Organic photoactive component

Organic photoactive component

The present invention relates to an organic photoactive component, in particular an organic photovoltaic cell, comprising a contact and a countercontact, as well as an organic zone that is electrically connected with the contact and with the countercontact, being formed in the area organic a photoactive zone with a photoactive heterounion between an electron-conducting organic material and a hollow-conducting organic material.

Background of the invention

Research and progress in the field of organic photoactive components, which in a known embodiment are formed by an organic solar cell or organic photovoltaic cell, have increased considerably over the past ten years. The maximum efficacy published to date is 5.7% (see Jiangeng Xue et al., Appl. Phys. Lett. 85 (2004) 5757). In this way, it has not yet been possible until now to achieve for organic solar cells the typical efficiencies between 10 and 20%, such as are known for inorganic solar cells. However, using organic solar cells, it should be possible to achieve results similar to those of inorganic solar cells based on inorganic materials.

The advantages of organic solar cells over inorganic solar cells lie in particular in the lower costs. The organic semiconductor materials used if prepared in large quantities are available at favorable costs. Another advantage is the optical absorption coefficients, some of which are very high and reach up to 2x105 cm -1, which offers the possibility of preparing very thin, but efficient solar cells, using little material and energy. Since high temperatures are not required in the preparation process, that is, substrate temperatures of only about 110 ° C at most, it is possible to prepare flexible components of large surface area on plastic films or plastic fabrics. This opens up new fields of application, which are closed to conventional solar cells. Due to the almost unlimited number of different organic compounds, the materials can be tailored for their respective task.

In an organic photoactive component, light energy is converted into electrical energy. Unlike inorganic solar cells, in the organic semiconductor material of the organic photoactive component, the charge carrier pairs (electron-hollow pair) are not freely present after light absorption, but form a quasiparticle, a so-called exciton, due to the less pronounced weakening of mutual attraction, that is, a pair of bound electron-hole. For the available energy to be usable as electrical energy, the exciton formed in this way must be separated into free charge carriers, that is, in an electron and a hole.

Since in the organic solar cells they are not available in fields high enough for the separation of the excitons, the separation of the excitons is carried out in photoactive interfaces. The photoactive interface can be formed by an organic donor-acceptor interface (see CW Tang, Appl. Phys. Lett., 48 (2), 183-185 (1986) or as an interface with an inorganic semiconductor (see B. O 'Regan et al., Nature 1991, 353, 73). The free load carriers can be transported after their separation to the contacts. Electric power can be harnessed by connecting contacts through consumers.

An organic material for the purposes of the present application is called a hollow conductor if in the material the load carriers formed as a result of light absorption and separation of the charges in a heterounion ("photogenerated load carriers") are transported in hollow shape Similarly, an organic material is called an electron conductor if the photogenerated charge carriers in the material are transported in the form of electrons. An interface zone between the electron conducting material and the hole conducting material is called heterojunction.

A heterounion between the electron conductive material and the hollow conductive material is called photoactive heterounion if the excitation states formed in the electron conductive / conductive material of light absorption, in which the charge carriers are bound and the which are also called excitons, are separated into the individual charge carriers in the heterojunction zone, that is, electrons and holes, which in turn are then transported by the electron conducting material / conductive material of holes to the contacts, where electrical energy can be taken.

A heterojunction between the electron conductive material and the hollow conductive material is called a flat junction if the interface between the electron conductive material and the hollow conductive material is formed by a substantially continuous zone between the two material zones, i.e. , a zone constituted by the electron conducting material and a zone constituted by the conductive material of holes (see CW Tang, Appl. Phys. Lett., 48 (2), 183-185 (1986) or N. Karl et al., Mol. Cryst Liq. Cryst., 252, 243-258 (1994)).

A heterojunction between the electron conducting material and the conductive material of holes is a volume heterojunction if the electron conducting material and the conductive material of holes are mixed at least in part, so that the interface between the electron conducting material and the hollow conductive material comprises a large number of interface surface sections that are distributed by the volume of the material mixture (see, for example, CJ Brabec et al., Adv. Funct. Mater., 11 (1), 15 (2001)).

Ideally, the materials of photoactive layers in the components have a high absorption coefficient in a range of wavelengths as wide as possible adapted to the solar spectrum. The exciton generated in the semiconductor material by absorption should be able to diffuse to the photoactive heterounion without large losses of energy, any stokes movement that appears must be minimal. The diffusion lengths of long excitons allow to maximize the thickness of the organic layers in which the absorbed light contributes to the photocurrent, thereby improving the efficiency of the organic photoactive component even further.

Further, a higher occupied energy level (HOMO) and a lower unoccupied energy level (LUMO) of the organic acceptor material (electron conducting material) and the organic donor material (hollow conductor material) should preferably be selected in such a way that on the one hand an effective separation of the excitons takes place in electrons in the acceptor material and in holes in the donor material and on the other hand the free energy of the electron and hole system generated is the as much as possible The latter leads to maximization of the open circuit phototension of the component. Load carriers should be spatially separated from each other quickly. An efficient electron transport in the acceptor material and an effective hole transport in the donor material guarantee small losses and give rise to a good filling factor of the current / voltage characteristic of the organic photoactive component.

Organic solar cells are known in the state of the art in various designs:

<dl><dt>-</dt><dd>A contact metal has a great electronic affinity and the other a small contact metal, which forms a Schottky barrier with the organic layer (see US 4,127,738). </dd></dl>

<dl><dt>-</dt><dd>The photoactive layer consists of an organic semiconductor in a gel or binder (US 3,844,843, US 3,900,945, US 4,175,981 and US 4,175,982). </dd></dl>

<dl><dt>-</dt><dd>A transport layer of charge carriers is formed containing small particles with a size between 0.01 and 50 µm, which carry the transport of the load carriers (see US 5,965,063). </dd></dl>

<dl><dt>-</dt><dd>A layer of the solar cell contains two or more types of organic pigments, which have different spectral characteristics (see JP 04024970). </dd></dl>

<dl><dt>-</dt><dd>A layer of the solar cell contains a pigment that produces charge carriers and additionally a material that carries the charge carriers out (see, JP 07142751). </dd></dl>

<dl><dt>-</dt><dd>Polymer-based solar cells were prepared, containing carbon particles as electron acceptors (see, US 5,986,206). </dd></dl>

<dl><dt>-</dt><dd>A mixed system doping was planned to improve transport properties in multilayer solar cells (see, DE 102 09 789). </dd></dl>

<dl><dt>-</dt><dd>Arrangements of individual solar cells were formed one above the other (tandem cell) (US </dd></dl>

4,461,922; US 6,198,091 and US 6,198,092). Tandem cells can be further improved using pi structures

n with doped transport layers of large interval between bands (see DE 103 13 232).

