturing process that includes sputter deposition of an ITO layer on an organic material, such as copper phthalocyanine (CuPc), to form a highly transparent, non-metallic, low-impedance cathode, or on a thin Mg: Ag layer to form a high-efficiency, low-impedance metal/non-metallic compound cathode. Parthasarathy' 031 discloses that the ITO layer on which the organic layer is deposited, rather than the organic layer on which the ITO layer is deposited, does not function as an effective cathode. For PV, ITO will be deposited onto the substrate unless the layers are deposited in the opposite direction.

In addition to CuPc, an organic compound (e.g., NPD) that promotes the formation of a crystalline or amorphous thin film may be utilized as a hole transport material between the anode (e.g., ITO) and SQ. The organic compounds that promote the thin film do not contribute to photon absorption and have suitable energy chemistry with SQ. When with C₆₀When used simultaneously, the presence of the organic compound layer for promoting the film can ensure C₆₀Does not contact ITO, thereby preventing C₆₀Loss of the intrinsic photocurrent. Further, the organic compound that promotes the thin film does not trap charges according to its known good hole mobility. In one embodiment of the present invention, the following device structure is fabricated: ITO/NPD/SQ/C₆₀/BCP/AlThe thickness of the NPD layer can be varied to optimize performance of the SQ device. For example, the NPD layer may be smaller thanIs less thanOr less thanIn one embodiment, the NPD layer is

The chemical structure of NPD is shown in figure 16. In the context of the present application, NPD is not limited to the free base form only and may thus include, for example, any salt of NPD, including mono-and/or di-acid addition products.

Herein, the term "cathode" is used in the following manner. In a non-stacked PV device or a single unit of stacked PV devices, such as a PV device, electrons move from the photoconductive material to the cathode under ambient radiation in conjunction with a resistive load and in the absence of an applied voltage. Likewise, the term "anode" as used herein refers to the movement of holes from the photoconductive material to the anode under illumination in a PV device, which is equivalent to the movement of electrons in the opposite manner. It should be noted that when the term is used herein, the anode and cathode may be electrodes or charge transfer layers.

An organic photosensitive device will comprise at least one photoactive region in which light is absorbed to form excited states or "excitons" which may subsequently dissociate into electrons and holes. Dissociation of the excitons typically occurs at the heterojunction formed by juxtaposing the acceptor layer and the donor layer. For example, in the device of fig. 1, the "optically active region" may include a donor layer 125 and an acceptor layer 130.

The acceptor material may comprise, for example, perylene, naphthalene, fullerene, or nanotubes. An example of an acceptor material is 3,4, 9, 10-perylenetetracarboxylic bis-benzimidazole (PTCBI). Alternatively, the receptor layer may comprise a fullerene material as described in U.S. Pat. No.6,580,027, which is incorporated herein by reference in its entirety. Adjacent to the acceptor layer is a layer of organic donor-type material. The boundary of the acceptor layer and the donor layer forms a heterojunction, which can generate an endogenous electric field. The material of the donor layer may be phthalocyanine or porphyrin, or derivatives or transition metal complexes thereof such as copper phthalocyanine (CuPc). Other suitable acceptor and donor materials may be used. As used herein, one donor material of particular importance to the present invention is the squarylium compound of formula I below:

wherein Ar is¹And Ar²Each is an optionally substituted aromatic group. Such compounds may be used alone or in combination with other donor materials. All references to compounds of formula I, including, for example, devices and methods comprising compounds of formula I, are intended to encompass any salts or derivatives of such compounds. For example, one skilled in the art will recognize that the compounds of formula I may exist in the form of ketones or alcohols in addition to the charge separated forms depicted.

