WO2010139782A1 - Light-absorbing organic component - Google Patents

Abstract

The invention relates to a light-absorbing organic component, in particular an organic photovoltaic solar cell, having a contact and a mating contact as well as a region of organic material(s) which is electrically connected to the contact and to the mating contact, wherein a photoactive region with a photoactive heterojunction between a hole-conducting organic material and an electron-conducting organic material is formed in the organic region.

Description

 Light absorbing organic device

The invention relates to a light-absorbing organic component, in particular an organic photovoltaic solar cell having a contact and a mating contact and a region of organic material or organic materials, which is electrically connected to the contact and the mating contact, wherein in the organic region, a photoactive region with a photoactive heterojunction is formed between a hole-conducting organic material and an electron-conducting organic material.

The research and development of organic solar cells has increased sharply, especially in the last ten years. The maximum efficiency reported so far for so-called "small molecules" is 5.7% [Jiangeng Xue, Soichi Uchida, Barry P. Rand, and Stephen R. Forrest, Appl. Phys. Lett. 85 (2004) 5757]. Among small molecules For the purposes of the present invention, non-polymeric organic, monodisperse molecules in the mass range between 100 and 2000 grams / mole are understood, which has hitherto not been able to achieve the typical efficiencies of 10-20% for inorganic solar cells, but organic solar cells are subject to the same physical limitations such as inorganic solar cells, which is why, after appropriate development work at least theoretically similar efficiencies are expected.

Organic solar cells consist of a sequence of thinner ones

Layers (which are typically each one to one micron thick) of organic materials, which are preferably vapor-deposited in vacuum or spin-coated from a solution. The electrical contacting can be achieved by metal layers, transparent conductive oxides (TCOs) and / or transparent conductive polymers (PEDOT-PSS, PANI) take place.

A solar cell converts light energy into electrical energy. In this sense, the term "photoactive" is understood here, namely the conversion of light energy into electrical energy. In contrast to inorganic solar cells, solar cells do not directly generate free charge carriers by light, but excitons are first formed, ie electrically neutral excitation states (bound electron-hole pairs). Only in a second step, these excitons are separated into free charge carriers, which then contribute to the electric current flow.

The advantage of such organic-based devices over conventional inorganic-based devices (semiconductors such as silicon, gallium arsenide) is the sometimes extremely high optical absorption coefficients (up to 2 × 10 ⁵ cm ^-1 ), which allow efficient absorber layers of just a few nanometers Thickness produce, so that offers the opportunity to produce very thin solar cells with low material and energy costs. Further technological aspects are the low costs, the organic semiconductor materials used being very cost-effective when produced in large quantities; the possibility of producing flexible large-area components on plastic films, and the almost unlimited possibilities of variation and the unlimited availability of organic chemistry.

Since no high temperatures are required in the production process (substrate temperatures of a maximum of 110 ^° C. are not exceeded), it is possible to produce organic solar cells as components both flexibly and over a large area on inexpensive substrates, eg metal foil, plastic foil or synthetic fabric. This opens new Fields of application that remain closed to conventional solar cells. Due to the almost unlimited number of different organic compounds, the materials can be tailored to their specific task.

A realization possibility of an organic solar cell already proposed in the literature consists in a pin diode [Martin Pfeiffer, Controlled doping of organic vacuum deposited dye layers: basics and applications ", PhD thesis TU Dresden, 1999.] with the following layer structure:

0. carrier, substrate,

1. basic contact, mostly transparent,

2nd p-layer (s),

3rd i-layer (s)

4th n-layer (s),

5. Deck contact.

Here, n or p denotes an n- or p-type doping, which leads to an increase in the density of free electrons or holes in the thermal equilibrium state. In this sense, such layers are primarily to be understood as transport layers. In contrast, the term i-layer designates an undoped layer (intrinsic layer). One or more i-layer (s) may in this case consist of layers of a material as well as a mixture of two materials (so-called interpenetrating networks). in the

