Dye solar cell with improved stability

Abstract

A photovoltaic element (110) is proposed for conversion of electromagnetic radiation to electrical energy. The photovoltaic element (110) may especially be a dye solar cell (112). The photovoltaic element (110) has at least one first electrode (116), at least one n-semiconductive metal oxide (120), at least one electromagnetic radiation-absorbing dye (122), at least one solid organic p-semiconductor (126) and at least one second electrode (132). The p-semiconductor (126) comprises at least one metal oxide (130).

Claims

1. A photovoltaic element, comprising: a first electrode; an n-semiconductive metal oxide; an electromagnetic radiation-absorbing; a solid organic p-semiconductor; and a second electrode, wherein the solid organic p-semiconductor comprises: a metal oxide; a lithium salt; and an organic matrix material; wherein in the metal oxide the metal is bonded only to an oxygen or another metal, the metal oxide is mixed with the organic matrix material; and a content of the metal oxide in the solid organic p-semiconductor is from 0.5% to 5% by weight, based on a weight of the organic matrix material.

2. The photovoltaic element according to claim 1, wherein the metal oxide is homogeneously distributed in the organic matrix material.

3. The photovoltaic element according to claim 1, wherein the organic matrix material comprises a low molecular weight organic p-semiconductor.

4. The photovoltaic element according to claim 3, wherein the low molecular weight organic p-semiconductor comprises a spiro compound.

5. The photovoltaic element according to claim 3, wherein the low molecular weight organic p-semiconductor is a spiro compound or a compound of structural formula: ##STR00046## in which A.sup.1, A.sup.2, A.sup.3 are each independently divalent organic units which optionally comprise one, two or three substituted aromatic or heteroaromatic groups, where, when two or three aromatic or heteroaromatic groups are present, two of these groups in each case are joined to one another by a chemical bond, via a divalent alkyl residue, or both; R.sup.1, R.sup.2, R.sup.3 are each independently R, OR, NR.sub.2, A.sup.3-OR or A.sup.3-NR.sub.2 substituents; R is alkyl, aryl or a monovalent organic residue which optionally comprises one, two or three substituted aromatic or heteroaromatic groups, where, when two or three aromatic or heteroaromatic groups are present, two of these groups in each case are joined to one another by a chemical bond, via a divalent alkyl or NR residue, or both; R is alkyl, aryl or a monovalent organic residue which optionally comprises one, two or three substituted aromatic or heteroaromatic groups, where, when two or three aromatic or heteroaromatic groups are present, two of these groups in each case are joined to one another by a chemical bond, via a divalent alkyl residue, or both; each n is independently a value of 0, 1, 2 or 3, wherein a sum of each n value is at least 2; and at least two of R.sup.1, R.sup.2 and R.sup.3 residues are substituents OR, NR.sub.2, or both.

6. The photovoltaic element according to claim 1, wherein the metal oxide is at least one member selected from the group consisting of: V.sub.2O.sub.5; Nb.sub.2O.sub.5; MoO.sub.3; MoO.sub.2; MoO.sub.x; VO.sub.x; WO.sub.3; and ReO.sub.3; wherein x in each case is a positive rational number which need not necessarily be an integer.

7. The photovoltaic element according to claim 1, further comprising: an encapsulation, wherein the encapsulation shields the photovoltaic element from a surrounding atmosphere.

8. A process for producing a solid organic p-semiconductor of the photovoltaic element according to claim 1, the process comprising: applying a p-conductive organic matrix material and the metal oxide as a p-dopant together to at least one carrier element from at least one liquid phase.

9. The process according to claim 8, wherein the p-conductive organic matrix material comprises a low molecular weight organic p-semiconductor.

10. The process according to claim 8, wherein the liquid phase further comprises a solvent.

11. The process according to claim 8, wherein the process is performed at least partly in a low-oxygen atmosphere.

12. A process for producing the photovoltaic element according to claim 1, the process comprising: providing the first electrode, the n-semiconductive metal oxide, the electromagnetic radiation-absorbing dye, the solid organic p-semiconductor and the second electrode.

13. The process according to claim 12, wherein the solid organic p-semiconductor is produced by a wet chemical process comprising: applying at least one p-conductive organic matrix material and the metal oxide as a p-dopant together to at least one carrier element from at least one liquid phase; or by a penetration process comprising: applying the at least one p-conductive organic matrix material to a carrier element, and applying the metal oxide to the at least one p-conductive organic matrix material, thereby at least partly penetrating it, or both by a wet chemical process and a penetration process.

14. The photovoltaic element according to claim 1, wherein the metal oxide is mixed by dispersing it into the organic matrix material.

15. The photovoltaic element according to claim 1, wherein the metal oxide is present in the solid organic p-semiconductor from 0.5% to 3%, based on the weight of the organic matrix material.

16. The photovoltaic element according to claim 5, wherein the spiro compound is a spiro-MeOTAD.

17. The photovoltaic element according to claim 7, wherein the encapsulation shields at least one selected from the group consisting of the first electrode, the second electrode, and the solid organic p-semiconductor from a surrounding atmosphere.

18. The photovoltaic element according to claim 1, wherein the metal oxide is at least one oxide of at least one transition group metal and is at least one member selected from the group consisting of ReO.sub.x; WO.sub.x; CeO.sub.2; Ce.sub.2O.sub.3; Ce.sub.3O.sub.4; C.sub.4CeF.sub.12O.sub.12S.sub.4; CeO.sub.2/Gd; CeO.sub.2/Y; CrO.sub.3; Ta.sub.2O.sub.5; a CeZr oxide; Ce(IV) tert-butoxide; Ce(MO.sub.4).sub.3; CeO.sub.4C.sub.10H.sub.36; C.sub.4CeF.sub.12S.sub.4; CeVO.sub.4; and CeO.sub.4Zr.

19. The photovoltaic element according to claim 1, the lithium salt is an organometallic lithium salt.

20. The photovoltaic element according to claim 1, wherein the lithium salt is LiN(SO.sub.2CF.sub.3).sub.2.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) Further details and features of the invention are evident from the description of preferred embodiments which follows in conjunction with the dependent claims. In this context, the particular features may be implemented alone or with several in combination. The invention is not restricted to the working examples. The working examples are shown schematically in the figures. Identical reference numerals in the individual figures refer to identical elements or elements with identical function, or elements which correspond to one another with regard to their functions.

(2) The individual figures show:

(3) FIG. 1 a schematic layer structure of an inventive organic photovoltaic element in a sectional diagram in side view;

(4) FIG. 2 a schematic arrangement of the energy levels in the layer structure according to FIG. 1;

(5) FIG. 3 current-voltage characteristic of a comparative sample without metal oxide, measured 2 days after production;

(6) FIG. 4 current-voltage characteristics of samples with and without metal oxide after different times;

(7) FIG. 5 efficiencies of inventive samples at different times after production; and

(8) FIG. 6 extinction curves of spiro-MeOTAD solutions with and without metal oxide doping.

WORKING EXAMPLES

(9) FIG. 1 shows, in a highly schematic sectional diagram, a photovoltaic element 110 which, in this working example, is a dye solar cell 112. The photovoltaic element 110 according to the schematic layer structure in FIG. 1 can be configured in accordance with the invention. The comparative sample according to the prior art may in principle also correspond to the structure shown in FIG. 1, and differ therefrom, for example, merely with regard to the solid organic p-semiconductor. It is pointed out that the present invention, however, is also usable in other layer structures and/or in other constructions.

(10) The photovoltaic element 110 comprises a substrate 114, for example a glass substrate. Other substrates are also usable, as described above. Applied to this substrate 114 is a first electrode 116, which is also referred to as a working electrode and which preferably, as described above, is transparent. Applied to this first electrode 116 in turn is a blocking layer 118 of an optional metal oxide, which is preferably nonporous and/or nonparticulate. Applied to this in turn is an n-semiconductive metal oxide 120 which has been sensitized with a dye 122.