US Patent No. 5,093,698, discloses the doping of organic materials. Adding a doping substance, that is, a substance with high electronic affinity for doping po of a substance with low ionization energy for doping, increases the concentration of equilibrium charge carriers in the doped layer and conductivity. Given the state of the art of US Patent No. 5,093,698, the doped layers are used as injection layers at the interface with the contacts in the photoluminescent components.

In US Patent No. 5,849,403, thin organic layers are described consisting of a material with donor and acceptor molecules that are arranged relative to each other, forming complex crystalline structures. There are two types of complexes: neutral complexes, that is, donor and acceptor molecules without charge transfer, as well as ionic complexes in which a partial charge transfer takes place. In both cases, the components of the complexes are free of covalent bonds.

In US 2004/0147701 A1, chemical compounds with a group of electron donors, a group of electron acceptors as well as a conjugated bridge between the group of electron donors and the group of electron acceptors have been described. In one embodiment, the following structure has been formed: acceptor-bridge-donor-bridge-acceptor.

Summary of the invention

The objective of the invention is to create an organic photoactive component, in particular an organic photovoltaic cell of the type mentioned at the beginning with improved performance.

Said objective is achieved by means of the organic photoactive components according to independent claims 1, 2 and 3.

Due to the use of conjugated acceptor-donor-acceptor oligomers (AD-A 'oligomers) and conjugated donor-acceptor-oligomers (DA-D' oligomers), various advantages are obtained over the prior art. , which will be discussed in more detail below.

When the AD-A '/ DA-D' oligomers are used with an extended donor block as a conductor component of holes in a photoactive heterounion, be it a flat heterounion or a volume heterounion, for an electron conducting material, the separation of excitons It produces holes in the heterojunction on the oligomer, which are delocalized within the donor block / donor blocks. Offshoring results in a decrease in electrostatic interaction with the electron found in the electron-conducting material after separation, whereby the two charge carriers can be separated efficiently and even through low electric fields. The relocation of the gaps provides them with high mobility and allows them to be quickly and efficiently unloaded with only small losses due to recombination. This is particularly advantageous in volume heterojunctions, in which both charge carriers coexist in a mixed volume of the conductor conductive component and the electron conductor component and are not in danger of recombining until they have left said volume.

Similarly, the AD-A '/ DA-D' oligomers comprising an extended acceptor block are used as an electron conducting component in a photoactive heterounion for a hole conducting material. The advantages for exciton separation and electron transport result analogously from the delocalisation of electrons over the acceptor block / acceptor blocks.

With the use of the AD-A '/ DA-D' oligomers as an electron conducting and / or conductor conductor component in a flat heterounion, it has surprisingly been found that the oligomers without an extended block of acceptors in combination with a suitable hole conductor can also advantageously be used as an electron conductor, although in this case the electrons formed in the exciton separation are not delocalized on the oligomer. In volume heterojunctions, a use of this type leads to very low efficiencies, due to the low mobility of electrons and as a result to the high losses due to recombination. All the advantages of the proposed class of materials, with the exception of an increased mobility of photogenerated cargo carriers, are fully deployed in flat heterojunctions. The problem of low mobility of charge carriers can be overcome using a flat heterounion, in which there is no volume in which electrons and holes can coexist and, therefore, recombinations can no longer occur, once the excitons are have separated.

Unlike polymeric compounds, oligomers are distinguished by the fact that they comprise a well defined number of monomers (recurring units), which is typically between three and ten. In this way, the oligomers form molecules of a defined number of monomers. Thus, they have a well-defined molecular weight, typically less than 1200 g / mol and are free of possible reactive groups, not defined at the end of the molecular chain, such as may be present in the polymers as byproducts of a reaction of polymerization in chain.

Among the technological advantages of oligomers, they also include their evaporability under vacuum, which entails the possibility of purification by gradient sublimation. This results in the possibility for the oligomers applicable by evaporation to prepare almost any complex multilayer system by sequential evaporation of various pure or mixed materials. The mixed layers of controlled composition are prepared by application by simultaneous evaporation of various materials on a substrate from different sources of evaporators, the evaporation rates can be controlled separately, for example by oscillating quartz monitors.

This also allows preparing n-doped py layers and mixed layers of photoactive donor-acceptor in a controlled manner. During this process, the morphology of the mixed layers can be varied within a wide range by selecting the substrate temperature during evaporation. In cold substrates, a homogeneous, substantially amorphous mixture is typically produced, while at higher substrate temperatures a separation of nanophases and possibly a formation of crystalline nanodomins is obtained to a greater extent. Said control through phase separation achieves a size scale between 10 and 100 nm, which is particularly advantageous in volume heterojunctions. For polymers applied by injection of mixed solutions, a too pronounced phase separation is often observed, in particular when one of the components has too low solubility.

Using the AD-A 'oligomers and DA-D' oligomers according to the various aspects of the invention, it has been possible to achieve much higher photovoltaic efficiencies compared to all known solar cells based on conjugated oligomers. Until now, comparable efficiencies have been achieved only with polythiophene and large condensed molecules, such as phthalocyanine or perylene derivatives, which, however, do not have an oligomeric character. The reason for this advance lies in a combination of unique properties of the class of materials used and in their selective use in organic photactive components, thus utilizing the properties of the materials optimally.

In comparison with conventional oligomers, AD-A 'oligomers and DA-D' oligomers are distinguished by their intramolecular donor-acceptor effect, which is already manifested in solution, which results in a substantially displaced optical absorption spectrum towards longer wavelengths. This solves a problem of conventional photovoltaic oligomers, which have a wider range between optical bands than analog polymers.

When thin layers of the AD-A '/ DA-D' oligomers are formed, the absorption spectrum is broadened and moves more towards longer wavelengths, the spectral flap with the solar spectrum being further improved. On the contrary, in thin layers of conventional oligomers, a shift towards shorter wavelengths is often observed (see, for example, the data for quinquethiophene in D. Fichou and C. Ziegler, Chap. 4, p. 227 in: D. Fichou (Ed.) Handbook of Oligo-and Polythiophenes, Wiley-VCH, Weinheim, 1999, or Table 1 in: J. Gierschner et al., J. Chem. Phys. 123, p. 144914 (2005)).

The AD-A '/ DA-D' oligomers have an intense fluorescence shifted only slightly towards the longest wavelengths, relative to the maximum absorption, since the optically allowed transition is also at the same time the lowest energy excitation state , so that little energy is lost by relaxation in the exciton band. Therefore, the ratio of the range between optical bands to the maximum possible phototension is more favorable than for conventional oligomers, in which the formation of so-called H aggregates in thin layers often produces a fluorescence substantially shifted towards the longer wavelengths. long, very inefficient, This can be explained by the high energy losses due to relaxation processes in the exciton band immediately after excitation and / or excimer formation (see J. Gierschner et al., J. Chem. Phys.123, p. 144914 (2005)).