Unlike inorganic solar cells, however, the pairs of charge carriers in organic semiconductors are not free after absorption, but because of the less pronounced attenuation of the mutual attraction they form a quasiparticle, a so-called exciton. To harness the energy present in the exciton as electrical energy make this exciton must be separated into free charge carriers. Since organic solar cells do not have sufficiently high fields to separate the excitons, the exciton separation at photoactive interfaces is completed. The photoactive interface can be used as an organic donor-acceptor interface [CW. Tang, Appl. Phys. Lett. 48 (1986) 183] or an interface to an inorganic semiconductor [B. O'Regan, M. Grätzel, Nature 1991, 353, 737])]. The excitons pass through diffusion to such an active interface, where electrons and holes are separated. This can lie between the p (n) layer and the i-layer or between two i-layers. In the built-in electric field of the solar cell, the electrons are now transported to the n-area and the holes to the p-area. Preferably, the transport layers are transparent or largely transparent materials with a wide band gap (wide-gap). As wide-gap materials here materials are referred to, the absorption maximum in the wavelength range <450 nm, preferably at <400 nm.

Since excitons are always generated by the light and no free charge carriers, the low-recombination diffusion of excitons to the active interface plays a critical role in organic solar cells. In order to make a contribution to the photocurrent, therefore, in a good organic solar cell, the exciton diffusion length must significantly exceed the typical penetration depth of the light, so that the greater part of the light can be used. Structurally and with regard to chemical purity, perfect organic crystals or thin films definitely fulfill this criterion. For large area applications, however, the use of monocrystalline organic materials is not possible and the production of multiple layers with sufficient structural perfection is still very difficult. If the i-layer is a mixed layer, the task of absorbing light either takes on only one of the components or both. The advantage of mixed layers is that the generated excitons only travel a very short distance until they reach a domain boundary where they are separated. The removal of the electrons or holes is carried out separately in the respective materials. Since in the mixed layer the materials are in contact with each other everywhere, it is crucial in this concept that the separate charges have a long service life on the respective material and that there are closed percolation paths for each type of charge to the respective contact from each location. These closed percolation paths are usually realized by a certain phase separation in the mixed layer, ie the two components are not completely mixed, but there are (preferably crystalline) nanoparticles of one material in the mixed layer. This partial segregation is referred to as phase separation.

The thus generated free charge carriers can now be transported to the contacts. By connecting the contacts via a consumer, the electrical energy can be used. Of particular importance is that excitons generated in the bulk of the organic material can diffuse to this photoactive interface.

The low-recombination diffusion of excitons to the active interface therefore plays a critical role in organic solar cells. In order to make a contribution to the photocurrent, therefore, in a good organic solar cell, the exciton diffusion length must at least be of the order of magnitude of the typical penetration depth of the light, so that the greater part of the light can be used. The already mentioned possible high absorption coefficients are particularly advantageous for the production especially thin organic solar cells.

However, it is also important to structurally and with respect to their chemical purity produce the most perfect organic crystals or well-ordered thin films, since these have the highest mobilities for both excitons and charge carriers. Larger organic crystals, however, are unsuitable for large-scale applications, since they are difficult to produce on the one hand and mechanically unstable on the other hand. The production of organic thin films with defined proximity of the molecules is therefore an urgent task in the development of organic solar cells.

In this case, this Nahordnung the molecules serves both the low-loss transport of excitons and after their separation into free charge carriers the transport of electrons or holes. A high mobility for charge carriers in these organic absorber layers is therefore another prerequisite for their usability. Particularly advantageous is the case in which one of the components in an organic mixed layer of two different organic components is preferably electronically conductive and the other component is preferably conductive holes.

Instead of increasing the exciton diffusion length, one can also reduce the mean distance to the nearest interface. This can be seen by using very thin absorber layers (with typical layer thicknesses around 10 nm). However, only a partial extinction of the incident light is achieved, which is a major reason for the previously inadequate efficiency of organic solar cells.