(11) The substrate 114 and the layers 116 to 120 applied thereto form a carrier element 124 for at least one layer, applied thereto, of a solid organic p-semiconductor 126, which in turn may comprise especially at least one p-semiconductive organic matrix material 128 and at least one metal oxide 130. Applied to this p-semiconductor 126 is a second electrode 132, which is also referred to as the counterelectrode. The layers shown in FIG. 1 together form a layer structure 134 which has been shielded from a surrounding atmosphere by an encapsulation 136, for example in order to completely or partially protect the layer structure 134 from oxygen and/or moisture. One or both of the electrodes 116, 132 may, as indicated in FIG. 1 with reference to the first electrode 116, be conducted out of the encapsulation 136, in order to be able to provide one or more contact connection areas outside the encapsulation 136.

(12) FIG. 2 shows, by way of example, in a highly schematic manner, an energy level diagram of the photovoltaic element 110, for example according to FIG. 1. What are shown are the Fermi levels 138 of the first electrode 116 and of the second electrode 132, and the HOMOs (highest occupied molecular orbitals) 140 and the LUMOs (lowest unoccupied molecular orbitals) 142 of the layers 118/120 (which may comprise the same material, for example TiO.sub.2) of the dye (shown by way of example with a HOMO level of 5.7 eV) and of the p-semiconductor 126 (also referred to as HTL, hole transport layer). The materials specified by way of example for the first electrode 116 and the second electrode 132 are FTO (fluorine-doped tin oxide) and silver.

(13) The photovoltaic elements may additionally optionally comprise further elements. By means of photovoltaic elements 110 with or without encapsulation 136, the working examples described hereinafter were implemented, on the basis of which the effect of the present invention and especially of the p-doping of the p-semiconductor 126 by means of the metal oxide 130 can be demonstrated.

(14) Comparative Sample

(15) As a comparative sample of a photovoltaic element, a dye solar cell with a solid p-semiconductor without metal oxide doping was produced, as known in principle from the prior art.

(16) As the base material and substrate, glass plates which had been coated with fluorine-doped tin oxide (FTO) as the first electrode (working electrode) and were of dimensions 25 mm25 mm3 mm (Hartford Glass) were used, which were treated successively in an ultrasound bath with glass cleaner (RBS 35), demineralized water and acetone, for 5 min in each case, then boiled in isopropanol for 10 minutes and dried in a nitrogen stream.

(17) To produce an optional solid TiO.sub.2 buffer layer, a spray pyrolysis process was used. Thereon, as an n-semiconductive metal oxide, a TiO.sub.2 paste (Dyesol) which comprises TiO.sub.2 particles with a diameter of 25 nm in a terpineol/ethylcellulose dispersion was spun on with a spin-coater at 4500 rpm and dried at 90 C. for 30 min. After heating to 450 C. for 45 min and a sintering step at 450 C. for 30 minutes, a TiO.sub.2 layer thickness of approximately 1.8 m was obtained.

(18) After removal from the drying cabinet, the sample was cooled to 80 C. and immersed into a 5 mM solution of an additive ID662 (see below) for 12 h and subsequently into a 0.5 mM solution of a dye in dichloromethane for 1 h. The dye used was the dye ID504 (see below). After removal from the solution, the sample was subsequently rinsed with the same solvent and dried in a nitrogen stream. The samples obtained in this way were subsequently dried at 40 C. under reduced pressure. ID662 and ID504 have the following structural formulae:

(19) ##STR00005##

(20) Next, a p-semiconductor solution was spun on under a nitrogen atmosphere. For this purpose, a solution of 0.12 M spiro-MeOTAD (Lumtec) and 20 mM LiN(SO.sub.2CF.sub.3).sub.2 (Aldrich) in chlorobenzene was made up. 125 l of this solution were applied to the sample and allowed to act for 60 s. Thereafter, the supernatant solution was spun off at 2000 rpm for 30 s.

(21) Finally, a metal back electrode was applied as a second electrode by thermal metal vaporization under reduced pressure. The metal used was Ag, which was vaporized at a rate of 3 /s at a pressure of approx. 2*10.sup.6 mbar, so as to give a layer thickness of about 200 nm.

(22) After the production, the component was stored under dry air with a relative air humidity of 8% for 2 days. As stated above, it is suspected that this storage brings about oxygen doping of the p-semiconductor, as a result of which the conductivity of the p-semiconductor is enhanced.

(23) To determine the efficiency , the particular current/voltage characteristic was recorded with a source meter model 2400 (Keithley Instruments Inc.) under irradiation with a xenon solar simulator (LOT-Oriel 300 W).

(24) A current-voltage characteristic of the comparative sample is shown in FIG. 3. The short-circuit current (i.e. the current density at load resistance zero) was 9.99 mA/cm.sup.2, the open-circuit voltage V.sub.oc (i.e. the load at which the current density has fallen to zero) was 720 mV, the fill factor was 56% and the efficiency was 4%.

Example 1

V2O5 in Chlorobenzene

(25) As the first working example of an inventive photovoltaic element, the above-described comparative sample was modified by doping the p-semiconductor with vanadium pentoxide, using chlorobenzene as a solvent.

(26) The base material, the preparation thereof, the production of the optional solid TiO.sub.2 buffer layer, the production of the layer of the n-semiconductive metal oxide and the dye sensitization were effected as for the production of the comparative sample.

(27) Next, a p-semiconductor solution was spun on in a glovebox with inert atmosphere. For this purpose, a 0.16 M spiro-MeOTAD (Lumtec) in chlorobenzene p.A. (Sigma-Aldrich) was made up. This was brought into solution in a screwtop bottle at approx. 80 C. on a hotplate. After cooling to room temperature, a 20 mmolar LiN(SO.sub.2CF.sub.3).sub.2 solution in cyclohexanone (hole conductor:lithium salt ratio 33:4) was added to the solution. The addition of lithium salt was followed by a wait time of 3 minutes. The spiro-MeOTAD thus formed, in this example 1, the p-semiconductive matrix material of the p-semiconductor.

(28) For further p-doping of the p-semiconductor and especially of the spiro-MeOTAD matrix material therein, 2.5% vanadium pentoxide (based on the proportion by weight of the p-conductor) were subsequently introduced into the mixture, which was homogenized well by tilting. Without any restriction as to which constituents were now actually in solution, this mixture is also referred to hereinafter as p-semiconductor solution. The concentration figure of the metal oxide should be understood such that the ratio of molar mass of V.sub.2O.sub.5 and spiro-MeOTAD (without additions) is 2.5%. Vanadium oxide was introduced as a powder therein.

(29) After the screwtop bottle had been closed, the p-semiconductor solution was stored in the dark for at least 45 min. This was followed by filtering through a microfilter. 125 l of the solution were applied to the sample and allowed to act for 60 s. Thereafter, the supernatant solution was spun off at 2000 rpm for 30 s.

(30) Finally, in turn, a metal back electrode as the second electrode was applied by thermal metal vaporization under reduced pressure, analogously to the production of the comparative sample.

(31) After the production of this cell, it was sealed to a second glass plate with two-component epoxy adhesive (UHU). In general, the cells were analyzed immediately after production.

Examples 2 to 41

Variations of the Metal Oxides and of the Solvents

(32) Analogously to example 1, further examples of photovoltaic elements were produced, with modification of the metal oxide used and/or the solvent in which the p-semiconductor was dissolved, with respect to example 1.