The energies of a lower unoccupied orbital (LUMO) and / or a higher occupied molecular orbital (HOMO) of conventional donor / acceptor oligomers can be optimized energy for requirements in organic photoactive components by incorporating them into AD-A oligomers '/ DA-D'. For example, the incorporation of conventional donor oligomers into the AD-A '/ DA-D' oligomers can lead to a decrease in HOMO and an even more pronounced decrease in LUMO, compared to the corresponding conventional donor oligomer, which simultaneously results in a reduction in the interval between optical bands and an increase in phototension if the AD-A '/ DA-D' oligomer is used as a conductor of holes in a photactive heterojunction with a given electron conductor, for example fullerene C60.

Compared to simple donor-acceptor oligomers (DA oligomer), AD-A '/ DA-D' oligomers have a lower or minimum dipole moment, which decreases dipole disorder in amorphous or polycrystalline solids, for example in thin layers. A dipole disorder should be avoided, since it dramatically reduces the mobility of cargo carriers (see PM Borsenberger et al., J. Chem. Phys., 95 (7), 5327-5331 (1991)).

The AD-A '/ DA-D' oligomers have the additional advantage of comprising at least one extended donor block or an extended acceptor block. With the help of the extended blocks, a desired delocalization of the excitons formed by light absorption can be achieved, whereby the subsequent separation of the load carriers is optimized. On the other hand, alternating DA molecules with a sequence of DADAD monomers… suffer from the problem that the “On-Chain” bandwidth drops, since for example the HOMO wave function focuses on the donor modules and the interaction between the HOMO orbitals that results in a band separation decreases, if they include acceptor components that do not offer any level that can resonate with the donor's HOMO. This decreases the effective length of conjugation, whereby minimal disturbances can already cause a location of charge carriers substantially in a single monomer, which in turn adversely affects the separation of excitons and the transport of charge carriers.

To better understand the invention, the names used in the present application will be explained in greater detail below.

An AD-A 'oligomer conjugated to an extended donor / acceptor block will be referred to herein also as an AD-A'-BCO oligomer ("acceptor-donor-acceptor block cooligomer"). Similarly, an DA-D 'oligomer conjugated to an extended donor / acceptor block will also be referred to as DA-D'-BCO oligomer ("donor-acceptor-donor block cooligomer"). It is understood that at least one extended donor block or two extended acceptor blocks are present in AD-A'-BCO and one extended acceptor block or two extended donor blocks are present in DA-D'-BCO.

For the purposes of the present application, a unit is a group of atoms within a chemical compound comprising at least one monomer. For the purposes of the present application, a monomer is a group of atoms within a chemical compound that comprises at least one subgroup of atoms with a conjugated π electron system and that meets the condition that the group of atoms is not constituted by several units of the same type joined only through a link.

A unit forms an acceptor unit, relative to a donor unit, if a lower unoccupied orbital (LUMO) of the acceptor unit is energetically lower at least 0.2 eV, preferably at least 0, 3 eV, than a lower unoccupied orbital (LUMO) of the donor unit. For a further optimization of the acceptor effect, in an advantageous embodiment it can be provided that a higher occupied orbital (HOMO) of the acceptor unit is energetically lower at least 0.1 eV, preferably at least 0 , 2 eV, than a higher occupied orbital (HOMO) of the donor unit.

Similarly, it is understood that a unit forms a donor unit, relative to an acceptor unit, if a higher occupied orbital (HOMO) of the donor unit is energetically higher at least 0.2 eV, preferably at least 0.3 eV, than a higher occupied orbital (HOMO) of the acceptor unit. For further optimization of the donor effect, in an advantageous embodiment it may be provided that a lower unoccupied orbital (LUMO) of the donor unit is energetically higher at least 0.1 eV, preferably at least in 0.2 eV, than a lower unoccupied orbital (LUMO) of the acceptor unit.

If at least one of the participating units comprises several monomers, a unit forms an acceptor unit with i (i ≥ 1) Ai monomers, relative to a donor unit with j (j ≥ 1) Dj monomers, if in the unit of acceptor, for at least one monomer adjacent to the donor unit, a lower unoccupied orbital (LUMO) is energetically lower at least 0.2 eV, preferably at least 0.3 eV, that a lower unoccupied orbital (LUMO) of an adjacent adjacent monomer in the donor unit, which in the donor unit forms the neighbor of the adjacent monomer in the acceptor unit. In a further preferred development, the aforementioned energy ratios are valid for all monomers of the acceptor unit, relative to all monomers of the donor unit. The previous discussions regarding the additional optimization of the acceptor effect are analogously applicable. It may also be provided that the acceptor unit comprises several monomers and the donor unit only one and vice versa.

If at least one of the participating units comprises several monomers, a unit also forms an acceptor unit with i (i ≥ 1) Ai monomers, relative to a donor unit with j (j ≥ 1) Dj monomers, if satisfied the following condition, which can be tested experimentally in the solid for example by means of electrochemical measurements in solution and / or by a combination of photoelectronic spectroscopy and optical spectroscopy: Attaching the acceptor unit on one or both sides of the donor unit leads to a decrease of an unoccupied lower orbital (LUMO) of the molecule formed in this way by at least 0.2 eV, preferably at least 0.3 eV, relative to a lower unoccupied orbital (LUMO) of the donor unit, while a higher occupied orbital (HOMO) of the molecule thus formed is energetically level, decreases or rises by 0, 1 eV, maximum.

For the purposes of this application, also considered as a unit is a donor unit with i (i ≥ 1) Di monomers, relative to an acceptor unit with j (j ≥ 1) Aj monomers, if in the donor unit, for at least one monomer adjacent to the acceptor unit, a higher occupied orbital (HOMO) is energetically higher at least 0.2 eV, preferably at least 0.3 eV, that a higher occupied orbital (HOMO) of an adjacent adjacent monomer in the acceptor unit, which in the acceptor unit forms the neighbor of the adjacent monomer in the donor unit. In the preferred case, the aforementioned energy ratios are also valid for all monomers of the donor unit, relative to all monomers of the acceptor unit. The above exposures regarding the additional optimization of the donor effect are similarly applicable.