In one embodiment of the invention, the stacked organic layers include one or more Exciton Blocking Layers (EBLs), as described in U.S. Pat. No.6,097,147, Peumans et al, Applied Physics Letters 2000, 76, 2650-52, and co-pending patent application Ser. No. 09/449,801 filed on 26.11.1999, both of which are incorporated herein by reference. By including EBLs to confine the photogenerated excitons in the region near the dissociation interface and to prevent quenching of the parasitic excitons at the photoactive organic/electrode interface, higher internal and external quantum efficiencies are obtained. In addition to limiting the volume in which excitons can diffuse, EBLs can also act as diffusion barriers to species introduced during electrode deposition. In some cases, EBLs can be made thick enough to fill pinholes or short defects that would otherwise render the organic PV device inoperable. Thus, the EBL may help protect the fragile organic layers from damage that may occur when depositing electrodes on the organic material. The EBL can also act as an optical spacer, allowing the optical field peaks to be focused in the active region of the cell.

It is believed that the exciton blocking properties of EBLs result from their LUMO-HOMO energy gap being significantly larger than that of the adjacent organic semiconductor in which the exciton is blocked. Thus, due to energy considerations, the confined excitons cannot exist in the EBL. While it is desirable for the EBL to block excitons, it is not desirable for the EB to block all charges. However, EBLs may block charge carriers of one sign due to the nature of adjacent energy levels. In design, an EBL will be present between two other layers, typically an organic photosensitive semiconductor layer and an electrode or charge transfer layer or charge recombination layer. Adjacent electrodes or charge transfer layers will be located before and after the cathode or anode. Thus, the material used for the EBL in a given location of the device will be selected such that the transport of carriers of the desired sign to or from the electrodes or charge transfer layers is not hindered. The correct energy level alignment ensures that there is no barrier to charge transport, preventing an increase in series resistance. For example, for a material used as a cathode side EBL, it is desirable to have a LUMO energy level that closely matches the LUMO energy level of the adjacent ETL material in order to minimize unwanted blocking of electrons.

It should be appreciated that the exciton blocking properties of a material are not intrinsic to its HOMO-LUMO energy gap. Whether a given material will act as an exciton barrier depends on the relative HOMO and LUMO energy levels of the adjacent organic photoactive materials. Thus, it is not possible to identify a class of compounds in isolation as exciton blockers regardless of the context in which they may be used in a device. However, based on the teachings herein, one skilled in the art can identify whether a given material will function as an exciton blocking layer when used with a selected group of materials in the construction of an organic PV device.

In one embodiment of the invention, the EBL is located between the receptor layer and the cathode. One material for the EBL comprises 2, 9-dimethyl-4, 7-diphenyl-1, 10-phenanthroline (also known as bathocuproine or BCP), which is believed to have a LUMO-HOMO level separation of about 3.5eV, or bis (2-methyl-8-hydroxyquinoline) -aluminum (III) phenolate (Alq)₂OPH). BCP is an effective exciton barrier that can readily transport electrons from the acceptor layer to the cathode.

The EBL layer may be doped with suitable dopants including, but not limited to, 3,4, 9, 10-perylenetetracarboxylic dianhydride (PTCDA), 3,4, 9, 10-perylenetetracarboxylic diimine (PTCDI), 3,4, 9, 10-perylenetetracarboxylic-bis-benzimidazole (PTCBI), 1, 4, 5, 8-naphthalene tetracarboxylic dianhydride (NTCDA), and derivatives thereof. The BCP deposited in the devices of the invention is believed to be amorphous. The apparently amorphous BCP exciton blocking layers of the present invention can exhibit particularly rapid film recrystallization at high light intensities. The resulting morphological change to polycrystalline material produces a lower quality film with possible defects such as shorts, voids or sinks of electrode material.

Thus, it has been found that the incorporation of suitable, relatively large and stable molecules into certain EBL materials, such as BCP, that exhibit such defects can stabilize the EBL structure against morphological changes that cause performance degradation. It should also be appreciated that incorporating a material with a LUMO energy level close to the EBL into the EBL that transports electrons in a given device will help ensure that electron traps are not formed that could create space charge accumulation and degrade performance. Furthermore, it should be appreciated that a relatively low doping density will minimize exciton generation at isolated dopant sites. This absorption reduces the photoconversion efficiency of the device because the surrounding EBL material effectively inhibits diffusion of these excitons.

Representative embodiments may also include a transparent charge transport layer or charge recombination layer.