(33) The production was in principle effected analogously to the above description of example 1. Again, spiro-MeOTAD (Lumtec) was used in each case in a 0.16 M solution, except that the solvents of this solution were varied. Analogously to example 1, the solutions were each brought completely into solution in screwtop bottles at approx. 80 C. on a hotplate. After cooling to room temperature, a 20 mmolar LiN(SO.sub.2CF.sub.3).sub.2 solution in cyclohexanone (hole conductor:lithium salt ratio 33:4) was again added to the solution. The addition of lithium salt was again followed by a wait time of 3 minutes. Subsequently, in each example, 2.5% of the particular metal oxide in each case, again based on the proportion by weight of the p-conductor, was introduced into the mixture, which was homogenized well by tilting. The storage, filtration, application to the sample and spinning off were effected analogously to example 1 above. Subsequently, as in example 1, the metal back electrode was again applied as the second electrode.

(34) For the metal oxides and the solvents, combinations specified below were produced, and current-voltage characteristics were measured for each of the photovoltaic components produced according to the examples. Said combinations are: Example 1: V.sub.2O.sub.2 in chlorobenzene (see above) Example 2: V.sub.2O.sub.2 in cyclohexanone Example 3: CeO.sub.2 in chlorobenzene Example 4: CeO.sub.2 in cyclohexanone Example 5: Ce(MoO.sub.4).sub.3 in chlorobenzene Example 6: Ce(MoO.sub.4).sub.3 in cyclohexanone Example 7: CeO.sub.4C.sub.10H.sub.36 in chlorobenzene Example 8: CeO.sub.4C.sub.10H.sub.36 in cyclohexanone Example 9: CeVO.sub.4 in chlorobenzene Example 10: CeVO.sub.4 in cyclohexanone Example 11: CeO.sub.4Zr in chlorobenzene Example 12: CeO.sub.4Zr in cyclohexanone Example 13: ReO.sub.3 in chlorobenzene Example 14: ReO.sub.3 in cyclohexanone Example 15: MoO.sub.3 in chlorobenzene Example 16: MoO.sub.3 in cyclohexanone Example 17: Ta.sub.2O.sub.5 in chlorobenzene Example 18: Ta.sub.2O.sub.5 in cyclohexanone Example 19: Ta.sub.2O.sub.5 in cyclopentanone Example 20: CeO.sub.2/Y in chlorobenzene Example 21: CeO.sub.2/Gd in chlorobenzene Example 22: C.sub.4CeF.sub.12O.sub.12S.sub.4 in chlorobenzene Example 23: CrO.sub.3 in chlorobenzene Example 24: V.sub.2O.sub.5 in methanol and chlorobenzene

(35) In addition, several analyses were carried out on the above-described comparative sample after different times and storage: Example 25, comparative sample, FIG. 3: chlorobenzene without metal oxide, analyzed 2 days after production Example 26, comparative sample (no figure): as example 42, analysis after two days in dried air.

(36) The current-voltage curves were used in each case to determine the characteristic parameters of short-circuit current J.sub.sc, open-circuit voltage V.sub.oc, fill factor FF and efficiency . The results of these measurements are shown in table 1. In the first column, the abovementioned number of the examples is noted. In the second column, the metal oxide used for doping in each case is listed, in the third column the solvent, in the fourth column (color change) the particular visual impression of the color change in the p-semiconductor solution after addition of the metal oxide, in the fifth column the short-circuit current density J.sub.sc, in the sixth column the open-circuit voltage V.sub.oc, in the seventh column the fill factor, and in the eighth column the efficiency.

(37) TABLE-US-00001 TABLE 1 test results of the evaluation of examples 1 to 26. J.sub.sc Color (mA/ V.sub.oc FF Ex. Metal oxide Solvent change cm.sup.2) (mV) (%) (%) 1 V.sub.2O.sub.2 chlorobenzene dark 12 780 63 6.0 brown 2 V.sub.2O.sub.2 cyclohexanone light 9.37 780 59 4.3 brown 3 CeO.sub.2 chlorobenzene none 10.57 760 52 4.2 4 CeO.sub.2 cyclohexanone none 9.13 800 61 4.4 5 Ce(MoO.sub.4).sub.3 chlorobenzene light 10.45 740 58 4.5 brown 6 Ce(MoO.sub.4).sub.3 cyclohexanone dark 9.22 800 63 4.6 brown 7 CeO.sub.4C.sub.10H.sub.36 chlorobenzene gold 10.63 760 44 3.6 8 CeO.sub.4C.sub.10H.sub.36 cyclohexanone dark 9.25 780 64 4.6 brown 9 CeVO.sub.4 chlorobenzene brown 10.83 740 56 4.5 10 CeVO.sub.4 cyclohexanone gold 9.25 800 60 4.5 11 CeO.sub.4Zr chlorobenzene none 10.3 760 47 3.7 12 CeO.sub.4Zr cyclohexanone brown 8.59 820 63 4.4 13 ReO.sub.3 chlorobenzene dark 8.86 760 64 4.3 brown 14 ReO.sub.3 cyclohexanone dark 9.04 800 60 4.3 brown 15 MoO.sub.3 chlorobenzene none 10.23 740 58 4.4 16 MoO.sub.3 cyclohexanone light 9.14 780 53 3.8 brown 17 Ta.sub.2O.sub.5 chlorobenzene none 9.67 760 61 4.5 18 Ta.sub.2O.sub.5 cyclohexanone none 9.55 780 58 4.3 19 Ta.sub.2O.sub.5 cyclopentanone none 9.47 780 47 3.5 20 CeO.sub.2/Y chlorobenzene light 7.6 820 53 3.3 brown 21 CeO.sub.2/Gd chlorobenzene light 7.6 800 53 3.2 brown 22 C.sub.4CeF.sub.12O.sub.12S.sub.4 chlorobenzene dark 6.6 640 63 2.7 brown 23 CrO.sub.3 chlorobenzene light 8.1 800 56 3.6 brown 24 V.sub.2O.sub.5 chlorobenzene dark 2.2 800 61 1.1 methanol brown 25 Comparative chlorobenzene 4.42 740 25 0.8 sample (immediate analysis) 26 Comparative chlorobenzene 9.99 720 56 4 sample (after storage in dry air for 2 days)

(38) The results show that especially the fill factors and efficiencies of the inventive photovoltaic components are at least comparable and in some cases even considerably exceed the corresponding values of the above-described comparative example, especially the values of the comparative example (example 25). Only after the samples of the comparative example have been stored under air for the purpose of p-doping of the p-semiconductor are the comparative samples comparable with inventive examples, in terms of their values. However, this means, conversely, that inventive photovoltaic components can be produced with exclusion of air, for example under inert gas. After the production, encapsulation can be undertaken without the sample to be encapsulated already being contaminated significantly with oxygen or moisture, which could, for example, attack and corrode the counterelectrode later in the encapsulated state. However, the production with exclusion of air and the encapsulation can have a very positive effect on the lifetime of the photovoltaic components.

(39) FIG. 4 shows current-voltage characteristics of different samples, which have been recorded at different times after the production. Reference numeral 144 denotes a characteristic of a comparative sample analyzed immediately after production. Reference numeral 146 denotes a characteristic of the comparative sample analyzed after two days of storage under air. Reference numeral 148 denotes a sample with V.sub.2O.sub.5 doping according to example 1 above, analyzed directly after production, and reference numeral 150 an analysis on the sample according to example 1, analyzed after two days of storage under air. The characteristic parameters which have been determined from the curves in FIG. 4 are shown in table 2.

(40) TABLE-US-00002 TABLE 2 Characteristic parameters of the inventive samples and of the comparative samples at different times after production Isc V.sub.oc FF [mA/cm.sup.2] [mV] [%] [%] without V.sub.2O.sub.5 t = 0 4.13 760 26 0.8 without V.sub.2O.sub.5, t = 2 days 9.29 860 55 4.4 with V.sub.2O.sub.5, t = 0 9.71 800 68 5.3 with V.sub.2O.sub.5, t = 2 days 9.56 800 70 5.4

(41) The analysis results show clearly that the inventive samples barely change over time. The comparative samples, in contrast, are subject to a strong time dependence, which might be attributable to doping effects with oxygen.