For the purposes of this application, also considered as a unit is a donor unit with i (i ≥ 1) Di monomers, relative to an acceptor unit with j (j ≥ 1) Aj monomers, if the following condition is met, which can be tested experimentally in the solid for example by means of electrochemical measurements in solution and / or by a combination of photoelectronic spectroscopy and optical spectroscopy: attaching the donor unit on one or both sides of the acceptor unit leads to the elevation of a higher occupied orbital (HOMO) of the molecule thus formed in at least 0.2 eV, relative to a higher orbital occupied 0.3 eV (LUMO) of the acceptor unit, while a lower unoccupied orbital (LUMO) of the molecule thus formed is energetically level, rises or decreases by 0.1 eV, at most.

An acceptor unit is an extended acceptor block, if the acceptor unit (i) comprises at least two monomers, preferably at least three monomers and / or if the acceptor unit (ii) comprises at least eight, preferably at least ten atoms with a common π electron system formed by atoms of one or more chemical elements of the following group of elements: C, N, B, P, S, Si and O. The latter can be fulfilled in particular also if the acceptor unit comprises only one monomer. Similarly, an extended donor block based on a donor unit is defined. The extended blocks help in the desired delocalization of the excitons formed by light absorption, whereby the separation of the load carriers is optimized.

In a further preferred development of the invention, an extended acceptor block is distinguished by the fact that the extended acceptor block contains at least one extended acceptor sub-block, which in turn is an extended block in the sense mentioned above and in which the lowest unoccupied orbital (LUMO) of all monomers participating in the acceptor subblock is in an energy range with a width of approximately 0.5 eV, at most, preferably of 0.3 eV, at most, so that a wave function for electrons has large coefficients as uniform as possible in the participating monomers of the extended acceptor subblock. Similarly, it is understood that in a further preferred development of the invention, an extended donor block contains at least one extended donor subblock, which in turn is an extended block in the sense cited above and in which the orbital Highest occupied (HOMO) of all monomers participating in the donor sub-block is in an energy range with a width of approximately 0.5 eV, maximum, preferably 0.3 eV, maximum, so that a wave function for the gaps has large coefficients that are as uniform as possible in the monomers participating in the extended donor subblock.

Preferably, the separation of charges after light absorption occurs in such a way that the type of charge carrier formed on the oligomer (electrons; holes) is delocalized within the extended block, which improves both the separation of charges and the transport of subsequent cargo carriers. Relocation of charge carriers further reduces the local spin density of charged molecules, which generally decreases the reactivity of species in the form of free radicals, increasing their electrochemical stability.

In a further advantageous development of the invention, it is envisioned that in the conjugate acceptor-donor acceptor oligomer (oligomer AD-A '), the acceptor unit (A) and the additional acceptor unit (A') are formed by monomers of the same kind. Such a structure of the oligomers has the advantage that an energetic disorder that appears when a molecule is incorporated in the solid irregularly, for example with the inverted image, is small, whereby relatively high mobilities of the cargo carriers even in the case of disorder. This is analogously valid for conjugate donor-acceptor-donor oligomers (DA-D 'oligomer), in which the donor unit (D) and the additional donor unit (D') are formed by monomers of the same type.

An advantageous embodiment of the invention provides that in the conjugate acceptor-donor-acceptor oligomer (AD-A 'oligomer), the donor unit (D) is a sequence of monomers of type D1D2 ... Dm-1Dm (m&gt; 2) , with a higher occupied orbital (HOMO) of monomers D1 and Dm each being energetically higher by at least 0.2 eV than a higher occupied orbital (HOMO) of the other monomers D2 ... Dm-1. This compensates at least in part for the electron-acceptor effect of the acceptor units on the donor monomers at the edge of the donor block, using monomers that in isolation are particularly rich in electrons, for example ETOD monomers, if the Other monomers are thiophene rings. This counteracts a concentration of the photogenerated holes in the monomers that are not in the immediate vicinity of the acceptor groups and allows the wave function of the holes to be optimally and uniformly distributed throughout the donor block.

Similarly, it can be advantageously provided that in the donor-acceptor conjugate oligomer (DA-D 'oligomer) the acceptor unit (A) is a sequence of monomers of type A1A2 ... Am-1Am (m&gt; 2) , with a lower unoccupied orbital (LUMO) of monomers A1 and Am each being energetically lower by at least 0.2 eV than a lower unoccupied orbital (LUMO) of the other monomers A2… Am-1.

In a further preferred development of the invention, it may be provided that specular or point symmetry is formed in the acceptor-acceptor conjugate oligomer (AD-A 'oligomer). Likewise, in a further advantageous development of the invention, it may be provided that a specular or point symmetry is formed in the donor-acceptor-donor conjugate oligomer (DA-D 'oligomer). The advantage of specular or punctual symmetry is that the static dipole moment is minimized, avoiding a dipole disorder, which reduces the mobility of load carriers. However, high symmetries allow highly ordered layers to form more easily, since certain types of point errors (reflected molecules) are excluded a priori.

In a further advantageous development of the invention, it is envisioned that the contact and / or the countercontact is designed as a transparent or semi-transparent electrode.

A further preferred development of the invention may provide that at least one inorganic layer consisting of one or more inorganic materials is formed between the contact and the countercontact.

An advantageous embodiment of the invention provides that the conjugate acceptor-donor-acceptor oligomer (oligomer AD-A ') and / or the conjugate donor-acceptor-donor oligomer (oligomer DA-D') is formed by an oligomer which has at least one acceptor unit (A; A ') nitrile groups and in which at least one donor unit (D; D') has peripheral hydrogen atoms, such as for example in thiophene derivatives . Here there is an attractive intermolecular interaction between nitrile and hydrogen between the acceptor units of a molecule and the donor unit of adjacent molecules, which helps in an advantageous arrangement of the molecules with each other and with a high displacement in the batteries The formation of nitrilohydrogen bridges of this type can be checked by spectroscopy, since it leads to a characteristic displacement of the vibration modes, in which the hydrogen atom participates.

Advantageously, it can be provided that the contact is an anode and a p-doped organic layer (Mip diode) is arranged between the anode and the photoactive heterounion.

In a further preferred development, it is envisioned that the countercontact is a cathode and that an n-doped organic layer (Min or nip diode) is arranged between the cathode and the photoactive heterounion.

A further advantageous development of the invention can provide that the organic zone has been deposited at least in part by means of thermal deposition under high vacuum or evaporation of organic materials in an inert carrier gas, which transports the evaporated organic materials to a substrate ( "Organic Vapor Phase Deposition").

In an advantageous embodiment of the invention, it is provided that the organic zone has been deposited at least in part from one or more solutions by means of projection, application by scratching and / or printing.