As described herein, charge transport layers differ from acceptor and donor layers by the fact that charge transport layers are typically, but not necessarily, inorganic (typically metals) and they may be selected to be not photoconductive active. The term "charge transport layer" is used herein to refer to a layer that is similar to an electrode but different in that the charge transport layer transports charge carriers from only one small portion of the optoelectronic device to an adjacent small portion. The term "charge recombination layer" is used herein to refer to a layer similar to an electrode but different in that the charge recombination layer allows recombination of electrons and holes between adjacent charge carrier layers and may also enhance the internal optical field strength near the active layer or layers. The electrically load carrying bonding layer may be comprised of translucent metal nanoclusters, nanoparticles, or nanorods as described in U.S. patent No.6,657,378, which is incorporated herein by reference in its entirety.

In another embodiment of the invention, an anode smoothing layer is located between the anode and the donor layer. One material for this layer comprises a film of 3, 4-polyethylenedioxythiophene polystyrene sulfonate (PEDOT: PSS). Introduction of a PEDOT: PSS layer between the anode (ITO) and the donor layer (CuPc) can result in a significant increase in manufacturing yield. Without being bound by any theory, it is believed that the increase in manufacturing yield is a result of the ability of spin-coated PEDOT: PSS films to planarize ITO, which otherwise may create short circuits through the molecular layers of the film.

In another embodiment of the invention, one or more layers may be treated with a plasma prior to deposition of the next layer. The layer may be treated with, for example, a mild argon or oxygen plasma. This treatment is beneficial because it reduces the series resistance. It is particularly advantageous to subject the PEDOT: PSS layer to a mild plasma treatment before the deposition of the next layer.

The simple layered structure shown in fig. 1 is provided merely as a non-limiting example, and it should be understood that embodiments of the present invention may be used with a wide variety of other structures. The specific materials and structures described are exemplary in nature, and other materials and structures may be used. Combining the various layers in different ways can result in a functional organic photosensitive optoelectronic device, or certain layers can be omitted entirely depending on design, performance, and cost considerations. Other layers not specifically described may also be included. Although many of the examples provided herein describe the various layers as comprising a single material, it should be understood that combinations of materials, such as mixtures of host and dopant or more generally mixtures, may be used. Further, the layer may have various sub-layers. The names provided for the various layers herein are not intended to be strictly limiting. Organic layers that are not part of the optically active region, i.e., organic layers that do not generally absorb photons and contribute significantly to photocurrent, may be referred to as "non-photoactive layers". Examples of non-photoactive layers include EBLs and anode smoothing layers. Other types of non-photoactive layers may also be used.

Non-limiting examples of organic materials for use in the photoactive layer of a photosensitive device include cyclometallated organometallic compounds. As used herein, the term "organometallic" is as generally understood by those skilled in the art, and as given, for example, in Inorganic Chemistry (second edition), by Gary l.miesler and Donald a.tarr (innovative Chemistry, Prentice Hall (1998)). Thus, the term organometallic refers to a compound having an organic group bonded to a metal through a carbon-metal bond. This category does not include, by itself, coordination compounds, which are substances having only donor bonds from heteroatoms, such as metal complexes of amines, halides, pseudohalides (CN, etc.), and the like.

In practice, the organometallic compound typically contains one or more donor bonds from the heteroatom in addition to one or more carbon-metal bonds to the organic group. The carbon-metal bond to an organic group refers to a direct bond between a metal and a carbon atom of an organic group such as phenyl, alkyl, alkenyl, etc., but does not refer to a metal bond to a carbon of an "inorganic carbon" such as CN or CO. The term cyclometallated refers to compounds comprising a bidentate organometallic ligand such that upon bonding to a metal a ring structure is formed comprising the metal as one of the ring members.

The organic layer may be fabricated using vacuum deposition, solution processing, organic vapor deposition, inkjet printing, and other means known in the art. As used herein, solution processing includes spin coating, spray coating, dip coating, blade coating, and other techniques known in the art.