(42) Even after storage under air, however, the comparative samples do not reach the fill factors and efficiencies of the inventive samples.

(43) In order to demonstrate that the high efficiency of the inventive samples produced has a high long-term stability, efficiencies were additionally determined over a prolonged period. For this purpose, samples according to example 1 above were stored under air over a prolonged period, and efficiencies of these samples were determined at regular intervals. The results of these analyses are shown in FIG. 5, with the efficiencies plotted as a function of time t in days (d). It is evident from these analyses that the efficiencies of the inventive samples virtually do not fall even over a period of nearly one month, and remain at a uniformly high level between 4 and 5%.

(44) As stated above, the p-semiconductor and/or the matrix material thereof can especially be doped by mixing the metal oxide into the p-semiconductor or the matrix material thereof, for example in solution. Alternatively or additionally to the preferred mixing in the liquid phase, the at least one metal oxide, however, can also be introduced into the p-semiconductor in another way. One example is vapor deposition, sputtering or another kind of subsequent or preceding application of the metal oxide to and/or below at least one layer of the p-semiconductor or of the matrix material.

(45) Table 3 shows various tests (examples 27 to 52) in which the method of introduction of the metal oxide and/or the concentration of the metal oxide were altered. In principle, all samples of the examples mentioned in table 3 were produced analogously to example 1 above, with the exception of the introduction of the metal oxide. In the Comment column, the special feature of the sample of the particular example is stated in each case. A thickness figure shows in each case that a layer of the metal oxide was applied by vapor deposition. For example, in example 27, after the application of the spiro-MeOTAD as a p-semiconductor or matrix material, 5 nm of vanadium pentoxide were applied by vapor deposition. In the case of sample 28, in contrast, 0.1% vanadium pentoxide was mixed into the solution, but it was not filtered. In the case of sample 29, both mixing of vanadium pentoxide into the spiro-MeOTAD solution and vapor deposition of 5 nm of vanadium pentoxide onto the spiro-MeOTAD layer were effected. In some of the experiments, the solvents were additionally varied in accordance with the information in table 3. In addition, the concentrations of the vanadium pentoxide were varied. Table 3 again reports the characteristic data of the photovoltaic components produced in this way. The last column describes the light intensity at which the analyses were carried out. The values are reported in % sun, where 100% corresponds to a light intensity of one sun, corresponding to 1000 W/m.sup.2.

(46) TABLE-US-00003 TABLE 3 Comparison of examples with different methods of introduction of the metal oxide and different concentrations of the metal oxide I.sub.sc Sun [mA/ V.sub.oc FF [mW/ Ex. Comment cm.sup.2] [mV] [%] [%] cm.sup.2] 27 Spiro-MeOTAD/5 nm 11.56 720 53 4.4 99.8 V.sub.2O.sub.5 28 Spiro-MeOTAD + 0.1% 8.23 860 55 4.0 96 V.sub.2O.sub.5 not filtered 29 Spiro-MeOTAD + 0.1% 7.79 840 62 4.2 96 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 30 Spiro-MeOTAD + 0.1% 8.02 840 61 4.1 101.2 V.sub.2O.sub.5 filtered 31 Spiro-MeOTAD + 0.1% 7.92 860 63 4.3 99.4 V.sub.2O.sub.5 filtered + 5 nm V.sub.2O.sub.5 32 Spiro-MeOTAD + 0.5% 7.28 840 64 3.9 99.4 V.sub.2O.sub.5 not filtered 33 Spiro-MeOTAD + 0.5% 6.8 860 65 3.8 99.4 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 34 Spiro-MeOTAD + 0.5% 7.63 860 64 4.2 99.4 V.sub.2O.sub.5 filtered 35 Spiro-MeOTAD + 0.5% 7.84 860 64 4.3 99.4 V.sub.2O.sub.5 filtered + 5 nm V.sub.2O.sub.5 36 Spiro-MeOTAD + 1.0% 7.98 840 59 3.9 101.7 V.sub.2O.sub.5 not filtered 37 Spiro-MeOTAD + 1.0% 7.62 860 62 3.9 104.2 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 38 Spiro-MeOTAD + 1.0% 7.93 800 74 4.7 102.9 V.sub.2O.sub.5 filtered 39 Spiro-MeOTAD + 1.0% 7.22 840 64 3.8 101.7 V.sub.2O.sub.5 filtered + 5 nm V.sub.2O.sub.5 40 Spiro-MeOTAD + 2.5% 7.45 860 66 4.1 101.7 V.sub.2O.sub.5 not filtered 41 Spiro-MeOTAD + 2.5% 7.26 860 65 4.0 101.7 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 42 Spiro-MeOTAD in 9.71 800 68 5.3 100 chlorobenzene + 2.5% V.sub.2O.sub.5 43 Spiro-MeOTAD + 2.5% 10.24 780 62 5.0 99.2 V.sub.2O.sub.5/5 nm V.sub.2O.sub.5 44 Spiro-MeOTAD + 5.0% 7.91 860 60 4.1 101.2 V.sub.2O.sub.5 not filtered 45 Spiro-MeOTAD + 5.0% 7.58 840 62 3.9 101.2 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 46 Spiro-MeOTAD + 5.0% 8.07 860 61 4.2 101.2 V.sub.2O.sub.5 filtered 47 Spiro-MeOTAD + 5.0% 7.86 860 60 4.0 101.2 V.sub.2O.sub.5 filtered + 5 nm V.sub.2O.sub.5 48 Spiro-MeOTAD + 10.0% 6.94 880 66 4.0 101.2 V.sub.2O.sub.5 not filtered 49 Spiro-MeOTAD + 10.0% 6.34 880 55 3.1 101.2 V.sub.2O.sub.5 not filtered + 5 nm V.sub.2O.sub.5 50 Spiro-MeOTAD + 10.0% 6.6 880 64 3.7 101.2 V.sub.2O.sub.5 filtered 51 Spiro-MeOTAD + 100% 6.72 880 67 3.9 101.2 V.sub.2O.sub.5 filtered + 5 nm V.sub.2O.sub.5 52 Spiro-MeOTAD in 0.15 300 36 0.0 96.7 toluene/ethanol 10:1 + 1% V.sub.2O.sub.5 in MeOH

(47) The results in table 3 show that the highest efficiencies are achieved when the metal oxide is mixed directly into the liquid phase of the p-semiconductor or of the matrix material and is applied to the carrier element together with the latter. Application of the metal oxide as a separate layer before or after the application of the p-semiconductor or carrier material, in contrast, leads to lower efficiencies. The highest efficiencies were achieved with spiro-MeOTAD in chlorobenzene with an addition of 2.5% vanadium pentoxide.

(48) As further possible parameters for variation, the selection of the metal oxide was varied in a series of experiments. Compounds used as dopants also included those which comprise metals, but not in form. The results of these experiments are shown in table 4.