A further preferred development of the invention may provide that the donor unit (D) and / or the additional donor unit (D ') contains at least one of the following donor type monomers with or without additional peripheral substituents: thiophene; thienopyrazine; benzothiadiazola; ethylenedioxothiophene (EDOT) or ethylenedithiothiophene; isotianafteno (ITN); thiophene unit with bridge; 1,3-thiazole; 1,3,4-thiadiazole; thienothiadiazole; thienoselenodiazole; phenyl; naphthyl; anthrazen; tetrazene; pentazeno; vinylene; phenylene vinyl; pyridines; pyrimidines; porphyrin; phthalocyanines; fluorene; carbazola; perylene; pyrene and di-o triarylamine.

A further advantageous development of the invention may provide that the acceptor unit (A) and / or the additional acceptor unit (A ') contains at least one of the following acceptor type monomers with or without additional peripheral substituents: cyano- , dicyano-or tricianovinylene; thiophene unit with an electron-acceptor bridge; benzothiadiazola; oxadiazole; triazole; benzimidazole; quinolines; quinoxalines; pyrazolines; naphthalenedicarboxylic anhydrides; naphthalenedicarboxylic imides, naphthalenedicarboxylic imidazoles, homo- and halogenated heterocycles; di-o triarylboryl; dioxaborine derivatives; Quinoid structures with ketone or dicyanomethane substituents.

In addition, a device may be provided with a stacked arrangement of several organic photoactive components stacked on top of each other, in particular organic photovoltaic cells, in one of the aforementioned embodiments.

Description of preferred exemplary embodiments of the invention

Next, the invention will be illustrated in greater detail by referring to exemplary embodiments in relation to the figures of a drawing, in which:

Fig. 1 shows a schematic representation of an organic photoactive component;

Fig. 2 shows the chemical structure of bis (dicyanovinylene) oligothiophene derivatives: Example of a chemical structure of bis (dicyanovinylene) oligothiophene derivatives, in which n ≥ 1 and R1 - R4 are any radicals, preferably an atom of hydrogen or halogen, nitrile, alkyl, alkoxy or aryl radicals;

Fig. 3 shows an absorption spectrum of DCV3T in solution (circles) and in a deposited layer of a thickness of 30 nm on quartz crystal (quadrangle);

Fig. 4 shows a crystal structure of DCV3T, determined from X-ray diffraction experiments;

Fig. 5 shows a general trace sequence for ADA oligomers conjugated to an extended donor block with specular / point symmetry and dicyanovinylene as an acceptor group;

Fig. 6 shows examples of donor units in conjugated AD-A '/ DA-D' oligomers; zinc (ZnPc) and C60 (triangles).

<dl><dt>Fig. 7 </dt><dd>shows examples of acceptor units based on a dioxaborine group </dd></dl>

<dl><dt>Fig. 8 </dt><dd>shows examples of acceptor units that can be used in conjugated AD-A 'oligomers; </dd></dl>

<dl><dt>Fig. 9 </dt><dd>shows examples of conjugated AD-A 'oligomers in which strong donor units are arranged at both ends of the extended donor block, in which the radicals Y1 and Y2 are oxygen or sulfur atoms and R1-R6 are any radicals, but preferably a hydrogen atom or halogen, nitrile, alkyl, alkoxy or aryl radicals; </dd></dl>

<dl><dt>Fig. 10 </dt><dd>shows examples of DAD oligomers conjugated with an extended acceptor block; </dd></dl>

<dl><dt>Fig. 11 </dt><dd>shows examples of DAD / DA-D 'oligomers conjugated with donor blocks extended at both ends; </dd></dl>

<dl><dt>Fig. 12 </dt><dd>shows examples of AD-A '/ ADA oligomers conjugated with extended acceptor blocks at both ends; </dd></dl>

<dl><dt>Fig. 13 </dt><dd>shows an absorption spectrum in dichloromethane solution and for a deposition layer of DCV-2T-TPy-2T-DCV; </dd></dl>

<dl><dt>Fig. 14 </dt><dd>shows a current / voltage characteristic with illumination for a solar cell with a DCV3T layer with a thickness of 20 nm and a MeO-TPD layer with a thickness of 5 nm; </dd></dl>

<dl><dt>Fig. 15 </dt><dd>shows a current / voltage characteristic with and without illumination for a solar cell with a layer of DCV3T with a thickness of 20 nm and a layer of ZnPc with a thickness of 10 nm; </dd></dl>

<dl><dt>Fig. 16 </dt><dd>shows a current / voltage characteristic with and without illumination for a solar cell with a layer of C60 with a thickness of 20 nm and a layer of DCV5T with a thickness of 15 nm; </dd></dl>

<dl><dt>Fig. 17 </dt><dd>shows an absorption spectrum of DCV5T (a) as well as a fluorescence spectrum of DCV5T (b); </dd></dl>

<dl><dt>Fig. 18 </dt><dd>shows an external quantum yield for the solar cell measured in Fig. 16; </dd></dl>

<dl><dt>Fig. 19 </dt><dd>shows a current / voltage characteristic with illumination for a solar cell based on a photoactive heterojunction between C60 and DCV6T; </dd></dl>

<dl><dt>Fig. 20 </dt><dd>shows the chemical structure of batocuproin and batophenantroline; </dd></dl>

<dl><dt>Fig. 21 </dt><dd>shows the chemical structure of MeO-TPD and di-NPB; and</dd></dl>

<dl><dt>Fig. 22 </dt><dd>shows a current / voltage characteristic with illumination for a solar cell according to Example 8; </dd></dl>

<dl><dt>Fig. 23 </dt><dd>shows a comparison of an optimized solar cell according to Example 3 with a photoactive heterounion between DCV5T and C60 with p-doped diNPD as a transporter of holes (rectangles) with an analogous structure based on a photoactive heterounion constituted by phthalocyanine phthalocyanine </dd></dl>

The AD-A'-BCO / DA-D'-BCO oligomers (conjugated acceptor-donor-acceptor oligomers (A-DA 'oligomers) / conjugated donor-acceptor-donor oligomers (DA-D' oligomers) are used as light absorbing material, electron conductor (ETM - "electron transport material") or light absorbing material, hollow conductor (HTM - "hole transport material") in organic photoactive components with a photoactive heterounion in various designs. In them, the hollow conductive material (HTM) forms the heterojunction donor and the electron conductive material (ETM) the heterounion acceptor.

Fig. 1 shows a schematic representation of an organic photoactive component with a contact 1 and a countercontact 2 as well as an organic zone 3 electrically connected to the contact 1 and the countercontact 2, a photoactive zone 4 being formed in the organic zone 3 photoactive heterounion 5 between an electron-conducting organic material 6 and a hollow-conducting organic material 7.

