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  • H10K30/20—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising organic-organic junctions, e.g. donor-acceptor junctions
  • H10K30/211—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising organic-organic junctions, e.g. donor-acceptor junctions comprising multiple junctions, e.g. double heterojunctions
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B82—NANOTECHNOLOGY
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  • B82Y10/00—Nanotechnology for information processing, storage or transmission, e.g. quantum computing or single electron logic
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  • H10K30/30—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation comprising bulk heterojunctions, e.g. interpenetrating networks of donor and acceptor material domains
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  • H10K85/111—Organic polymers or oligomers comprising aromatic, heteroaromatic, or aryl chains, e.g. polyaniline, polyphenylene or polyphenylene vinylene
  • H10K85/113—Heteroaromatic compounds comprising sulfur or selene, e.g. polythiophene
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  • H10K85/211—Fullerenes, e.g. C60
  • H10K85/215—Fullerenes, e.g. C60 comprising substituents, e.g. PCBM
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  • H10K85/615—Polycyclic condensed aromatic hydrocarbons, e.g. anthracene
  • H10K85/621—Aromatic anhydride or imide compounds, e.g. perylene tetra-carboxylic dianhydride or perylene tetracarboxylic di-imide
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  • H10K30/00—Organic devices sensitive to infrared radiation, light, electromagnetic radiation of shorter wavelength or corpuscular radiation
  • H10K30/50—Photovoltaic [PV] devices
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  • H10K—ORGANIC ELECTRIC SOLID-STATE DEVICES
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  • H10K85/20—Carbon compounds, e.g. carbon nanotubes or fullerenes
  • H10K85/211—Fullerenes, e.g. C60
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  • H10K85/30—Coordination compounds
  • H10K85/341—Transition metal complexes, e.g. Ru(II)polypyridine complexes
  • H10K85/342—Transition metal complexes, e.g. Ru(II)polypyridine complexes comprising iridium
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
  • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
  • Y02E10/00—Energy generation through renewable energy sources
  • Y02E10/50—Photovoltaic [PV] energy
  • Y02E10/549—Organic PV cells

Definitions

• the invention relates to a photoactive component having organic layers, in particular a solar cell, having a layer arrangement which has an electrode and a counterelectrode as well as a series of organic layers which is arranged between the electrode and the counterelectrode.
• Organic solar cells consist of a series of thin layers, which typically have a thickness of between 1 ⁇ m and 1 ⁇ m, of organic materials which are preferably vapor-deposited in vacuo or applied from a solution.
• the electrical contacting is usually carried out by metal layers and / or transparent conductive oxides (TCOs).
• organic-based devices over conventional inorganic-based devices, such as semiconductors such as silicon, gallium arsenide, are the sometimes extremely high optical absorption coefficients of up to 2 ⁇ 10 5 cm -1 , so that there is the possibility of using low material and energy required to produce very thin solar cells. Further technological aspects are the low costs, the possibility of producing flexible large-area components on plastic films, and the almost unlimited possibilities of variation in organic chemistry.
• a solar cell converts light energy into electrical energy.
• solar cells do not directly generate free charge carriers by light, but excitons are first formed, ie, electrically neutral excitation states, namely bound electron-hole pairs. These excitons can only be separated by very high electric fields or at suitable interfaces.
• excitons can only be separated by very high electric fields or at suitable interfaces.
• organic solar cells sufficiently high fields are not available, so that all promising concepts for organic solar cells on the exciton separation at photoakti- Interfaces are based (organic donor-acceptor interface - CW Tang, Appl. Phys. Lett, 48 (2), 183-185 (1986)) or interface to an inorganic semiconductor (see B. O'Regan et al. Nature 353, 737 (1991)). This requires that excitons generated in the bulk of the organic material can diffuse to this photoactive interface.
• a layer contains a colloidally dissolved substance which is distributed so as to form a network through which charge carriers can flow (percolation mechanism).
• the task of light absorption takes over in such a network either only one of the components or both.
• the active 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).
• a layer contains two or more types of organic pigments which have different spectral characteristics (JP 04024970).
• One layer contains a pigment that generates the charge carriers, and in addition a material that carries away the charge carriers (JP 07142751).