(49) TABLE-US-00004 TABLE 4 Comparison of examples with different types of metal oxides I.sub.sc Sun [mA/ V.sub.oc FF [mW/ Ex. Comment cm.sup.2] [mV] [%] [%] cm.sup.2] 53 Spiro-MeOTAD without 4.76 700 25 0.8 102 dopant 54 Spiro-MeOTAD/5 nm 11.56 720 53 4.4 99.8 V.sub.2O.sub.5 55 Spiro-MeOTAD + 1% 7.93 800 74 4.7 102.9 V.sub.2O.sub.5 56 Spiro-MeOTAD + 2.5% 10.24 780 62 5.0 99.2 V.sub.2O.sub.5/5 nm V.sub.2O.sub.5 57 Spiro-MeOTAD in 9.71 800 68 5.3 100 chlorobenzene + 2.5% V.sub.2O.sub.5 58 Spiro-MeOTAD in 0.15 300 36 0.0 96.7 toluene/ethanol 10:1 + 1% V.sub.2O.sub.5 in MeOH 59 Spiro-MeOTAD/5 nm 11.75 700 41 3.4 99.8 ReO.sub.3 60 Spiro-MeOTAD + 1% 10.55 740 60 4.7 99.1 V.sub.2O.sub.5/5 nm ReO.sub.3 61 Spiro-MeOTAD + 0.2% 4.81 860 63 2.6 100 ReO.sub.3 62 Spiro-MeOTAD/5 nm 4.32 860 64 2.4 100.3 MoO.sub.3 63 Spiro-MeOTAD/10 nm 4.1 860 61 2.1 102.2 MoO.sub.3/spiro-MeOTAD + 0.01% MoO.sub.3/5 nm MoO.sub.3 64 Spiro-MeOTAD + 0.2% 5.36 840 67 3.0 99.6 MoO.sub.3/5 nm MoO.sub.3 66 Spiro-MeOTAD + 3.0% 10.89 760 52 4.3 100 cerium(III) tungstate in the spiro-MeOTAD 67 Spiro-MeOTAD + 1% 0.4 450 48 0.1 97.8 FeCl.sub.3 68 Spiro-MeOTAD + 1% 1.07 250 31 0.1 98.4 Cl.sub.2Sb

(50) Again, both samples in which the metal oxide or the dopant was mixed into the matrix material of the p-semiconductor and samples in which the dopant was applied separately, before or after application of the p-semiconductor or matrix material, were produced. With regard to the nomenclature of the sample production, which again followed example 1 above with the exception of the production of the p-semiconductor, reference may be made to the description of table 3.

(51) The results shown in table 4 again show firstly that combined application of the metal oxide and of the matrix material from a combined liquid phase is particularly advantageous. The highest efficiency was again found for 2.5% vanadium pentoxide in a combined liquid phase with spiro-MeOTAD with use of chlorobenzene as a solvent (example 74). In addition, the results in table 4 also show, however, that metal oxides have considerably higher efficiencies compared to other metallic compounds, as, for example, in examples 83 and 84.

(52) As a further possible parameter for variation, it was examined in a test series whether the positive effect of doping by metal oxides also occurs in other p-semiconductors, more particularly in other matrix materials with p-semiconductive properties. Accordingly, tests were carried out in which, in example 1 above, the spiro-MeOTAD was replaced by other matrix materials. The results are shown in table 5.

(53) TABLE-US-00005 TABLE 5 Comparison of examples with different p-semiconductors I.sub.sc V.sub.oc FF Ex. Matrix material [MA/cm.sup.2] [mV] [%] [%] 69 ID522, 8.93 855 43 3.3 without V.sub.2O.sub.5 70 ID522, 7.9 720 63 3.6 with V.sub.2O.sub.5 71 ID367, 8.17 760 32 2 without V.sub.2O.sub.5 72 ID367, 8.88 760 55 3.6 with V.sub.2O.sub.5

(54) ID522 refers to an arylamine with the following structural formula:

(55) ##STR00006##

(56) ID367 likewise refers to an arylamine, but with the following structural formula:

(57) ##STR00007##

(58) The results in table 5 show that the positive effect of doping by the metal oxide vanadium pentoxide also occurs in other p-semiconductors or matrix materials. However, the use of spiro compounds appears to be particularly efficient, especially that of spiro-MeOTAD.

(59) Finally, synthesis examples of low molecular weight organic p-semiconductors are also listed hereinafter, which are usable individually or in combination in the context of the present invention and which can, for example, satisfy the formula I given above.

SYNTHESIS EXAMPLES

Synthesis of Compounds of the Formula I

(60) A) Syntheses:

(61) Synthesis Route I:

(62) Synthesis Step I-R1:

(63) ##STR00008##

(64) The synthesis in synthesis step I-R1 was based on the references cited below: a) Liu, Yunqi; Ma, Hong; Jen, Alex K-Y.; CHCOFS; Chem. Commun.; 24; 1998; 2747-2748, b) Goodson, Felix E.; Hauck, Sheila; Hartwig, John F.; J. Am. Chem. Soc.; 121; 33; 1999; 7527-7539, c) Shen, Jiun Yi; Lee, Chung Ying; Huang, Tai-Hsiang; Lin, Jiann T.; Tao, Yu-Tai; Chien, Chin-Hsiung; Tsai, Chiitang; J. Mater. Chem.; 15; 25; 2005; 2455-2463, d) Huang, Ping-Hsin; Shen, Jiun-Yi; Pu, Shin-Chien; Wen, Yuh-Sheng; Lin, Jiann T.; Chou, Pi-Tai; Yeh, Ming-Chang P.; J. Mater. Chem.; 16; 9; 2006; 850-857, e) Hirata, Narukuni; Kroeze, Jessica E.; Park, Taiho; Jones, David; Hague, Saif A.; Holmes, Andrew B.; Durrant, James R.; Chem. Commun.; 5; 2006; 535-537.
Synthesis Step I-R2:

(65) ##STR00009##

(66) The synthesis in synthesis step I-R2 was based on the references cited below: a) Huang, Qinglan; Evmenenko, Guennadi; Dutta, Pulak; Marks, Tobin J.; J. Am. Chem. Soc.; 125; 48; 2003; 14704-14705, b) Bacher, Erwin; Bayerl, Michael; Rudati, Paula; Reckefuss, Nina; Mueller, C. David; Meerholz, Klaus; Nuyken, Oskar; Macromolecules; EN; 38; 5; 2005; 1640-1647, c) Li, Zhong Hui; Wong, Man Shing; Tao, Ye; D'Iorio, Marie; J. Org. Chem.; EN; 69; 3; 2004; 921-927.
Synthesis Step I-R3:

(67) ##STR00010##

(68) The synthesis in synthesis step I-R3 was based on the reference cited below: J. Grazulevicius; J. of Photochem. and Photobio., A: Chemistry 2004 162(2-3), 249-252.

(69) The compounds of the formula I can be prepared via the sequence of synthesis steps shown above in synthesis route I. The reactants can be coupled, for example, by Ullmann reaction with copper as a catalyst or under palladium catalysis.

(70) Synthesis Route II:

(71) Synthesis Step II-R1:

(72) ##STR00011##

(73) The synthesis in synthesis step II-R1 was based on the references cited under I-R2.

(74) Synthesis Step II-R2:

(75) ##STR00012##

(76) The synthesis in synthesis step II-R2 was based on the references cited below: a) Bacher, Erwin; Bayerl, Michael; Rudati, Paula; Reckefuss, Nina; Mller, C. David; Meerholz, Klaus; Nuyken, Oskar; Macromolecules; 38; 5; 2005; 1640-1647, b) Goodson, Felix E.; Hauck, Sheila; Hartwig, John F.; J. Am. Chem. Soc.; 121; 33; 1999; 7527-7539; Hauck, Sheila I.; Lakshmi, K. V.; Hartwig, John F.; Org. Lett.; 1; 13; 1999; 2057-2060.
Synthesis Step II-R3:

(77) ##STR00013##

(78) The compounds of the formula I can be prepared via the sequence of synthesis steps shown above in synthesis route II. The reactants can be coupled, as also in synthesis route I, for example, by Ullmann reaction with copper as a catalyst or under palladium catalysis.