If the AD-A'-BCO is used as a hollow conductive material (HTM), the associated electron conductive material (ETM), for example fullerene C60, will be selected such that after the excitation of the AD-A'- BCO by light produces a rapid electron transition to the electron conducting material (ETM). If the AD-A'-BCO is used upside down as an electron conductive material (ETM), the complementary hollow conductive material (HTM) will be selected in such a way that after excitation of the AD-A'-BCO by light there is a rapid transition of holes to the conductive material of holes (HTM).

Heterounion 5 between the electron conductive material 6 and the hollow conductive material 7 is designed as a flat heterounion, if the electron conductive material and the hollow conductive material 6, 7 are formed by a substantially continuous zone between the two zones. of material, that is, an area consisting of an electron conducting material 6 and a hollow conductive material 7.

The heterounion 5 between the electron conducting material and the hole conducting material 6, 7 is a volume heterounion, if the electron conducting material 6 and the hole conducting material 7 are mixed at least in part, so that the interface between the electron conducting material and the hole conducting material 6, 7 comprises a large number of interface sections distributed over the volume of the mixture of materials.

The photoactive zone 4 with the photoactive heterounion 5 between an AD-A'-BCO and an acceptor material (electron conducting material) can be designed as a structure MiM, pin, Mip or Min (M = metal, p = semiconductor p - organic or inorganic doped, n = semiconductor organic or inorganic doped, i = intrinsically conductive system of organic layers).

A design can be envisioned as tandem cells, which are known as such (see P. Peumanns et al., J. Appl. Phys., 93 (7), 3693-3723 (2003): US 4,461,922; US 6,198. 091; US ​​6,198,092). Tandem cells consisting of two or more MiM, pin, Mip or Min diodes stacked on top of each other are also possible (see DE 103 13 232).

The photoactive component is prepared in several designs by depositing the layers by thermal evaporation in a

-6 -8

high vacuum installation at a basic pressure between 10 and 10mbar. Organic materials evaporate from ceramic sources heated by resistance wires. Metal contacts evaporate from molybdenum or ceramic vessels heated directly by current flow through the vessel. The deposition rate is measured and controlled by means of monitors with oscillating quartz. The mixed layers are prepared by simultaneous deposition of a substrate from several sources heated separately and controlled by means of several oscillating quartz monitors. The organic materials used were previously purified by sublimation under high vacuum in a temperature gradient oven.

A simple representative of the AD-A'-BCO group is DCV3T. Fig. 5 shows examples of the chemical structure of bis (dicyanovinylene) oligothiophene derivatives, in which n ≥ 1 and R1-R4 are any radical, preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals:

DCV3T: R1, R2 and R3 = hydrogen, R4 = butyl and n = 1;

DCV5T: R1, R2 and R3 = hydrogen, R4 = butyl and n = 2;

DCV7T: R1, R2 and R3 = hydrogen, R4 = butyl and n = 3;

TCV3T: R1 = nitrile, R2 and R3 = hydrogen, R4 = butyl and n = 1;

Alkyl radicals include methyl, ethyl, propyl, butyl, pentyl, hexyl or the like, which may also be branched, for example as tert-butyl. Examples of aryl radicals include phenyl, naphthyl or also heterocycles with nitrogen or sulfur or oxygen in the ring. In the alkyl, alkoxy and aryl radicals, the peripheral hydrogen atoms may be partially or completely substituted by halogen atoms or nitrile groups.

Compared to the spectrum of dissolved molecules, the absorption spectrum of thin layers of DCV3T shows the desired redshift (see Fig. 3). It is a conjugated AD-A 'oligomer, which manifests itself by comparing it with tertiophene (3T) without DCV terminal groups. Since the electrochemical reduction of 3T cannot be measured, the character of AD-A 'is most clearly shown in the extreme red shift of 3T absorption against DCV3T with a simultaneous increase in oxidation potential first (see the Table 1).

Fig. 3 shows an absorption spectrum of DCV3T in solution (circles) and in a layer deposited with a thickness of 30 nm on quartz crystal (quadrangle). In the layer, the spectrum is shifted towards the longer wavelengths (redshift). The pronounced structure of the spectrum in the layer is an indication that the monomer rings in the oligomer have been made in a manner that is more flat, which is advantageous for high mobility of the load carriers, since it favors the orbital overlap π of adjacent molecules.

Table 1

<dl><dt>Tertiophene (3T) </dt><dd>DCV3T </dd></dl>

<dl><dt>First absorption peak in CH2Cl2 (wavelength in nm and energy in eV) </dt><dd>336 nm: 3.69 eV 500 nm; 2.48 eV</dd></dl>

<dl><dt>First reduction peak in CH2Cl2 (vs. Fc / Fc +) </dt><dd>Not observable in CH2Cl2 (i.e. &lt;-1.7 V) -1.32 V </dd></dl>

<dl><dt>First oxidation peak in CH2Cl2 (vs. ~ Fc / Fc +) </dt><dd>~ +0.7 V (calculated at +1.1 V vs. Ag / AgCl) +0.98 V </dd></dl>

Fig. 4 shows a crystalline structure of DCV3T. The large displacement of the oligomers in the stack favors an attractive interaction between the dipole transition moments when being excited in phase and therefore a redshift of the allowed optical transitions compared to the absorption of the solution. The interaction between the dicyanovinyl acceptor units and the thiophene rings of the nearest neighbors has been indicated with arrows.

Fig. 5 shows a general structure sequence for ADA oligomers conjugated to an extended donor block with specular or point symmetry and dicyanovinylenes as the acceptor group, in which n ≥ 1 and R1-R4 are any radicals, preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals. The donor monomers D1-Dn and Dk used in the donor block in any order can be, for example, the monomers shown in Fig. 6.

Fig. 6 shows additional examples of donor monomers that can be used in AD-A'-BCO or DA-D'-BCO. In this case, X and Y are CR1 or N, Z are S, CO, CR1R2, NR1, in which R1 and R2 are any radical, preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals. Units c) and f) have only a limited donor character and can occur in combination with stronger donor units also with an acceptor function in the AD-A '/ DA-D' oligomers. In addition to the donor groups represented, vinyl, phenyl, naphthyl, anthrazen or other homo- or heterocycles may also be used. Binding to the adjacent monomer in the oligomer is preferably carried out through the indicated links with broken lines, but also at any other site carrying a peripheral hydrogen or an R radical. If a link indicated here with an interrupted line is not used for a junction with an adjacent molecule, any radical R appears again.

Fig. 7 shows examples of units of the acceptor type based on the dioxaborine group that can be used in AD-A'-BCO or DA-D'-BCO. In the AD-A'-BCO according to Fig. 5, said units can replace, for example, the dicyanovinylene terminal groups. R is any radical, but preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals. All other peripheral hydrogen atoms can also be substituted by any radical R. Binding to the adjacent monomer in the oligomer is preferably performed through the bonds indicated with interrupted lines, but can also be performed at any other site carrying a peripheral hydrogen or an R radical. If a link indicated here with an interrupted line is not used for a union with an adjacent molecule, any radical R appears again.