WO 00/33396 discloses the formation of a so-called interpenetrating network of two organic materials. alien in the absorber layer: A layer contains a colloidally dissolved substance which is distributed in such a way that two networks form in the bulk material, each having closed charge carrier paths, so that each type of charge carrier (holes and electrons) lies on closed conduction paths of each material with very little loss to the external contacts (percolation mechanism). The task of light absorption takes over in such a network either only one of the components or both. The advantage of this mixed layer is that the generated excitons only have to travel a very short distance until they reach a domain boundary where they are separated. The removal of the electrons or holes is carried out separately. Since the materials in the mixed layer are in contact with each other everywhere, it is crucial in this concept that the separate charges have a long service life on the respective material and that closed percolation paths are present for the respective contact from each location for both types of charge carriers. With this approach, it was possible to use polymeric solar cells

Efficiencies of 2.5% can be achieved [C. J. Brabec et al. , Advanced Functional Materials 11 (2001) 15].

Further known approaches for realizing or improving the properties of organic solar cells are listed below:

One contact metal has a large and the other a small work function, so that a Schottky barrier is formed with the organic layer [US 4127738].

The active layer consists of an organic semiconductor in a gel or binder [US 03844843, US 03900945, US 04175981 and US 04175982].

Production of a Transport Layer Containing Small Particles (Size 0.01 - 50 μm), which Contains the Carrier take over transport [US 5965063].

A layer contains two or more kinds of organic pigments having different spectral characteristics [JP 04024970].

A layer contains a pigment which generates the charge carriers, and additionally a material which removes the charge carriers [JP 07142751].

Polymer-based solar cells containing carbon particles as electron acceptors [US05986206].

Doping of o.g. Mixed systems for improving the transport properties in multilayer solar cells [DE 102 09 789 Al].

Arrangement of individual solar cells on top of each other (tandem cell) [US 04461922, US 06198091 and US 06198092].

Tandem cells can be further improved by using p-i-n structures with doped transport layers of large band gap [DE 10 2004 014046 A1].

Despite the advantages of interpenetrating networks described above, a critical issue is that there must be closed transport paths for both electrons and holes to their respective contacts in the mixed layer. In addition, since the individual materials each fill only a part of the mixed layer, the transport properties for the respective types of charge carriers (electrons and holes) deteriorate significantly compared to the pure layers.

For polymeric materials, mixed-layer systems have already been found which approximate the interpenetrating networks mentioned. Ma, Heeger and co-workers (in: Advanced Functional Materials 15 (2005) 1617-1622) report on polymeric solar cells with an active layer P3HT: PCBM, in which the active layer is modified by a thermal treatment to form an interpenetrating network in the polymer, which leads to solar cells with 5% efficiency. P3HT stands for poly (3-hexyl-thiophene), a polymer from the series

Poly (3-alkylthiophene) (P3AT). The evidence of network formation was obtained in this work by X-ray diffraction and transmission electron microscopy. Also using the P3HT: PCBM polymer blend, the group of Yang Yang (Nature Materials 4 (2005) 864) showed that even through the choice of suitable growth rates, formation of preferred molecular orders can be made which allow solar cell efficiencies of up to 3.6%. The successfully used polymer P3HT is a poly-thiophene with a hexyl chain attached to the 3rd carbon atom. That is, a six C-atom side chain is used.

The formation of ordered molecular structures is therefore of central interest for organic solar cells. The question position is similar to that in organic field effect transistors (OFETs). However, the difference between solar cells and OFETs is as follows: OFETs should have a preferred charge carrier transport parallel to the substrate. Solar cells, on the other hand, are intended to deliver their charge carriers perpendicular to the substrate as quickly as possible and with little loss to the outer electrodes, which are generally flat, and in a frequently used arrangement charge transport layers are incorporated between the absorbent layer (s) and the electrodes. From this it can be deduced that the molecular structures in solar cells should be different from those in OFETs.

Regarding the general question of order formation - without reference to organic solar cells - the influence of the length of the side groups and the regio- larity of their arrangement in polymers and oligomers was already investigated. looks for:

Several papers consistently report side-group-induced self-assembly when the length of the aliphatic side groups in polymers of the class

Poly-3-Alkyl-Thiophene (P3ATs) groß genug ist.

Poly-3-alkyl-thiophene (P3ATs) is large enough.