(79) Preparation of the Starting Amines:

(80) When the diarylamines in synthesis steps I-R2 and II-R1 of synthesis routes I and II are not commercially available, they can be prepared, for example, by Ullmann reaction with copper as a catalyst or under palladium catalysis, according to the following reaction:

(81) ##STR00014##

(82) The synthesis was based on the review articles listed below:

(83) Palladium-Catalyzed CN Coupling Reactions:

(84) a) Yang, Buchwald; J. Organomet. Chem. 1999, 576 (1-2), 125-146, b) Wolfe, Marcoux, Buchwald; Acc. Chem. Res. 1998, 31, 805-818, c) Hartwig; Angew. Chem. Int. Ed. Engl. 1998, 37, 2046-2067.
Copper-Catalyzed CN Coupling Reactions: a) Goodbrand, Hu; Org. Chem. 1999, 64, 670-674, b) Lindley; Tetrahedron 1984, 40, 1433-1456.

Synthesis Example 1

Synthesis of the Compound ID367 (Synthesis Route I)

(85) Synthesis Step I-R1:

(86) ##STR00015##

(87) A mixture of 4,4-dibromobiphenyl (93.6 g; 300 mmol), 4-methoxyaniline (133 g; 1.08 mol), Pd(dppf)Cl.sub.2 (Pd(1,1-bis(diphenylphosphino)ferrocene)Cl.sub.2; 21.93 g; 30 mmol) and t-BuONa (sodium tert-butoxide; 109.06 g; 1.136 mol) in toluene (1500 ml) was stirred under a nitrogen atmosphere at 110 C. for 24 hours. After cooling, the mixture was diluted with diethyl ether and filtered through a Celite pad (from Carl Roth). The filter bed was washed with 1500 ml each of ethyl acetate, methanol and methylene chloride. The product was obtained as a light brown solid (36 g; yield: 30%).

(88) .sup.1H NMR (400 MHz, DMSO): 7.81 (s, 2H), 7.34-7.32 (m, 4H), 6.99-6.97 (m, 4H), 6.90-6.88 (m, 4H), 6.81-6.79 (m, 4H), 3.64 (s, 6H).

(89) Synthesis Step I-R2:

(90) ##STR00016##

(91) Nitrogen was passed for a period of 10 minutes through a solution of dppf (1,1-bis(diphenyl-phosphino)ferrocene; 0.19 g; 0.34 mmol) and Pd.sub.2(dba).sub.3 (tris(dibenzylideneacetone)-dipalladium(0); 0.15 g; 0.17 mmol) in toluene (220 ml). Subsequently, t-BuONa (2.8 g; 29 mmol) was added and the reaction mixture was stirred for a further 15 minutes. 4,4-Dibromobiphenyl (25 g; 80 mmol) and 4,4-dimethoxydiphenylamine (5.52 g; 20 mmol) were then added successively. The reaction mixture was heated at a temperature of 100 C. under a nitrogen atmosphere for 7 hours. After cooling to room temperature, the reaction mixture was quenched with ice-water, and the precipitated solid was filtered off and dissolved in ethyl acetate. The organic layer was washed with water, dried over sodium sulfate and purified by column chromatography (eluent: 5% ethyl acetate/hexane). A pale yellow solid was obtained (7.58 g, yield: 82%).

(92) .sup.1H NMR (300 MHz, DMSO-d.sub.6): 7.60-7.49 (m, 6H), 7.07-7.04 (m, 4H), 6.94-6.91 (m, 4H), 6.83-6.80 (d, 2H), 3.75 (s, 6H).

(93) Synthesis Step I-R3:

(94) ##STR00017##

(95) N.sup.4,N.sup.4-Bis(4-methoxyphenyl)biphenyl-4,4-diamine (product from synthesis step I-R1; 0.4 g; 1.0 mmol) and product from synthesis step I-R2 (1.0 g; 2.2 mmol) were added under a nitrogen atmosphere to a solution of t-BuONa (0.32 g; 3.3 mmol) in o-xylene (25 ml). Subsequently, palladium acetate (0.03 g; 0.14 mmol) and a solution of 10% by weight of P(t-Bu).sub.3 (tris-t-butylphosphine) in hexane (0.3 ml; 0.1 mmol) were added to the reaction mixture which was stirred at 125 C. for 7 hours. Thereafter, the reaction mixture was diluted with 150 ml of toluene and filtered through Celite, and the organic layer was dried over Na.sub.2SO.sub.4. The solvent was removed and the crude product was reprecipitated three times from a mixture of tetrahydrofuran (THF)/methanol. The solid was purified by column chromatography (eluent: 20% ethyl acetate/hexane), followed by a precipitation with THF/methanol and an activated carbon purification. After removing the solvent, the product was obtained as a pale yellow solid (1.0 g, yield: 86%).

(96) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.52-7.40 (m, 8H), 6.88-7.10 (m, 32H), 6.79-6.81 (d, 4H), 3.75 (s, 6H), 3.73 (s, 12H).

Synthesis Example 2

Synthesis of the Compound ID447 (Synthesis Route II)

(97) Synthesis Step I-R1:

(98) ##STR00018##

(99) p-Anisidine (5.7 g, 46.1 mmol), t-BuONa (5.5 g, 57.7 mol) and P(t-Bu).sub.3 (0.62 ml, 0.31 mmol) were added to a solution of the product from synthesis step I-R2 (17.7 g, 38.4 mmol) in toluene (150 ml). After nitrogen had been passed through the reaction mixture for 20 minutes, Pd.sub.2(dba).sub.3 (0.35 g, 0.38 mmol) was added. The resulting reaction mixture was left to stir under a nitrogen atmosphere at room temperature for 16 hours. Subsequently, it was diluted with ethyl acetate and filtered through Celite. The filtrate was washed twice with 150 ml each of water and saturated sodium chloride solution. After the organic phase had been dried over Na.sub.2SO.sub.4 and the solvent had been removed, a black solid was obtained. This solid was purified by column chromatography (eluent: 0-25% ethyl acetate/hexane). This afforded an orange solid (14 g, yield: 75%).

(100) .sup.1H NMR (300 MHz, DMSO): 7.91 (s, 1H), 7.43-7.40 (d, 4H), 7.08-6.81 (m, 16H), 3.74 (s, 6H), 3.72 (s, 3H).

(101) Synthesis Step I-R3:

(102) ##STR00019##

(103) t-BuONa (686 mg; 7.14 mmol) was heated at 100 C. under reduced pressure, then the reaction flask was purged with nitrogen and allowed to cool to room temperature. 2,7-Dibromo-9,9-dimethylfluorene (420 mg; 1.19 mmol), toluene (40 ml) and Pd[P(.sup.tBu).sub.3].sub.2 (20 mg; 0.0714 mmol) were then added, and the reaction mixture was stirred at room temperature for 15 minutes. Subsequently, N,N,N-p-trimethoxytriphenylbenzidine (1.5 g; 1.27 mmol) was added to the reaction mixture which was stirred at 120 C. for 5 hours. The mixture was filtered through a Celite/MgSO.sub.4 mixture and washed with toluene. The crude product was purified twice by column chromatography (eluent: 30% ethyl acetate/hexane) and, after twice reprecipitating from THF/methanol, a pale yellow solid was obtained (200 mg, yield: 13%).

(104) .sup.1H NMR: (400 MHz, DMSO-d.sub.6): 7.60-7.37 (m, 8H), 7.02-6.99 (m, 16H), 6.92-6.87 (m, 20H), 6.80-6.77 (d, 2H), 3.73 (s, 6H), 3.71 (s, 12H), 1.25 (s, 6H)

Synthesis Example 3

Synthesis of the Compound ID453 (Synthesis Route I)

(105) a) Preparation of the Starting Amine:

(106) Step 1:

(107) ##STR00020##

(108) NaOH (78 g; 4 eq) was added to a mixture of 2-bromo-9H-fluorene (120 g; 1 eq) and BnEt.sub.3NCl (benzyltriethylammonium chloride; 5.9 g; 0.06 eq) in 580 ml of DMSO (dimethyl sulfoxide). The mixture was cooled with ice-water, and methyl iodide (MeI) (160 g; 2.3 eq) was slowly added dropwise. The reaction mixture was left to stir overnight, then poured into water and subsequently extracted three times with ethyl acetate. The combined organic phases were washed with a saturated sodium chloride solution and dried over Na.sub.2SO.sub.4, and the solvent was removed. The crude product was purified by column chromatography using silica gel (eluent: petroleum ether). After washing with methanol, the product (2-bromo-9,9-dimethyl-9H-fluorene) was obtained as a white solid (102 g).