The absorption edge of AD-A'-BCO can be adjusted by selecting donor blocks. A redshift of absorption takes place, for example, when monomer donors from donors with a LUMO lower than in embodiments b), c) and f) are incorporated in Fig. 6.

Fig. 8 shows additional examples of groups of acceptors that can be used in AD-A'-BCO. X is an oxygen or sulfur atom, Y is S or NR, R is any radical, but preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals. The oligothiophene units in the c, e and g molecules in Fig. 8 have an acceptor character due to the quinoid structure. Binding with the adjacent monomer in the oligomer is preferably carried out through the bonds indicated with broken lines, but can also be performed at any other site carrying a peripheral hydrogen or an R radical. If a link indicated here with an interrupted line does not it is used for a union with an adjacent molecule, any radical R occurs here again.

Fig. 9 shows examples of conjugated ADA oligomers in which particularly strong donor units are incorporated at both ends of the extended donor block. Here Y1 and Y2 are oxygen or sulfur atoms, R1-R6 are any radicals, but preferably hydrogen or halogen, nitrile, alkyl, alkoxy or aryl radicals.

Fig. 10 shows examples of DAD-BCO structures with an extended acceptor block. Instead of the represented EDOT group, which has a particularly strong donor character, other donor units can also be used, for example the donor units represented in Fig. 6. Similarly, all units can be used as acceptor monomer of Figs. 7 and 8.

Fig. 11 shows examples of DA-D'-BCO with donor blocks extended at both ends. The peripheral hydrogen atoms may be partially or completely substituted by any radicals, but preferably by halogen, nitrile, alkyl, alkoxy or aryl radicals. Other donor blocks may also be used, for example any combination of the units depicted in Fig. 6. Likewise, all units of Figs. Can be used as acceptor monomer. 7 and 8.

Fig. 12 shows examples of AD-A'-BCO with acceptor blocks extended at both ends, in which n&gt; 0, m&gt; 1, k&gt; 1. Peripheral hydrogen atoms may be partially or completely substituted by halogen, nitrile, alkyl, alkoxy or aryl radicals. Other donor units may also be used, for example any combination of the units depicted in Fig. 6. Likewise, any combination of the units of Figs. Can be used as acceptor monomer. 7 and 8. R is any radical, preferably hydrogen, halogen, nitrile, alkyl, alkoxy or aryl radicals.

Fig. 13 shows absorption spectra in dichloromethane solution and for a deposited layer of DCV-2T-TPy-2T-DCV, a derivative of DCV5T with a thienopyrazine group in the donor block, as well as the structural formula of DCV- 2T-TPy-2T-DCV.

Next, preferred embodiments of organic photoactive components with a structure according to Fig. 1 based on AD-A'-BCO will be described.

Example 1

In a first example, DCV3T is used (see the structure in Fig. 5 with n = 1 and the radical R1 = hydrogen atom) as an acceptor molecule in a heterojunction with N, N, N ', N'-tetrakis ( 4-methoxyphenyl) benzidine (MeOTPD) as a donor molecule. A possible layer sequence for such a heterounion, incorporated into a Mip structure, is as follows: crystal substrate / ITO / C60 (optionally as electron transport layer) / DCV3T / MeOTPD / MeOTPD p-doped / phthalocyanine p-doped zinc (ZnPc; optionally to improve ohmic contact) / gold.

Since MeOTPD is substantially transparent and the junction between C60 and DCV3T is not suitable for exciton separation, the photocurrent generation comes exclusively from the absorption of light in DCV3T, followed by the separation of excitons at the interface between DCV3T and MeOTPD.

Fig. 14 shows a current / voltage characteristic with illumination for a solar cell with a layer of DCV3T with a thickness of 20 nm and a layer of pure MeO-TPD with a thickness of 5 nm, which provide the interface that separates the excitons The exact layer sequence and characteristic data of the illuminated solar cell have also been indicated in Fig. 14. The S shape of the characteristic around the value of +1 V has to do with ITO deficient electron injection into DCV3T. This problem can be overcome by incorporating an intermediate n-doped layer with an appropriate position of the Fermi level.

Example 2

In a second example, a ZnPc layer is used instead of the MeOTPD of Example 1, so that the sequence of layers is as follows: crystal substrate / ITO / C60 (optionally as electron transport layer) / DCV3T / ZnPc / MeOTPD p-doped / ZnPc p-doped ( optionally to improve ohmic contact) / gold.

Fig. 15 shows the current / voltage characteristic with and without illumination for a solar cell with a DCV3T layer with a thickness of 20 nm and a ZnPc layer with a thickness of 10 nm. These layers form the interface that separates the excitons. The exact layer sequence and characteristic data of the illuminated solar cell have also been indicated in Fig. 15.

The mode of operation corresponds to that of Example 1 above. Additionally, a photocurrent generation by light absorption on ZnPc and a separation of excitons in the heterojunction with DCV3T takes place. This increases the short circuit current (jSC) compared to Example 1 above.

This means that in Examples 1 and 2 AD-A'-BCO DCV3T is used as an acceptor and electron conducting material. The advantageous properties of AD-A'-BCO in relation to its stacking behavior, absorption and exciton dynamics are fully deployed here. However, this type of use is not optimal, since electrons are highly located on the acceptor units, whereby AD-A'-BCO with its short acceptor units is not a good electron conductor. However, for organic photoactive components with a flat heterounion and a thin absorption layer, electron mobility is not as critical as in volume heterojunctions, in which low electron mobility immediately results in high losses due to recombination. . Attempts to prepare solar cells consisting of DCV3T and for example ZnPc or 4P-TPD with a volume heterojunction show, accordingly, low efficiencies below 0.5%.

The use of AD-A'-BCO with acceptor units each of only one monomer in volume heterojunctions is not advantageous. Nor do they serve DA-D'-BCO with a very short acceptor block (m &lt;3), whose use as an electron conductor in volume heterojunctions is also not a good idea, since they do not have an electron wave function sufficiently relocated.

Example 3

In a third example, to increase the absorption of light even more in the red spectral region and to increase the ionization energy, instead of the DCV3T of Example 1, DCV5T is used (see the structure in Fig. 5 with n = 2 and R1 = hydrogen), whereby the following layer sequence is obtained: crystal substrate / ITO / C60 / DCV5T / MeOTPD / MeOTPD p-doped / ZnPc p-doped (optionally to improve ohmic contact) / gold.