For P3ATs with large side chain lengths of (CH2) _n with n = 10 or n = 12, McCullough et al. [Journal of the American Chemical Society 115 (1993) 4910] of marked self-assembly. Sirringhaus [Applied Physics Letters 77 (2000) 406] reports self-assembly of a conductive polythiophene with octyl side groups to improve organic field effect transistors (OFETs).

With few exceptions, side chains of at least six carbon atoms in series are used in the literature. The reason given for this is better self-organization when using long side chains. Another factor is the solubility of the monomers in common solvents, which is better for longer side chains. For P3HT with its hexyl side chains, it was found by Babel and Jenekhe [Synthetic Metals 148 (2005) 169] that this poly (3-alkylthiophene) derivative represents the optimum in terms of field-effect carrier mobility due to its self-organization. Even when used in polymeric solar cells, P3HT has been the most efficient polymer to date when blended with the fullerene derivative PCBM.

There are also literature reports on polymers with shorter side chains, mostly butyl chains are used. In terms of molecular orientation, for example, poly (3-butylthiophene (P3BT) is clearly inferior to P3HT. For example, Babel and Jenekhe [Synthetic Metals 148 (2005) 169] investigated the charge carrier mobility of poly (3-butyl-thiophene), which, however, revealed significantly poorer charge carrier mobilities than the hexyl analogue. Guanghao Lu et al. [Macromolecules 41 (2008) 2062] report in detail on the morphology of poly (3-butyl-thiophene). This initially grows amorphous upon deposition from solution, but can be converted into a crystalline phase with the aid of a suitable solvent. However, it shows a strong needle-shaped crystal growth, which precludes the use in components.

Such non-conjugated side chains with four non-H atoms in linear sequence have already been tested in oligomers for solar cell use. Schulze et al. [Adv.

Mater. 18 (2006) 2872] report oligomer solar cells with> 3% efficiency when using a butyl-substituted oligomer. However, order effects could not be found in that work. Instead, for example, the optical absorption and photoluminescence spectra showed largely structureless spectra typical of amorphous substances.

However, side chains with three non-H atoms in the main axis, in particular propyl side groups, have hitherto scarcely been used for reasons already mentioned of poor handling (because of their low solubility) and the associated difficult production of components. Organic solar cells with such side chains - be it solar cells made of polymers or small molecules - find no literature at all.

A similar situation is found for side chains with two non-H atoms in series: For polymers, the solubility which can be achieved in particular is very low, so that such side chains in polymers are extremely rare be used.

Another aspect is the substitution pattern according to which the side chains are attached to the monomer. Consistent studies by various groups show that polymers in which each ring of the backbone carries a side group show better phase separation to PCBM than those that also contain side chain rings. For example, Koppe [Advanced Functional Materials 17 (2007) 1371] reports a comparison of P3HT: PCBM with C6TT-PCBM, in which the polymers differ only in that C6TT is a poly-thiophene with hexyl side groups, in which every third Thiophene is unsubstituted, whereas P3HT has a hexyl side group on each thiophene. In C6TT, sufficient phase separation to PCBM is no longer achieved, which leads to significantly poorer solar cell properties than with P3HT: PCBM. This is another indication that the molecular neighborhood in the active layer plays a crucial role in the efficiency of an organic solar cell.

If one looks at the literature on polymeric solar cells, it is striking that as a rule side chains having six to twelve atoms are used in series, with preference being given to using even-numbered n-alkanes. The frequent use of long chain alkanes as side chains, apart from the good solubility of the corresponding monomers, is based on the widespread belief that, to form a molecular short order, a side chain length of at least six atoms in series, e.g. Hexyl, required.

The invention is thus based on the object of specifying a photoactive component which has improved efficiency.

The object is achieved by an organic photoactive component according to the main claim. advantageous Embodiments are specified in the dependent claims.

According to the invention, when using oligomers instead of polymers, a preferred molecular short-range order can also be achieved with shorter side chains than is usual with polymers. The advantage here is that the

Using shorter side chains may lead to more dense pi-electron systems, which improves the charge transport in these organic materials, which usually takes place by hopping processes.