• the document US Pat. No. 5,093,698 discloses the doping of organic materials. By adding an acceptor-like or a donor-like dopant, the equilibrium charge carrier concentration in the layer is increased and the conductivity is increased. According to the document US 5,093,698, the doped layers are used as injection layers at the interface with the contact or electrode materials in electroluminescent devices. Similar doping approaches are analogously useful for solar cells.
• the diffusion length is usually very low, for example 3 to 10 nm, because of its short lifetime of about 0.1 to 10 ns (see M. Hoffmann et al., J. of Fluorescence, 5 (2), 217 (1995) or P. Peumans et al., J. Appl. Phys., 93, 3693 (2003)).
• the diffusion length can be significantly greater since these lifetimes are several orders of magnitude longer, from about 1 ⁇ s to about 10 ms (see C. Adachi et al., Appl. Phys. Lett. 79, 2082, (2001). )) exhibit.
• the document DE 103 13 232 describes an organic solar cell in which materials with increased ISC probability are used as a component of an organic heterojunction.
• Other solar cells are based in part on the fact that excitations in fullerene C 60 are most likely to be included in the triplet Pass state and there have high diffusion lengths of about 40 nm (P. Peumans et al., J. Appl. Phys., 93, 3693 (2003)).
• FIG. 1 shows the chemical structure of a typical iridium complex as well as a graphic representation of a phosphorescence emission in the red spectral region and an absorption spectrum of a 20nm thick layer on quartz glass The low-energy absorption band around 550 nm is very weak.
• the object of the invention is to provide a photoactive device with organic layers, in which the efficiency of the energy conversion is improved. Summary of the invention
• the invention includes the idea of providing a photoactive component having organic layers, in particular a solar cell, with a layer arrangement which has an electrode and a counter electrode and a series of organic layers which is arranged between the electrode and the counter electrode, wherein:
• the exciton-collecting layer is a mixed layer containing an organic material (A) and at least one further organic material (B), in which:
• a lowest singlet excitation state for excitons (Sf) of the organic material (A) is higher in energy than a lowest singlet excited state for excitons (Sf) of the further organic material (B), - the further organic material (B) by means of an ISC Mechanism (ISC, inter-
• singlet excitons are formed in triplet excitons with a quantum yield of at least about 20%, preferably at least about 50%, and
• a lowest triplet excitation state for excitons (Tf) of the further organic material (B) is energetically higher than a lowest triplet excited state for
• the exciton-collecting layer (EHL), in which triplet excitons are formed due to light absorption, is obtained as a mixture of an organic material A and at least one further organic material B formed. After excitation of a singlet exciton on the organic material A, the excitation energy is transferred to the further organic material B, which requires that its lowest singlet excited state Sf is lower in energy than the lowest singlet excited state Sf of the organic material A.
• the further organic material B is chosen so that the inter-system crossing is favored, so that on the further organic material B singlet excitons are converted with a probability of at least 50% in triplet excitons on the other organic material B.
• the photoactive interface may be formed to form either holes in the exciton-collecting layer (EHL) and electrons in the exciton-separating layer (ESL) or vice versa.
• the charge carriers formed in this way in the exciton-collecting layer (EHL) are referred to below as "photogenerated charge carriers.”
• the transport of the photogenerated charge carriers may take place within the exciton-collecting layer, preferably on the organic material A or on the further organic material B. If, in an advantageous embodiment of the invention, the photogenerated charge carriers are transported on the organic material A or in the same way on the organic material A and the further organic material B, then the further organic material B is neither required for charge carrier transport nor for exciton transport, which is imperative below with reference to the embodiment 4 is explained in more detail.
• the photogenerated charge carriers in the exciton-collecting layer (EHL) are preferably transported on the further organic material B, which is explained in more detail below with reference to the first to third exemplary embodiments, the concentration of the further organic material B in the organic material A are above a percolation limit to provide closed transport paths for charge carriers available.
• the concentration is advantageously greater than about 15%, preferably greater than about 30%.
• the layer arrangement according to the invention can be used in different embodiments of the invention in solar cells with a MiM, a pin, a mip or a min structure, the following abbreviations apply: M - metal, p - p-doped organic or inorganic Semiconductor, n-n-doped organic or inorganic semiconductor and i-intrinsically conductive system of organic layers (see, for example, J. Drechsel et al., Org. Electron., 5 (4), 175 (2004), Maennig et al., Appl. Phys. A 79, 1-14 (2004)).