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

This result can be achieved by considering several criteria that can be used for layer thickness selection. For exciton diffusion length L_DIt is desirable to be greater than or comparable to the layer thickness L, since it is believed that most exciton dissociation will occur at the interface. If L is_DLess than L, then many excitons may recombine before dissociation. Furthermore, it is desirable for the total thickness of the photoconductive layer to be on the order of 1/α of the electromagnetic radiation absorption length, where α is the absorption coefficient, so that nearly all radiation incident on the PV device is absorbed for the generation of excitons. Furthermore, the thickness of the photoconductive layer should be as thin as possible to avoid excessive series resistance caused by the high bulk resistance of the organic semiconductor.

These competing criteria therefore inherently require a compromise in the selection of the photoconductive organic layer thickness of the photosensitive photovoltaic cell. Thus, on the one hand, a thickness (for a single cell device) comparable to or greater than the absorption length is required in order to absorb the maximum amount of incident radiation. On the other hand, as the thickness of the light guide layer increases, two undesirable effects also increase. One is that increasing the thickness of the organic layer will increase the device resistance and decrease the efficiency due to the high series resistance of the organic semiconductor. Another unwanted effect is that increasing the photoconductive layer thickness will increase the probability that excitons will be generated at an effective field away from the charge separation interface, resulting in an increase in the probability of pairwise recombination and likewise a decrease in efficiency. Therefore, a device configuration that balances these competing effects in a manner that can produce high external quantum efficiencies for the overall device is desirable.

The organic photosensitive optoelectronic devices of the present invention can function as photodetectors. In such an embodiment, the device may be a multilayer organic device, such as described in U.S. patent application serial No.10/723,953 filed on 26.11.2003, which is hereby incorporated by reference in its entirety. In this case, an external electric field may be generally applied to facilitate extraction of the separated charges.

A concentrator or trapping configuration may be used to increase the efficiency of an organic photosensitive optoelectronic device in which photons are forced multiple times through a thin absorbing region. U.S. Pat. Nos. 6,333,458 and 6,440,769, which are incorporated herein by reference in their entirety, address this problem by using structural designs that improve the light conversion efficiency of photosensitive optoelectronic devices by optimizing the optical geometry to achieve high absorption and use with light concentrators that improve collection efficiency. This geometry for the photosensitive device significantly increases the optical path through the material by trapping incident radiation within a reflective cavity or light guiding structure and thereby recycling it by reflecting it multiple times through the photo-responsive material. Thus, the geometries disclosed in U.S. Pat. Nos. 6,333,458 and 6,440,769 improve the external quantum efficiency of the device without causing a significant increase in bulk resistance. The device geometry includes a first reflective layer; a transparent insulating layer, which should be longer than the optical coherence length of the incident light in all dimensions, to prevent optical interference effects of the microcavity; a first transparent electrode layer adjacent to the transparent insulating layer; a photosensitive heterostructure adjacent to the transparent electrode; and a second electrode also having reflectivity.

In one embodiment, one or more coatings may be used to focus the optical energy in a desired region of the device. See, for example, U.S. patent No.7,196,835, U.S. patent application No.10/915,410, the disclosures of which, particularly in relation to such coatings, are incorporated herein by reference.

Various devices fabricated in accordance with the above disclosure were fabricated and tested. Specifically, changes in SQ layer thickness and the presence and/or thickness of the hole transport layer were measured under 1sun am1.5g simulated solar irradiation (uncorrected). The results of these tests are provided in tables 1 and 2 below.

Table 1. structure and photovoltaic data for devices containing at least one SQ donor or CuPc hole transport layer.

Table 2. structure and photovoltaic data for devices containing at least one SQ donor or NPD hole transport layer.

As shown, the present inventors have found that squarylium materials are beneficial when used in photovoltaic devices made by organic vapor deposition techniques. The inventors have also discovered an alternative method of processing squaraine-based PV cells by solution chemistry, for example by spin coating. Taking advantage of the fact that squaric acid is a good dye that is soluble in most chlorine-containing solvents, the present inventors have used solution chemistry to process squaric acid-based PV cells, which have comparable performance characteristics to devices fabricated by vapor deposition techniques. One advantage of using solution chemistry to process the devices of the present invention is the ability to use more squaraine, since the same amount of squaraine is impractical when typically used in vapor deposition techniques because of decomposition after sublimation.

Other embodiments of the devices and methods described herein will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope of the described devices and methods being indicated by the following claims.