Particularly advantageous is an arrangement of molecules on a substrate (electrode or other organic layer / layers), as outlined in Fig. Ib. In this case, charge transport perpendicular to the substrate plane is preferred in that the pi-electron systems of adjacent molecules overlap and in that the pi-electron systems are parallel to the substrate, which allows preferential charge transport perpendicular to the substrate.

Oligomers in the context of the invention are substances which are formed from at least one organic material which has a precisely defined molecular structure

Number, but at least two and typically no more than twenty designated as monomers repeating units of at least four atoms from the group C, N, S, Si, Se, and P, wherein at least two of these repeating units are identical. The monomers are preferably pronounced as cyclic compounds with delocalized pi-electron system.

A monomer in the context of the present invention is an organic molecular substructure with a common pi-electron system formed from at least four atoms from the group C, N, S, Si, Se, P.

Another aspect is the light absorption. This becomes maximum when the longitudinal axes of the preferred as a rod-shaped pronounced oligomer molecules are orthogonal to the direction of light incidence. If one assumes perpendicular incidence of light on the substrate, it turns out that it is particularly advantageous for high light absorption when the molecules as shown in Fig. Ia) and Fig. Ib) are on the substrate, whereas standing molecules, as in Fig. Ic) outlined, absorb less light.

It follows that a molecular arrangement as outlined in FIG. 1 b is particularly advantageous for organic light-absorbing components, in particular solar cells.

To achieve high efficiency, oligomeric solar cells are preferably constructed of absorber material employing short side chain oligomers with n = 3 non-H atoms in series, thereby providing preferential orientation of the oligomers to each other, which provides good optical performance Absorption while allowing good charge transfer between adjacent oligomers. The oligomer is characterized by at least two, but preferably four to six non-conjugated side chains wherein the backbone of at least two of these side chains comprises exactly three atoms from the group consisting of C, Si, O, S, Se, N, P in linear sequence , Another essential aspect of this invention is that the molecular proximity of the oligomers produces a nanocrystalline structure which is designed so that preferential electrical charge transport is perpendicular to the substrate, resulting in higher device efficiency due to lower contact resistances. In this respect, a molecular arrangement according to FIG. Ib) is particularly advantageous.

In a further embodiment of the invention, at least one of the monomers is a heterocycle.

mit X = {0, S, Se, CR3R4, N-R3), wobei Rl, R2 , R3 und R4 ausgewählt ist aus der Gruppe bestehend aus H oder einer nichtkonjugierten linearen Kette von Atomen, wobei das Grundgerüst dieser nichtkonjugierten linearen Kette genau drei Atome aus der Gruppe C, Si, O, S, Se, N, P in linearer Folge umfasst und gleichzeitig mindestens eine der Gruppen Rl, R2, R3 oder R4 nicht H ist.In a further embodiment of the invention, at least one of the monomers has the form

where X = {0, S, Se, CR3R4, N-R3), wherein R1, R2, R3 and R4 are selected from the group consisting of H or a non-conjugated linear chain of atoms, the backbone of this non-conjugated linear chain being exactly three At least one of the groups R 1, R 2, R 3 or R 4 is not H and at least one of the groups C, Si, O, S, Se, N, P comprises in a linear sequence.

In a further embodiment of the invention, the monomer is extended by at least one and at most eight further fused cycles.

In a further embodiment of the invention, the monomer has one of the following basic structures, wherein X and Y are independently selected from a group consisting of O, S, Se, CR3R4, N-R3:

In a further embodiment of the invention, the monomers in any selected order form an oligomer, wherein the oligomer carries a total of at least two side chains.

In a further embodiment of the invention, the monomers in the oligomer have, in addition to the direct bond via C-C, a further bridge C-S-C, C-CR3R4-C, C-NR3-C or C-O-C and have the following basic structure

, wobei Z aus der Gruppe bestehend aus S, CR3R4 , NR3 , oder O ausgewählt ist.

wherein Z is selected from the group consisting of S, CR3R4, NR3, or O.