• a preferred embodiment of the invention provides for the use of the layer arrangement according to the invention in a tandem cell, as described as such by Peumans et al. (See P. Peumans et al., J. Appl. Phys., 93 (7), 3693-3723 (2003), US 4,4619,22, US 6,198,091 or US 6,198,092).
• the use in tandem cells of two or more stacked MiM, pin, Mip or Min diodes can also be provided (compare DE 10 2004 014046 A1, J. Drechsel et al., Thin Solid Films, 451452, 515-517 (2004)).
• a layer can be selected which serves exclusively for exciton separation and for charge carrier transport, as provided below in Exemplary Embodiment 1. However, it can also be a layer which, moreover, absorbs light and is suitable for converting the resulting states of excitation in the volume or at one of their interfaces into free pairs of charge carriers.
• the exciton-separating layer may comprise a photoactive volume heterojunction, as provided below in Exemplary Embodiment 5 (see G.
• Yu et al. Science, 270 (5243), 1789 (1995), WO 00/33396), or it may be a layer that allows diffusion of singlet or triplet excitons to the interface to the exciton-collecting layer, which is provided in Embodiment 4 below.
• An expedient development of the invention provides that for one or more organic materials (Ci; i> 1), from which the excitons separating layer (ESL) is formed, and for the organic material (A) and the at least one further organic material (B), from which the exciton-collecting layer (EHL) is formed, the following applies:
• HOMO is higher in energy than a respective highest occupied orbital (HOMO) of the organic material (A) and of the at least one other organic material (B); and - A respective lowest unoccupied orbital (LUMO) is energetically higher for all organic materials (Ci) than a respective lowest unoccupied orbital (LUMO) of the organic material (A) or at least one other organic material (B).
• a lowest unoccupied orbital (LUMO) is lower in energy than a respective lowest unoccupied orbital (LUMO) of the organic material (A) and the at least one further organic material (B) and
• a respective highest occupied orbital (HOMO) is energetically lower for all organic materials (Ci) than a respective highest occupied orbital (HOMO) of the organic material (A) or of the at least one further organic material (B).
• An expedient embodiment of the invention may provide that a mass fraction of the organic material (A) in the excitonic layer (EHL) collecting layer is greater than about 30%, preferably greater than about 60%, and more preferably greater than about 90%.
• the lowest unoccupied orbital (LUMO) of the organic material (A) is lower in energy or at most about O.leV higher than the lowest unoccupied orbital (LUMO) of the at least one other organic material (B).
• a preferred development of the invention provides that the highest occupied orbital (HOMO) of the organic material (A) is higher in energy or at most about O.leV lower than the highest occupied orbital (HOMO) of the at least one further organic material (B).
• a preferred embodiment of the invention provides that both a mass fraction of the organic material (A) and a mass fraction of the further organic material (B) in the excitonic layer (EHL) collecting layer is greater than about 15%, preferably greater than about 30%.
• a lowest unoccupied orbital (LUMO) of the organic material (B) is lower in energy or at most approximately O.leV higher than the lowest unoccupied orbital (LUMO) of the organic material (A).
• An advantageous embodiment of the invention provides that a highest occupied orbital (HOMO) of the at least one further organic material (B) is higher in energy or at most about O.leV lower than the highest occupied orbital (HOMO) of the organic material (A ).
• a preferred embodiment of the invention provides that a triplet transport layer (TTL) of one or more organic materials is arranged between the exciton-collecting layer (EHL) and the exciton-separating layer (ESL), the energy of a lowest Triplet excited state of the triplet transport layer is less than or equal to the energy of the lowest triplet excited state of the organic material (A) in the excitonic convergent layer (EHL).
• TTL triplet transport layer of one or more organic materials
• a preferred embodiment of the invention provides that a highest occupied orbital (HOMO) of the triplet transport layer (TTL) is energetically equal to or lower than the respective highest occupied orbital (HOMO) of the organic material (A) or of the at least one further organic material in the excitonic layer (EHL) which forms as a mixed layer.