It has been found that in the third example, contrary to Examples 1 and 2, the photoactive interface between DCV5T and C60 appears, the AD-A'-BCO DCV5T acting contrary to DCV3T as a dopant in the photoactive heterounion and conductor of gaps . The difference can be explained by the low ionization energy of the DCV5T molecule, which comprises the longest donor block.

Fig. 16 shows a current / voltage characteristic with and without illumination for a solar cell with a layer of C60 with a thickness of 20 nm and a layer of DCV5T with a thickness of 15 nm, which act here as active materials. The sequence of layers has been indicated in the insert. The cell reaches an open circuit voltage of 0.94 V, a short-circuit current density of approximately 6 mA / cm2 and therefore an efficiency of approx. 1.8% An identical solar cell in relation to the other points, in which the 15 nm DCV5T was replaced by a dihexylquinquethiophene (DH5T), that is, by a conventional donor oligomer, only reaches an open circuit voltage of 0.34 V , a short circuit current density of approx. 3.1 mA / cm2 and therefore an efficiency of approx. 0.4%, whose photocurrent comes almost exclusively from absorption due to C60.

Fig. 17 shows a) absorption spectra of DCV5T as a layer deposited by evaporation of pure DCV5T, as a mixed layer with C60 (1: 1) and dissolved in CH2Cl2. Clearly visible is the displacement of absorption peaks by changing the DCV5T from the liquid to the solid phase. In addition, Fig. 17 shows b) a fluorescence spectrum of pure DCV5T and a mixed layer consisting of DCV5T and C60 (1: 1). In the spectrum of the mixed layer, it can be seen that the fluorescence of DCV5T is extinguished by the C60.

Fig. 18 shows an external quantum efficiency of the solar cell measured in Fig. 16. It can be seen that the absorption of DCV5T contributes more to the solar cell current, relative to its proportion (see quantum yields at 550-600 nm).

Example 4

In a fourth example, for longer oligothiophene units (for example DCV6T, structure in Fig. 5 with D1 = D3 = thiophene, D2 = dibutylthiophene and R1 = hydrogen or optionally with an electron-donor radical R - for example alkyl group or alkoxy - to ensure a sufficiently low electronic affinity), the ionization energy drops further, whereby said AD-A'-BCO can also be used as a donor molecule in combination with C60 as an acceptor molecule. An exemplary layer sequence for such a heterounion incorporated into a Mip structure is the following: crystal substrate / ITO / C60 / DCV6T / p-doped MeOTPD / ZnPc pdopada (optionally to improve ohmic contact) / gold.

Fig. 19 shows a current / voltage characteristic with simulated sunlight illumination of 127 mW // cm2 for solar cells based on a photoactive heterojunction between C60 and DCV6T designed as flat heterounion (solid line) or volume heterounion (line interrupted - see Example 5 below).

Example 5

In a fifth example, to increase the active interface, a mixed layer of C60 and DCV6T is used in the structure of Example 4 as a volume heterojunction instead of the flat heterojunction. The following sequence of layers is obtained: crystal substrate / ITO / C60 * DCV6T (volume ratio between 4: 1 and 1: 1) / p-doped MeOTPD / p-doped ZnPc (optionally to improve ohmic contact) / gold .

Example 6

All of the above-mentioned active layer systems can also be incorporated into structures without doped layers provided in place of the Mip cells. An advantageous embodiment consists in using the active system of Example 4 with the following structure: glass substrate / ITO / 3,4-polyethylenedioxythiophene: polystyrene sulphonate (PEDOT: PSS; optionally as a conductive layer of polymeric voids) / DCV6T / C60 / optionally a layer to improve contact, for example batocuproin, batophenantroline or LiF / aluminum.

Fig. 20 shows the chemical structure of batocuproin and batophenantroline.

Example 7

According to a seventh example, a pin structure is provided. For example, the following layer structure was selected: crystal substrate / ITO / MeOTPD p-doped / C60 * DCV6T (volume ratio between 4: 1 and 1: 1) / C60 doped / aluminum.

Example 8

An eighth example refers to an advantageous variant of Example 3. In this case, the photoactive heterojunction between C60 and DCV5T is incorporated into the following structure pii: crystal substrate / ITO / HTL p-doped / HTL without doping / DCV5T / C60 / BPhen / A1, HTL meaning a void transport material with a large gap between bands such as MeO-TPD or di-NPB.

Fig. 21 shows the chemical structure of MeO-TPD (above) and di-NPB (below).

Fig. 22 shows a current / voltage characteristic with simulated sunlight illumination of 127 mW // cm2 for solar cells according to Example 8 based on a photoactive heterojunction between C60 and DCV5T in a pii structure with MeO-TPD or di -NPB (see Fig. 21) as a material for transporting holes. The solar cell with di-NPB achieves an energy efficiency of approx. 3% for simulated sunlight.

Fig. 23 shows a comparison of an optimized solar cell according to Example 3 with a photoactive heterojunction between DCV5T and C60 with p-doped diNPD as a transporter of holes (rectangles) and an analogous structure based on a photoactive heterojunction consisting of phthalocyanine zinc (ZnPc) and C60 (triangles). The DCV5T cell has an almost double efficiency of approx. 4.3%, although a mixed layer of ZnPc and C60 with a thickness of 10 nm has been incorporated into the solar cell of ZnPc / C60, in order to increase the photocurrent. Without such addition, the photocurrent in the ZnPc / C60 cell decreases to approx. 6 mA / cm2.

Example 9

In a ninth example, to increase the photocurrent even further, flat heterojunctions have been combined with volume heterojunctions, for example forming the following structure: pdopated crystal substrate / ITO / MeOTPD / DCV6T / C60 * DCV6T (volume ratio between 4: 1 and 1: 1) / C60 / C60 n-doped / aluminum.

For example, herein, excitons excited in the pure DCV6T layer may diffuse to the adjacent mixed layer, where they are separated into pairs of free charge carriers upon bumping with C60 molecules. The same goes for the excitons generated in the pure C60 layer.

In a combined heterojunction, such as that of Example 8, different materials may also be combined to further broaden the excitation spectrum: p-doped crystal substrate / ITO / MeOTPD / EDOT-DCV5T / C60 * DCV6T (volume ratio between 4 : 1 and 1: 1) / TCV3T / C60 n-doped / aluminum.

The pure layers of EDOT-DCV5T (derived from DCV5T, in which at least one thiophene ring has been replaced in the donor block by the EDOT group (Fig. 6d with Y1 = Y2 = O and R1 = R2 = H ), or TCV3T (see the structure in Fig. 2 with n = 1 and R1 = CN) have been selected such that a transition of the mixed layer to EDOT-DCV5T and a transition of electrons of the mixed layer to TCV3T It is possible without barrier.