Example (b): solution treated squarylium/C60 bi-layer photovoltaic cell

In the present embodimentUsing 2, 4-bis [4- (N, N-diisobutylamino) -2, 6-dihydroxyphenyl]Squaric acid (SQ) molecule. The device structure includes: ITO/spin-cast SQ/C₆₀/BCP/AlThe thickness of spin-cast SQ films was controlled by the solution concentration of SQ in Dichloromethane (DCM) solvent. By dissolving 3mg SQ in 2ml DCM solvent, a SQ solution with a concentration of 1.5mg/ml was obtained. The SQ solution was spin-coated on the previously cleaned ITO by spin-coating at a spin rate of 3000rpm for 40 seconds in airSpin-cast SQ film. Next, C is placed under high vacuum₆₀BCP and AL cathodes were deposited on the spin-cast film.

The SQ devices fabricated according to this example were tested by irradiating them under 1sun AM1.5G simulated sunlight. The results of this test are reported in table 3.

TABLE 3 Structure and photovoltaic data for solution processed SQ devices illuminated under 1sun AM1.5G simulated sunlight

Unless otherwise indicated, all numbers expressing quantities of ingredients, reaction conditions, and so forth used in the specification and claims are to be understood as being modified in all instances by the term "about". Accordingly, unless indicated to the contrary, the numerical parameters set forth in the specification and claims are approximations that may vary depending upon the desired properties sought to be obtained by the present invention.

Other embodiments of the invention will be apparent to those skilled in the art from consideration of the specification and practice of the invention disclosed herein. It is intended that the specification and examples be considered as exemplary only, with a true scope and spirit of the invention being indicated by the following claims.

Claims (38)

1. An organic photosensitive optoelectronic device comprising at least one donor-acceptor heterojunction formed from a squaraine compound of formula I:

wherein Ar is¹And Ar²Each independently selected from optionally substituted aromatic groups.

2. The organic photosensitive optoelectronic device of claim 1, wherein Ar is Ar¹And Ar²Each independently selected from the group of formula II:

wherein each X is independently selected from H, alkyl, alkoxy, halo, and hydroxy; and is

Y is selected from H or an optionally substituted amino group.

3. The organic photosensitive optoelectronic device of claim 2, wherein at least one X group of formula II is a hydroxyl group.

4. The organic photosensitive optoelectronic device of claim 2, wherein each Y group is independently selected from the group consisting of formula NR¹R²A group of the formula (I), wherein R¹And R²Each independently selected from H or an optionally substituted alkyl or aryl group.

5. The organic photosensitive optoelectronic device of claim 4, wherein R¹And R²At least one of which is a substituted alkyl group.

6. The organic photosensitive optoelectronic device of claim 1, wherein the squaraine compound is represented by formula III:

wherein each X is independently selected from H, alkyl, alkoxy, halo, and hydroxy; and R is¹And R²Each independently selected from optionally substituted alkyl or aryl.

7. The organic photosensitive optoelectronic device of claim 6, wherein at least one X group of the compound of formula III is a hydroxyl group.

8. The organic photosensitive optoelectronic device of claim 1, wherein the device is a solar cell or a photodetector.

9. The organic photosensitive optoelectronic device of claim 8, wherein the device is a solar cell, and wherein the at least one donor-acceptor heterojunction is formed at an interface of a material comprising the squaraine compound of formula I and a material selected from a donor or an acceptor.

10. The organic photosensitive optoelectronic device of claim 1, further comprising at least one electrode or charge transfer layer comprising a transparent collector.

11. The organic photosensitive optoelectronic device of claim 10, further comprising a buffer layer between the transparent conductive oxide and the squaraine.

12. The organic photosensitive optoelectronic device of claim 11, wherein the buffer layer comprises at least one of copper phthalocyanine (CuPc) and N, N '-di-1-naphthyl-N, N' -diphenyl-1, 1 '-biphenyl-4, 4' diamine (NPD).

13. The organic photosensitive optoelectronic device of claim 12, further comprising C in close proximity to the squaraine compound₆₀And (3) a layer.