• HOMO highest occupied orbital
• a lowest unoccupied orbital (LUMO) of the triplet transport layer (TTL) is energetically equal to or higher than the lowest unoccupied orbital (LUMO) of the organic Material (A) or the at least one other organic material in the running as a mixed layer excitons layer (EHL).
• An advantageous embodiment of the invention provides that in the at least one further organic material (B), an energy difference between the lowest singlet excitation state for excitons (S 1 5 ) and the lowest triplet excited state for
• the at least one further organic material (B) is from one of the following material classes:
• Fullerenes or carbon nanotubes in particular C 60 , C 70 or C 84 and their derivatives; - Metal-organic compounds, in particular those whose lowest excited state at least partially an excitation of an electron from the metal to the ligand (MLCT - "metal-to-ligand charge transfer") or ligand to metal (LMCT - "ligand-to-metal charge transfer "); and
• Phosphorescent materials having a phosphorescence quantum yield greater than about 0.1%, preferably greater than about 1% in dilute solution.
• a preferred embodiment of the invention provides that the metal-organic compound comprises a heavy metal having an atomic number of greater than 21, preferably greater than 39.
• the organometallic compound comprises a metal from the following group of metals: Ru, Pd, Ag, Cd, In, Sn, Ta, W, Re, Os, Ir, Pt, Au, Hg, Ti, Pb, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Er, Tm, Yb or Lu, preferably Ru, Rh, Re, Os, Ir or Pt.
• an advantageous embodiment of the invention provides that the organic material (A) in the excitonic convergent layer (EHL) is an oligothiophene derivative, a perylene derivative, in particular a derivative of perylenetetracarboxylic dianhydride, perylenetetracarboxylic diimide or perylenetetracarboxylic bisimidazole, or a phthalocyanine ,
• the exciton-separating layer (ESL) is formed as a light-absorbing and singlet and / or triplet excited states generating layer, wherein generated singlet and / or triplet excitation states to the interface between the excitons collecting Layer (EHL) and the exciton separating layer (ESL) diffuse and can be converted there into pairs of charge carriers.
• the exciton-separating layer is a mixed layer containing a plurality of organic materials, in which: a lowest singlet excitation state for excitons of one of the plurality of organic materials is higher than a lowest singlet excited state for excitons Excitons of another of the several organic materials;
• the further organic material is formed so that it is formed with a quantum yield of at least 20%, preferably at least 50% by means of an ISC mechanism (ISC -, Intersystem Crossing ”) singlet excitons in triplet excitons transforming;
• ISC Intersystem Crossing
• a lowest triplet excited state for excitons of the further organic material is higher in energy than a lowest triplet excited state for excitons of the one organic material.
• a photoactive volume-donor-acceptor heterojunction may be formed in the excitonic separating layer (ESL) in the form of a mixed layer by means of the one organic material and the at least one further organic material.
• An advantageous embodiment of the invention provides that an interface of the exciton-collecting layer (EHL), which faces away from the interface with the exciton-separating layer (ESL) / triplet transport layer (TTL), has a triplet block layer (TBL ) is energetically higher in the energetically lowest-energy triplet excitation states than low-energy triplet excitation states in the exciton-collecting layer (EHL).
• EHL exciton-collecting layer
• TTL triplet transport layer
• TBL triplet block layer
• the contact and / or the mating contact are semitransparent or transparent.
• a preferred embodiment of the invention provides that a p-doped layer is arranged between the contact and the photoactive region (M-i-p component).
• an n-doped layer is arranged between the mating contact and the photoactive region (M-i-n device or n-i-p device).
• An advantageous embodiment of the invention provides that one or more layers in the organic region by means of thermal evaporation in a high vacuum or evaporation of organic materials in an inert carrier gas, which transports the organic materials to a substrate ("Organic Vapor Phase Deposition '') deposited are.
• a preferred embodiment of the invention provides that one or more layers are deposited in the organic region from a liquid solution, in particular by spin coating, knife coating or printing.
• a preferred embodiment of the invention provides that the excitons collecting layer (EHL) has a thickness between about 5nm and about 200nm.
• the excitons collecting layer (EHL), the exciton separating layer (ESL) and / or the triplet transport layer (TTL) from a donor-acceptor donor oligomer or a Acceptor-donor-acceptor oligomer are formed.