In a further embodiment of the invention, the monomers in the oligomer have a further bridging via a benzene ring and one of the following basic structures

In a further embodiment of the invention, the oligomer carries one or more further side chains which, however, each comprise only n <3 atoms from the group consisting of C, Si, O, S, Se, N, P in linear sequence.

In another embodiment of the invention, the oligomer is an acceptor-donor-acceptor or donor-acceptor-donor molecule, as disclosed in WO 002006092134 A1.

In a further embodiment of the invention, the oligomer is a molecule which has four or more carries six side chains and has mirror and / or point symmetry.

In a further embodiment of the invention, the oligomer is a molecule comprising a monorange sequence of 5 consecutive conjugated monomers, wherein the 1st, 2nd, 4th and 5th monomer each carry a non-conjugated side chain ,

In a further embodiment of the invention, the oligomer is a molecule which comprises a monomer sequence of 5 consecutive conjugated monomers, and the second and fourth monomers each have one side chain and the first and fifth monomers each have two Carries side chains.

In a further embodiment of the invention, the oligomer is a molecule comprising a monomer sequence of 5 consecutive conjugated monomers, wherein in each case the 1st and 5th or the 2nd and 4th monomer are each two non-conjugated monomers Carry side chains.

In a further embodiment of the invention, the oligomer is a molecule which comprises a monomer sequence of 6 consecutive conjugated monomers, where in each case the 1st, 2nd, 5th and 6th monomer or the 1st, 3rd ., 4th and 6th monomer each carries a non-conjugated side chain.

In a further embodiment of the invention, the oligomer is a molecule comprising a monomer sequence of 6 consecutive conjugated monomers, wherein the 1st and 6th monomers, or the 2nd and 5th monomers each have two non-conjugated side chains wear.

In a further embodiment of the invention, the oligomer is a molecule which is at least includes two n-propyl groups as a side chain.

In a further embodiment of the invention, the oligomer is a molecule with the following monomer sequence:

In a further embodiment of the invention, the oligomer is a molecule which is referred to as

acceptor-like end group DCV with the structure

, oder eine der folgenden akzeptorartigen Monomere mit oder ohne zusätzliche periphere Substituenten enthält: Cyano- Bicyano oder Tricyano-Vinylen, verbrückte Dithiopheneinheit mit elektronenziehender Brücke, Benzothiadiazol, Oxadiazol, Triazol, Benzimidazol, Quinoline, Quinoxaline, Pyrazoline, Naphthalen-Dicarbonsäure-Anhydride, Naphthalene- Dicarbonsäure-Imide, Naphthalene-Dicarbonsäure-Imidazole, halogenierte Homo- und Heterozyklen, Di- oder Triarylboryl, Dioxaborin-Derivate, chinoiden Strukturen, Aryle mit Keton- oder Dicyanomethan-Substituenten.MeDCV with the structure

or one of the following acceptor-like monomers with or without additional peripheral substituents: cyano-bicyano or tricyano-vinylene, bridged dithiophene unit with electron-withdrawing bridge, benzothiadiazole, oxadiazole, Triazole, benzimidazole, quinolines, quinoxalines, pyrazolines, naphthalene-dicarboxylic acid anhydrides, naphthalenedicarboxylic acid imides, naphthalenedicarboxylic acid imidazoles, halogenated homo- and heterocycles, di- or triarylboryl, dioxaborine derivatives, quinoid structures, aryls with ketone or dicyanomethane substituents.

The invention will be explained in more detail below with reference to some embodiments and figures. The associated figures show in

1 is a schematic representation of the orientation of the molecule longitudinal axis to the substrate, in

Fig. 2 is an illustration of the current-voltage characteristics in various absorber materials and in

3 shows a representation of the absorption spectra of the various absorber materials.