(109) .sup.1H NMR (400 MHz, CDCl.sub.3): 1.46 (s, 6H), 7.32 (m, 2H), 7.43 (m, 2H), 7.55 (m, 2H), 7.68 (m, 1H)

(110) Step 2:

(111) ##STR00021##

(112) p-Anisidine (1.23 g; 10.0 mmol) and 2-bromo-9,9-dimethyl-9H-fluorene (3.0 g; 11.0 mmol) were added under a nitrogen atmosphere to a solution of t-BuONa (1.44 g; 15.0 mmol) in 15 ml of toluene (15 ml). Pd.sub.2(dba).sub.3 (92 mg; 0.1 mmol) and a 10% by weight solution of P(t-Bu).sub.3 in hexane (0.24 ml; 0.08 mmol) were added, and the reaction mixture was stirred at room temperature for 5 hours. Subsequently, the mixture was quenched with ice-water, and the precipitated solid was filtered off and dissolved in ethyl acetate. The organic phase was washed with water and dried over Na.sub.2SO.sub.4. After purifying the crude product by column chromatography (eluent: 10% ethyl acetate/hexane), a pale yellow solid was obtained (1.5 g, yield: 48%).

(113) .sup.1H NMR (300 MHz, C.sub.6D.sub.6): 7.59-7.55 (d, 1H), 7.53-7.50 (d, 1H), 7.27-7.22 (t, 2H), 7.19 (s, 1H), 6.99-6.95 (d, 2H), 6.84-6.77 (m, 4H), 4.99 (s, 1H), 3.35 (s, 3H), 1.37 (s, 6H).

(114) b) Preparation of the Compound for Use in Accordance with the Invention

(115) Synthesis Step I-R2:

(116) ##STR00022##

(117) Product from a) (4.70 g; 10.0 mmol) and 4,4-dibromobiphenyl (7.8 g; 25 mmol) were added to a solution of t-BuONa (1.15 g; 12 mmol) in 50 ml of toluene under nitrogen. Pd.sub.2(dba).sub.3 (0.64 g; 0.7 mmol) and DPPF (0.78 g; 1.4 mmol) were added, and the reaction mixture was left to stir at 100 C. for 7 hours. After the reaction mixture had been quenched with ice-water, the precipitated solid was filtered off and it was dissolved in ethyl acetate. The organic phase was washed with water and dried over Na.sub.2SO.sub.4. After purifying the crude product by column chromatography (eluent: 1% ethyl acetate/hexane), a pale yellow solid was obtained (4.5 g, yield: 82%).

(118) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.70-7.72 (d, 2H), 7.54-7.58 (m, 6H), 7.47-7.48 (d, 1H), 7.21-7.32 (m, 3H), 7.09-7.12 (m, 2H), 6.94-6.99 (m, 4H), 3.76 (s, 3H), 1.36 (s, 6H).

(119) Synthesis Step I-R3:

(120) ##STR00023##

(121) N.sup.4,N.sup.4-Bis(4-methoxyphenyl)biphenyl-4,4-diamine (0.60 g; 1.5 mmol) and product from the preceding synthesis step I-R2 (1.89 g; 3.5 mmol) were added under nitrogen to a solution of t-BuONa (0.48 g; 5.0 mmol) in 30 ml of o-xylene. Palladium acetate (0.04 g; 0.18 mmol) and P(t-Bu).sub.3 in a 10% by weight solution in hexane (0.62 ml; 0.21 mmol) were added, and the reaction mixture was stirred at 125 C. for 6 hours. Subsequently, the mixture was diluted with 100 ml of toluene and filtered through Celite. The organic phase was dried over Na.sub.2SO.sub.4 and the resulting solid was purified by column chromatography (eluent: 10% ethyl acetate/hexane). This was followed by reprecipitation from THF/methanol to obtain a pale yellow solid (1.6 g, yield: 80%).

(122) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.67-7.70 (d, 4H), 7.46-7.53 (m, 14H), 7.21-7.31 (m, 4H), 7.17-7.18 (d, 2H), 7.06-7.11 (m, 8H), 6.91-7.01 (m, 22H), 3.75 (s, 12H), 1.35 (s, 12H).

(123) Further compounds of the formula I for use in accordance with the invention:

(124) The compounds listed below were obtained analogously to the syntheses described above:

Synthesis Example 4

Compound ID320

(125) ##STR00024##

(126) .sup.1H NMR (300 MHz, THF-d.sub.8): 7.43-7.46 (d, 4H), 7.18-7.23 (t, 4H), 7.00-7.08 (m, 16H), 6.81-6.96 (m, 18H), 3.74 (s, 12H)

Synthesis Example 5

Compound ID321

(127) ##STR00025##

(128) .sup.1H NMR (300 MHz, THF-d.sub.8): 7.37-7.50 (t, 8H), 7.37-7.40 (d, 4H), 7.21-7.26 (d, 4H), 6.96-7.12 (m, 22H), 6.90-6.93 (d, 4H), 6.81-6.84 (d, 8H), 3.74 (s, 12H)

Synthesis Example 6

Compound ID366

(129) ##STR00026##

(130) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.60-7.70 (t, 4H), 7.40-7.55 (d, 2H), 7.17-7.29 (m, 8H), 7.07-7.09 (t, 4H), 7.06 (s, 2H), 6.86-7.00 (m, 24H), 3.73 (s, 6H), 1.31 (s, 12H)

Synthesis Example 7

Compound ID368

(131) ##STR00027##

(132) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.48-7.55 (m, 8H), 7.42-7.46 (d, 4H), 7.33-7.28 (d, 4H), 6.98-7.06 (m, 20H), 6.88-6.94 (m, 8H), 6.78-6.84 (d, 4H), 3.73 (s, 12H), 1.27 (s, 18H)

Synthesis Example 8

Compound ID369

(133) ##STR00028##

(134) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.60-7.70 (t, 4H), 7.57-7.54 (d, 4H), 7.48-7.51 (d, 4H), 7.39-7.44 (t, 6H), 7.32-7.33 (d, 2H), 7.14-7.27 (m, 12H), 7.00-7.10 (m, 10H), 6.90-6.96 (m, 4H), 6.80-6.87 (m, 8H), 3.75 (s, 12H), 1.42 (s, 12H)

Synthesis Example 9

Compound ID446

(135) ##STR00029##

(136) .sup.1H NMR (400 MHz, dmso-d.sub.6): 7.39-7.44 (m, 8H), 7.00-7.07 (m, 13H), 6.89-6.94 (m, 19H), 6.79-6.81 (d, 4H), 3.73 (s, 18H)

Synthesis Example 10

Compound ID450

(137) ##STR00030##

(138) .sup.1H NMR (400 MHz, dmso-d.sub.6): 7.55-7.57 (d, 2H), 7.39-7.45 (m, 8H), 6.99-7.04 (m, 15H), 6.85-6.93 (m, 19H), 6.78-6.80 (d, 4H), 3.72 (s, 18H), 1.68-1.71 (m, 6H), 1.07 (m, 6H), 0.98-0.99 (m, 8H), 0.58 (m, 6H)