• FIG. 4 shows a schematic representation with energy levels for explaining the mode of operation of a photoactive component according to a first exemplary embodiment with an exciton-collecting layer of a mixture of DCV3T and C 60 and an exciton-separating layer of MeOTPD;
• Figure 5 is a graphical representation of absorption and Photolumineszenzmess harbor a function of the wavelength for a DCVIT-Emzel Anlagen having a thickness of 20 nm, a DCV3T.
• FIG. 7 is a current-voltage characteristic under illumination with simulated sunlight intensity of 127 W / cm 2 and without illumination for a photoactive component according to a second exemplary embodiment with a 30 nm-thick mixed layer of DCV3T and C 60 (1: 2) collecting as exciton layer and tetramethoxy-tetraphenyl benzidine (MeOTPD) as exciton separating layer;
• Figure 8 is a graph showing the wavelength dependence of external quantum efficiency (EQE - "external quantum efficiency.
• Fig. 10 Structural formulas for a class of compounds that can be used as organic material A in an exciton-collecting layer, with a radical R
• an alkyl group or a cyano group and the group X in the oligothiophene chain may be one of the groups a) to d) or another homo- or heterocyclic compound having a conjugated ⁇ -electron system.
• a layer arrangement which has an electrode and a counterelectrode and a sequence of organic layers which is arranged between the electrode and the counterelectrode.
• Two adjoining layers are formed in a photoactive region encompassed by the sequence of organic layers, namely an exciton-collecting layer (EHL) and an exciton-separating layer (ESL).
• the exciton-collecting layer (EHL) is a mixed layer containing an organic material A and another organic material B.
• a lowest singlet excited state for excitons (Sf) of the organic material (A) is higher in energy than a lowest singlet. Excitation state for excitons (Sf) of the further organic material B.
• the further organic material B converts with high quantum yield of at least about 20%, preferably of at least about 50%, singlet excitons by means of an ISC mechanism (ISC). Furthermore, the mixed layer is designed so that a lowest triplet excitation state for excitons (Tf) of the further organic material B is higher in energy than a lowest triplet excitation state for excitons (T X ⁇ ) of the organic material A, so that the triplet exciton formed on the material B with high probability on the Ma terial A is transferred.
• EHL exciton-collecting layer
• ESL exciton-separating layer
• ITO refers to a transparent base contact of indium tin oxide and C 60 the Buckminster fullerene.
• FIGS. 2 and 3 The structure of the other materials is shown in FIGS. 2 and 3.
• Fig. 2 shows the structural formula of DCV3T.
• the radical R is a hydrogen atom in DCV3T but may also be a cyano group in derivatives (TCV3T, see T. M. Pappenfus et al., Org. Lett, 5 (9), 1535-1538 (2003)) or an alkyl radical.
• Figure 3 shows the chemical structure of MeoTPD (top of Figure 3, MeO denotes a methoxy group) and 4P-TPD (bottom of Figure 3).
• the exciton-collecting layer consists of DCV3T (organic material A) and C 60 (further organic material B) and the exciton-separating layer of MeOTPD.
• FIG. 4 shows a schematic illustration for explaining the mode of operation of a component according to the first exemplary embodiment with an exciton-collecting layer of a mixture of DCV3T and C 60 and an exciton-separating layer of MeOTPD.
• the following subprocesses are shown: (0) excitation of a singlet exciton on DCV3T by light absorption;
• the thus formed triplet excitons on DCV3T can now diffuse to the interface with Me-OTPD and there are separated into free holes on MeOTPD and free electrons on C 60 .
• the lowest unoccupied orbital (LUMO) of the further organic material, C 60 is lower than the lowest unoccupied orbital (LUMO) of the organic material A, namely DCV3T, so that the charge transport of electrons on the further organic material B takes place. This results in the requirement that the additional organic material B must be present in sufficient concentration to provide closed percolation paths available.
• the following layer sequence for the photoactive component is provided: ITO / C 60 / DCV 3 T * C 60 / MeOTPD / p-doped MeOTPD / gold.