Embodiment 1

Based on a series of substances, the present invention will be demonstrated. For this purpose, organic solar cells of the following layer sequence were produced:

Support material glass / ground electrode indium tin oxide (ITO) / hole transport layer (HTL) / undoped HTL / absorber 1 oligomer DCV5T-X4 with variable side chain lengths x = ethyl (Et), propyl (Pr), or Butyl (Bu) / absorber 2 fullerene C60 / electron transport layer (ETL) / cover electrode aluminum. The molecular structure of the oligomeric material DCV5T-X4 is as follows:

The current density-voltage characteristics of these components are shown in Fig. 2.

It is surprising that of these oligomers just the one with propyl side chain, ie that with three non-H atoms in the side chain, shows the best component parameters. Alone, only one atom of butyl in the side chain shows significantly poorer intermolecular charge carrier transport. This is all the more surprising since side chains with at least n = 6 atoms in linear sequence, often even more, are used in polymeric solar cells. For ethyl, on the other hand, an equally good fill factor is observed as for propyl, but significantly lower currents and voltages.

The cause of the lower stress in ethyl is a more red-absorbing absorption of ethyl based on lower propyl formation. This can be seen from the absorption spectra of the three absorber materials discussed in FIG.

If one compares these results with the literature data known from polymeric solar cells, in which at least six atoms are used in the side chains (eg in P3HT as discussed above), it is surprising that for oligomers already in 4 atoms in series efficiency losses in shape However, in polymers side chains of at least six, often up to twelve atoms in length are the rule.

The use of short side chain oligomers is generally advantageous for solar cells because they meet various organic solar cell requirements: First, both the monomers having such side chains and the oligomers formed therefrom are up to a typical oligomer length of about 7 or 8 repeat units (Mono - Meren) soluble in common solvents and thus manageable. On the other hand, as a result of the well-defined and short side chains, the formation of a molecular order of proximity is possible. This allows the desired formation of nanocrystalline phases, which are a prerequisite for the formation of interpenetrating networks. Thirdly, intermolecular charge transport across the longitudinal axis of the rod-shaped oligomers is possible as a result of the short-chain side chains by means of tunneling processes. Fourth, the molecules are small enough that they can be vacuum deposited by thermal sublimation. Alternatively, their deposition from carrier gases or from solution is possible, which is e.g. can be done by printing, spraying, pouring or spin coating.

In experiments it has been shown that triatomic side chains are particularly suitable for use in organic mixed layers. This is particularly surprising insofar as propyl is very unusual as a side chain in the extensive literature on the field of organic electronics and is extremely rarely mentioned as a side chain in oligothiophenes. In solar cells, none of these substances was used.

Oligomers consisting of monomers with different lateral chains are composed, are a further advantageous possibility for structure formation. It may be particularly advantageous to use such different side chains, which show mutually preferred interactions. In this way, a preferred proximity of the molecules can be achieved, which can be used for a low-loss charge transport of the oligomer layer.

Embodiment 2

In a further embodiment of the invention triatomic side chains are attached to oligomers of five or six heterocycles. The molecules are selected so that they follow the structure described in WO 2006-092134 Al: At least one end, better at both ends of the oligomer chain each an acceptor group (in the present example, a Dicyanovinyl unit) attached, the electronic Properties of the substance. This results in exemplary, but by far not exclusively, substances of the following type:

1) Oligothiophenes with propyl side chains:

b) kondensierte Oligomere , z . B ,

b) condensed oligomers, e.g. B,

c) oligothiophenes having side chains of 3 non-H atoms in linear sequence other than alkane chains, e.g.

d) Oligothiophene mit verschiedenen Seitenketten, z.B.

d) Oligothiophene with different side chains, eg

e) Oligomere, die keine Oligothiophene sind, z.B.

f) Oligomere, die verschiedene Monomere beinhalten, z.B.