14. The organic photosensitive optoelectronic device of claim 1, wherein Ar is Ar¹And Ar²Each independently selected from the group represented by formula V:

wherein each of ring A and ring B is optionally substituted C₄-C₈Ring, fused theretoForm a bicyclic saturated or unsaturated ring system containing 6 to 14 carbon atoms.

15. The organic photosensitive optoelectronic device of claim 14, wherein the squaraine compound of formula I is selected from the group consisting of 2, 4-bis-3-guaiazulenyl-1, 3-dihydroxycyclobutenediium dihydroxide and salts thereof.

16. The organic photosensitive optoelectronic device of claim 1, wherein the squaraine compound of formula I is selected from the group consisting of 2, 4-bis [4- (N, N-dipropylamino) -2, 6-dihydroxyphenyl, 2, 4-bis [4- (N, N-diisobutylamino) -2, 6-dihydroxyphenyl, and salts thereof.

17. The organic photosensitive optoelectronic device of claim 1, wherein Ar is Ar¹And Ar²Each independently selected from the group represented by formula VI:

wherein n is selected from 0, 1, 2, 3,4, 5 and 6; and Z represents a linking group.

18. The organic photosensitive optoelectronic device of claim 1, wherein the squaraine compound of formula I is not symmetric.

19. The organic photosensitive optoelectronic device of claim 1, wherein the squaraine compound of formula I is amorphous.

20. The organic optoelectronic device of claim 19, wherein the donor-acceptor heterojunction is formed from at least two different squaraine compounds.

21. The organic optoelectronic device of claim 1, wherein the donor-acceptor heterojunction is a mixed heterojunction or a bulk heterojunction.

22. A method of forming an organic photosensitive optoelectronic device, the method comprising forming at least one donor-acceptor heterojunction formed from a squaraine compound of formula I:

wherein Ar is¹And Ar²Each independently selected from optionally substituted aromatic groups.

23. The method of claim 22, wherein the substrate further comprises at least one electrode or charge transfer layer comprising a transparent current collector.

24. The method of claim 23, wherein the squaraine compound is deposited by one or more methods selected from the group consisting of vacuum deposition and solution treatment.

25. The method of claim 24, wherein the solution processing comprises one or more techniques selected from spin coating, spray coating, dip coating, or knife coating.

26. The method of claim 24, wherein the squaraine compound is sublimed one or more times during vacuum deposition.

27. The method of claim 22, wherein the squaraine compound of formula I is from 0.1 toIs deposited.

28. The method of claim 22, wherein the deposited squaraine compound of formula I hasOr a lower thickness.

29. The method of claim 22, further comprising depositing C on the squaraine compound by vacuum deposition or vapor deposition₆₀。

30. The method of claim 29, wherein the donor-acceptor heterojunction is a mixed heterojunction or a bulk heterojunction.

31. The method of claim 29, wherein said C₆₀In direct contact with the substrate at least at one point.

32. The method of claim 31, wherein C₆₀From 2 toIs deposited.

33. The method of claim 22, further comprising depositing at least one layer of CuPc or NPD onto the substrate prior to depositing the squaraine compound.

34. The method of claim 33, wherein said CuPc is deposited with squaraine to form a layer comprising a mixture of squaraine and CuPc.

35. The method of claim 22, wherein depositing the squaraine compound forms a discontinuous layer.

36. The method of claim 22, comprising depositing two or more different squaraine films to form the donor-acceptor heterojunction.

37. An organic photosensitive optoelectronic device comprising at least one donor-acceptor heterojunction formed from a mixture of at least two different squaraines comprising a compound of formula I:

wherein Ar is¹And Ar²Each independently selected from optionally substituted aromatic groups.

38. The organic photosensitive optoelectronic device of claim 37, wherein the mixture of at least two different squaraines comprises at least one squaraine selected from the group consisting of: 2, 4-bis [4- (N, N-dipropylamino) -2, 6-dihydroxyphenyl, 2, 4-bis-3-guaiazulenyl-1, 3-dihydroxycyclobutenediylium dihydroxide, 2, 4-bis [4- (N, N-diisobutylamino) -2, 6-dihydroxyphenyl, and salts thereof.