Synthesis Example 11

Compound ID452

(139) ##STR00031##

(140) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.38-7.44 (m, 8H), 7.16-7.19 (d, 4H), 6.99-7.03 (m, 12H), 6.85-6.92 (m, 20H), 6.77-6.79 (d, 4H), 3.74 (s, 18H), 2.00-2.25 (m, 4H), 1.25-1.50 (m, 6H)

Synthesis Example 12

Compound ID480

(141) ##STR00032##

(142) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.40-7.42 (d, 4H), 7.02-7.05 (d, 4H), 6.96-6.99 (m, 28H), 6.74-6.77 (d, 4H), 3.73 (s, 6H), 3.71 (s, 12H)

Synthesis Example 13

Compound ID518

(143) ##STR00033##

(144) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.46-7.51 (m, 8H), 7.10-7.12 (d, 2H), 7.05-7.08 (d, 4H), 6.97-7.00 (d, 8H), 6.86-6.95 (m, 20H), 6.69-6.72 (m, 2H), 3.74 (s, 6H), 3.72 (s, 12H), 1.24 (t, 12H)

Synthesis Example 14

Compound ID519

(145) ##STR00034##

(146) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.44-7.53 (m, 12H), 6.84-7.11 (m, 32H), 6.74-6.77 (d, 2H), 3.76 (s, 6H), 3.74 (s, 6H), 2.17 (s, 6H), 2.13 (s, 6H)

Synthesis Example 15

Compound ID521

(147) ##STR00035##

(148) .sup.1H NMR (400 MHz, THF-d.sub.6): 7.36-7.42 (m, 12H), 6.99-7.07 (m, 20H), 6.90-6.92 (d, 4H), 6.81-6.84 (m, 8H), 6.66-6.69 (d, 4H), 3.74 (s, 12H), 3.36-3.38 (q, 8H), 1.41-1.17 (t, 12H)

Synthesis Example 16

Compound ID522

(149) ##STR00036##

(150) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.65 (s, 2H), 7.52-7.56 (t, 2H), 7.44-7.47 (t, 1H), 7.37-7.39 (d, 2H), 7.20-7.22 (m, 10H), 7.05-7.08 (dd, 2H), 6.86-6.94 (m, 8H), 6.79-6.80-6.86 (m, 12H), 6.68-6.73, (dd, 8H), 6.60-6.62 (d, 4H), 3.68 (s, 12H), 3.62 (s, 6H)

Synthesis Example 17

Compound ID523

(151) ##STR00037##

(152) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.54-7.56 (d, 2H), 7.35-7.40 (dd, 8H), 7.18 (s, 2H), 7.00-7.08 (m, 18H), 6.90-6.92 (d, 4H), 6.81-6.86 (m, 12H), 3.75 (s, 6H), 3.74 (s, 12H), 3.69 (s, 2H)

Synthesis Example 18

Compound ID565

(153) ##STR00038##

(154) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.97-8.00 (d, 2H), 7.86-7.89 (d, 2H), 7.73-7.76 (d, 2H), 7.28-7.47 (m, 20H), 7.03-7.08 (m, 16H), 6.78-6.90 (m, 12H), 3.93-3.99 (q, 4H), 3.77 (s, 6H), 1.32-1.36 (s, 6H)

Synthesis Example 19

Compound ID568

(155) ##STR00039##

(156) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.41-7.51 (m, 12H), 6.78-7.06 (m, 36H), 3.82-3.84 (d, 4H), 3.79 (s, 12H), 1.60-1.80 (m, 2H), 0.60-1.60 (m, 28H)

Synthesis Example 20

Compound ID569

(157) ##STR00040##

(158) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.40-7.70 (m, 10H), 6.80-7.20 (m, 36H), 3.92-3.93 (d, 4H), 2.81 (s, 12H), 0.60-1.90 (m, 56H)

Synthesis Example 21

Compound ID572

(159) ##STR00041##

(160) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.39-7.47 (m, 12H), 7.03-7.11 (m, 20H), 6.39-6.99 (m, 8H), 6.83-6.90 (m, 8H), 3.78 (s, 6H), 3.76 (s, 6H), 2.27 (s, 6H)

Synthesis Example 22

Compound ID573

(161) ##STR00042##

(162) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.43-7.51 (m, 20H), 7.05-7.12 (m, 24H), 6.87-6.95 (m, 12H), 3.79 (s, 6H), 3.78 (s, 12H)

Synthesis Example 23

Compound ID575

(163) ##STR00043##

(164) .sup.1H NMR (400 MHz, DMSO-d.sub.6): 7.35-7.55 (m, 8H), 7.15-7.45 (m, 4H), 6.85-7.10 (m, 26H), 6.75-6.85 (d, 4H), 6.50-6.60 (d, 2H), 3.76 (s, 6H), 3.74 (s, 12H)

Synthesis Example 24

Compound ID629

(165) ##STR00044##

(166) .sup.1H NMR (400 MHz, THF-d.sub.8): 7.50-7.56 (dd, 8H), 7.38-7.41 (dd, 4H), 7.12-7.16 (d, 8H), 7.02-7.04 (dd, 8H), 6.91-6.93 (d, 4H), 6.82-6.84 (dd, 8H), 6.65-6.68 (d, 4H) 3.87 (s, 6H), 3.74 (s, 12H)

Synthesis Example 25

Compound ID631

(167) ##STR00045##

(168) .sup.1H NMR (400 MHz, THF-de): 7.52 (d, 2H), 7.43-7.47 (dd, 2H), 7.34-7.38 (m, 8H), 7.12-7.14 (d, 2H), 6.99-7.03 (m, 12H), 6.81-6.92 (m, 20H), 3.74 (s, 18H), 2.10 (s, 6H)

(169) Spectroscopic Determination of the P-Doping of Spiro-MeOTAD in Solution

(170) Finally, studies were carried out as to what extent the above-described p-doping by metal oxides can be detected spectroscopically. For this purpose, 20 mg of spiro-MeOTAD were added to 628 mg of solvent (cyclohexanone), which corresponds to a concentration of 148 mM/l. The mixture was heated to 60 C. until complete dissolution and then cooled to room temperature. Subsequently, 30 l of a 0.3 molar LiTFSI solution in cyclohexanone were added. The particular dopant was added to this mixture in portions of 1 to 3 mg with shaking, until a more or less complete solution of the dopant in the particular mixture formed.

(171) The solutions prepared in this way were analyzed spectroscopically. One example of such a spectroscopic measurement is shown in FIG. 6. The absorbance E is plotted on the vertical axis, and the wavelength on the horizontal axis. The curve 152 denotes an absorbance measurement of a sample of the type described above, without addition of a metal oxide as a dopant. The curve 154 denotes an absorbance measurement on a sample in which 3 mg of rhenium oxide have been added according to the above method.

(172) As is discernible from FIG. 6, the sample with the metal oxide doping exhibits a distinct absorbance maximum at approximately 530 nm, in contrast to the undoped sample. It is accordingly possible, for example, to employ the absorbance of the mixtures comprising the oxidized hole conductors at 532 nm or at 1000 nm in a 1 mm cuvette as a quantitative measure of the p-doping of the hole conductor spiro-MeOTAD.

LIST OF REFERENCE NUMERALS

(173) 110 Photovoltaic element 112 Dye solar cell 114 Substrate 116 First electrode 118 Blocking layer 120 n-semiconductive material 122 Dye 124 Carrier element 126 p-semiconductor 128 Matrix material 130 Metal oxide 132 Second electrode 134 Layer structure 136 Encapsulation 138 Fermi level 140 HOMO 142 LUMO 144 Characteristic for comparative sample without metal oxide, t=0 146 Characteristic for comparative sample without metal oxide, t=2 days 148 Characteristic for example 1 sample, t=0 150 Characteristic for example 1 sample, t=2 days 152 Solution without rhenium oxide 154 Solution with rhenium oxide