• an additional pure C 60 layer is arranged here as a triplet blocking layer (TBL) between the exciton-collecting layer and the ITO electrode
• TBL triplet blocking layer
• the triplet block layer performs the function of preventing triplet excitons diffusing toward the ITO electrode from being quenched there, instead the triplet excitons are reflected at C 60 and have another chance to cross the interface 7 shows a current-voltage characteristic under illumination with simulated sunlight of intensity 127 m W / cm 2 and without illumination for a component according to the second exemplary embodiment with a 30 nm thick mixed layer of DCV3T and C.
• the following layer sequence is provided for the photoactive component: ITO / C 60 / DCV 3 T * C 60 / DCV 3 T / MeOTPD / p-doped MeOTPD / gold.
• an additional triplet transport layer (TTL) of DCV3T (excitatory ion organic material A) is placed between the exciton-collecting layer and the exciton-separating layer
• TTL triplet transport layer
• Excitons collecting layer must here additionally diffuse through the DCV3T layer until it at the Interface to the exciton-separating layer can be separated in holes on MeOTPD and electrons on DCV3T.
• FIG. 8 shows a graph of the wavelength dependence of the external quantum efficiency (EQE), which is shown by a solid line 80, of a photoactive component with the layer sequence ITO / C 60 / DCV3T / Me-OTPD / p-
• the absorption coefficient of C 60 is shown with the aid of a dotted line 82.
• the outer quantum efficiency has a peak at a wavelength of 450 nm, which is due to the absorption coefficient of DCV3T Absorption of the C 60 is due.
• the device according to the third embodiment has the further advantage over the devices according to the first and the second embodiment in that the LUMO of the additional pure DCV3T layer is higher than the LUMO of C 60 .
• charge carrier pairs having a larger free energy are formed at the exciton-separating layer interface, and the device achieves a higher photo-voltage.
• the following layer sequence for the photoactive component is provided: ITO / C 60 / DCV 3 T * C 60 / ZnPc / p-doped MeOTPD / gold.
• ZnPc zinc phthalocyanine
• the excitons photogenerated in ZnPc can be used for excitons Diffuse layer and there are separated into free electrons on C 60 and free holes on ZnPc, so that here also the excitons collecting layer makes a contribution to the photocurrent generation.
• the following layer sequence is provided for the photoactive device: ITO / C 60 / C 60 DCV3T * / 4P-TPD * C 60 (1: 3) / MeOTPD / p-doped MeOTPD / gold.
• a mixed layer of 4P-TPD (see Fig. 3) and C 6 o is provided as an exciton-separating layer.
• the operation of the device according to the fifth embodiment corresponds to that of the device according to the second embodiment.
• 4P-TPD and C 60 in the exciton-separating layer form a volume heterojunction, which in its entire volume can convert excitons formed on either material into charge-carrier pairs, holes on 4P-TPD and electrons on C 60 .
• the excitons separating layer contributes in addition to the photocurrent generation.
• the material 4P-TPD may be replaced by other hole transport materials with greater absorbency, for example, a phthalocyanine or an oligothiophene derivative.
• the following layer sequence for the photoactive component is provided: ITO / TCV3T * C 60 / MeOTPD / p-doped MeOTPD / gold.
• the operation of the device according to the sixth embodiment corresponds to that of the device according to the first embodiment, with the difference that the charge separation at the exciton separating layer for generation of electrons on TCV3T, which is the organic material A of the excitons Layer, and holes on MeOTPD results because here the organic material A has a deeper LUMO as the other organic material B, namely C 60 .
• the transport of triplet excitons and of charge carriers, namely electrons on the organic material A takes place, while the further organic material B serves exclusively to support the ISC. Consequently, the additional organic material B need not provide closed percolation paths in the exciton-collecting layer, and a concentration between about 0.1 and 10% is sufficient. This is an advantage for the photocurrent generation because the organic material A typically has the stronger absorption.
• FIG. 9 shows a schematic representation of the mode of operation of a photoactive component according to the sixth exemplary embodiment. The following sub-processes are shown:
• a thiophene derivative having a structural formula of Fig. 10 or a perylene derivative can be used as the organic material A in the exciton-collecting layer.
• Figure 10 shows structural formulas for a class of compounds that can be used as organic material A in the exciton-collecting layer.
• the radical R may be hydrogen, an alkyl radical or a cyano group.
• the group X in the oligothiophene chain may be one of the groups a) to d) or another homo- or heterocyclic compound having a conjugated ⁇ -electron system.