e) Oligomers, which are not oligothiophenes, eg

f) oligomers containing different monomers, eg

Claims

Light-absorbing organic component patent claims 1. Organic, photoactive component, in particular a solar cell, with a pi-conjugated oligomer consisting of two to twenty, but preferably three to six, monomers as a photoactive, light-absorbing material, characterized in that the oligomer is composed of at least two, but preferably four to six non-conjugated side chains, the basic structure of at least two of these side chains comprising exactly three atoms from the group consisting of C, Si, O, S, Se, N, P in a linear sequence. 2. Component according to claim 1, characterized in that at least one of the monomers is a heterocycle. 3. Component according to claims 1 and 2, characterized in that at least one of the monomers has the form

and R4 is selected from H or a non-conjugated linear chain of atoms, the base framework of this non-conjugated linear chain comprises exactly three atoms from the group C, Si, O, S, Se, N, P in a linear sequence, and at the same time at least one of the groups Rl, R2, R3 or R4 is not H. 4. Component according to one of the preceding claims, characterized in that the monomer is expanded by at least one and a maximum of eight further condensed cycles. 5. Component according to claim 4, characterized in that the monomer has one of the following basic structures, where X and Y are independently selected from a group consisting of O, S, Se, CR3R4, N-R3:

6. Component according to one of the preceding claims, characterized in that the monomers form an oligomer in any selected order, the oligomer carrying a total of at least two side chains. 7. Component according to one of the preceding claims, characterized in that the monomers in the oligomer have, in addition to the direct bond via C-C, a further bridge C-S-C, C-CR3R4-C, C-NR3-C or C-O-C and have the following basic structure

, where Z is selected from the group consisting of S, CR3R4, NR3, or 0. 8. Component according to one of the preceding claims, characterized in that the monomers in the oligomer have a further bridge via a benzene ring and one of the following basic structures

9. Component according to one of the preceding claims, characterized in that the oligomer carries one or more further side chains, which, however, only comprise n <3 atoms from the group consisting of C, Si, O, S, Se, N, P in a linear sequence. 10. Component according to one of the preceding claims, characterized in that the oligomer is an acceptor-donor-acceptor or donor-acceptor-donor molecule. 11. Component according to one of the preceding claims, characterized in that the oligomer is a molecule which carries four or six side chains and has mirror and/or point symmetry. 12. Component according to one of the preceding claims, characterized in that the oligomer is a molecule which comprises a monomer sequence of 5 consecutive conjugated monomers, the 1st, 2nd, 4th and 5th monomer each being one carries a non-conjugated side chain. 13. Component according to one of claims 1 to 11, characterized in that the oligomer is a molecule which comprises a monomer sequence of 5 successive conjugated monomers, the 2nd and 4th monomer each having a side chain and the 1st and 5th monomers each have two side chains. 14. Component according to one of claims 1 to 11, characterized in that the oligomer is a molecule which comprises a monomer sequence of 5 successive conjugated monomers, the 1st and 5th or the 2nd and 4. Monomer each carries two non-conjugated side chains. 15. Component according to one of claims 1 to 11, characterized in that the oligomer is a molecule which comprises a monomer sequence of 6 successive conjugated monomers, with the 1st, 2nd, 5th and 6th in each case. Monomer or the 1st, 3rd, 4th and 6th monomer each carries a non-conjugated side chain. 16. Component according to one of claims 1 to 11, characterized in that the oligomer is a molecule which comprises a monomer sequence of 6 successive conjugated monomers, the 1st and 6th monomer or the 2nd and 5th .Monomers each carry two non-conjugated side chains. 17. Component according to one of the preceding claims, characterized in that the oligomer is a molecule which comprises at least two n-propyl groups as a side chain. 18. Component according to one of the preceding claims, characterized in that the oligomer is a molecule with the following monomer sequence:

19. Component according to one of the preceding claims, characterized in that the oligomer is a molecule which is an acceptor-like molecule End group DCV with the structure MeDCV with the structure

, or an acceptor-like one Monomer with or without additional peripheral substituents selected from the group consisting of cyano-bicyano or tricyano-vinylene, bridged dithiophene unit with electron-withdrawing bridge, benzothiadiazole, oxadiazole, triazole, benzimidazole, quinoline, quinoxaline, pyrazoline, naphthalene Dicarboxylic anhydrides, naphthalene-dicarboxylic imides, naphthalene-dicarboxylic imidazoles, halogenated homo- and heterocycles, di- or triarylboryl, dioxaborine derivatives, quinoid structures, arylene with ketone or dicyanomethane substituents.