• the exciton-collecting layer has the function of transporting photogenerated electrons. It therefore preferably has an electron mobility of at least 5.times.10.sup.- 7 cm.sup.-3, but the component can also be designed vice versa so that photogenerated holes are transported in the exciton-collecting layer.
• materials which have an organic material A in the exciton-collecting layer can also be used 10 with suitably chosen radical R, which is preferably hydrogen or an alkyl radical but not electron-withdrawing groups such as CN
• R is preferably hydrogen or an alkyl radical but not electron-withdrawing groups such as CN
• a heavy metal complex can be used, for example a platinum complex (PtK) or an iridium complex (IrK) with a phosphorescence in the infrared spectral range.
• PtK platinum complex
• IrK iridium complex
• the exciton-collecting layer is formed by means of a mixture of DCV5T and IrK, and C 60 forms the exciton-separating layer.
• IrK must be present in the mixed layer in sufficient concentration, namely at least 15%, preferably at least 30%, so that efficient hole transport to IrK can take place.
• An advantageous embodiment is still present if the highest occupied orbital (HOMO) of IrK is higher by a maximum of O.leV than the highest occupied orbital (HOMO) of DCV5T, so that IrK forms a shallow trap for holes in DCV5T. Since the holes can be easily released from the traps by thermal energy, the hole transport can take place on DCV5T, and here too a very low concentration of IrK in DCV5T between about 0.1 and about 10% is sufficient.
• Figure 5 shows absorbance and photoluminescence readings versus wavelength.
• the absorption curve 10 and the course of the photoluminescence 11 are shown as dashed lines.
• the absorption curve 20 and the course of the photoluminescence 21 are shown as dash-dot lines.
• the solid line shows the absorption curve 30 and the course of the photoluminescence 31 for a C 60 single layer with a thickness of 27 nm.
• the luminescence of the single layer of DCV3T at an excitation wavelength of 530 nm is quenched by the presence of C 60 in the DCV 3 T: C 60 mixed layer. Residual luminescence of the mixed layer at an excitation wavelength of 530 nm, which is represented by a factor of 100, results from the weak fluorescence of C 60 , which results from a comparison with the measured values for Cgo single-layer multiplied by a factor of 400. at an excitation wavelength of 512nm. The occurrence of the C 60 fluorescence even when excited by DCV3T the transfer of the singlet excitation energy from DCV3T to C 60 shows.
• Fig. 6 shows the results of a measurement of the so-called "photo-induced absorption" at a measuring temperature of 1OK for a DCV3T layer having a thickness of 20 nm (circles) and for a DCV3T: C 60 mixed layer with a thickness ratio of 20 nm: 27 nm (squares after excitation with an Ar (+) laser at 514 nm with a power density of 30 mW / cm 2 .
• a sample is subjected to periodically modulated illumination, in this case realized by an Ar ion laser, which is directed through a rotating chopper wheel onto the sample, so that this "pump beam” results in a periodic scan varied excitation of the sample and thus to a corresponding oscillating population density of excitation states (excitons).
• a measuring beam of constant intensity is directed onto the sample and the transmission is measured by means of a photodetector beyond the sample. Since excited molecules have a different absorption spectrum than molecules in the ground state, now also the transmission probability of the measuring beam oscillates with the oscillation of the excitation density.
• Figure 6 shows the transmission change normalized to the transmission (.DELTA.T / T
• the modulation of the wavelength of the measuring beam was realized by combining a halogen lamp with a grating monochromator.
• the spectral shape of the photoinduced absorption does not change compared to the pure DCV3T layer; Similarly, the lifetime of the observed excitation is unchanged. However, the measured signal is larger by a factor of 3 compared to the single layer. The magnitude of the observed signal is largely determined by the product of lifetime and population of the state for small frequencies ( ⁇ ⁇ "1) (see, for example, Dellepiane et al., Phys. Rev. B, 48, 7850 (1993); Epshtein et al, Phys. Rev. B, 63, 125206 (2001)).
• ⁇ ⁇ "1 see, for example, Dellepiane et al., Phys. Rev. B, 48, 7850 (1993); Epshtein et al, Phys. Rev. B, 63, 125206 (2001)

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