ORGANOMETALLIC PEROVSKITE SOLAR CELL, TANDEM SOLAR CELL, AND MANUFACTURING PROCESS THEREFOR

Abstract

An organometallic perovskite solar cell and manufacturing process, in particular a solar cell having a lead or tin organometallic photon absorber layer. The organometallic solar cell includes an absorber layer containing a compound which crystallizes in the perovskite crystal lattice and which includes a lithium-free hole conductor layer.

Claims

1. A metal-organic solar cell comprising: at least two contact layers and, adjoining these, in each case a semiconducting layer in a layer stack having a centrally arranged absorber layer composed of a metal-organic material which crystallizes in the three-dimensional perovskite crystal lattice, where the absorber layer comprises lead as central atom and a halide as anion in a metal-organic compound, wherein the at least one semiconducting layer between the absorber layer and the anode is a hole-conducting layer which comprises a zinc-containing dopant.

2. A metal-organic solar cell comprising: at least two contact layers and, adjoining these, in each case a semiconducting layer in a layer stack having a centrally arranged absorber layer composed of a metal-organic material which crystallizes in the three-dimensional perovskite crystal lattice, where the absorber layer comprises tin as central atom and a halide as anion in a metal-organic compound, wherein the at least one semiconducting layer between the absorber layer and the anode is a hole-conducting layer which comprises a bismuth-containing dopant.

3. The solar cell as claimed in claim 1, wherein the zinc compound in the dopant is the salt of a superacid.

4. The solar cell as claimed in claim 1, wherein the solar cell comprises a diffusion barrier layer between the absorber layer and a semiconducting layer.

5. The solar cell as claimed in claim 4, wherein the diffusion barrier layer has a layer thickness of less than 150 nm.

6. The solar cell as claimed in claim 1, which in the matrix material of the hole conductor layer comprises one or more compounds selected from the group consisting of the following compounds: spiro-OMeTAD—2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spirobifluorene, PEDOT—poly(3,4-ethylenedioxythiophene), PVK—poly(9-vinylcarbazole), PTPD—poly(N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine), P3HT—poly(3-hexylthiophene), PANI—polyaniline, PTAA—poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], 9,9-bis [4-(N,N-bis-biphenyl-4-yl-amino)phenyl]-9H-fluorene, 4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine and/or ionic liquids, and also mixtures of the abovementioned compounds.

7. The solar cell as claimed in claim 1, wherein the absorber layer comprises a metal complex having tin and/or lead as central atom which contains at least one anion in the form of a halide or pseudohalide, selected from the group of the following elements: fluoride, chloride, bromide, iodide, cyanide, isocyanide.

8. The solar cell as claimed in claim 1, wherein the absorber layer comprises a metal complex having tin and/or lead as central atom to which a (CH.sub.3NH.sub.3).sup.+ ligand is coordinated.

9. A tandem solar cell comprising: at least two superposed solar cells in a layer stack, wherein one solar cell is a metal-organic solar cell as claimed in claim 1.

10. The tandem solar cell as claimed in claim 9, wherein the metal-organic solar cell is the upper solar cell on which the photons impinge first.

11. The tandem solar cell as claimed in claim 9, which comprises a solar cell having crystalline silicon in the absorber layer.

12. The tandem cell as claimed in claim 9, which comprises two metal-organic solar cells, wherein the two solar cells differ in terms of the composition of the material which forms the absorber layer.

13. A process for producing a layer body forming a tandem solar cell, comprising: producing a layer stack comprising two solar cells by layer deposition in a wet-chemical process, wherein a lower solar cell and an upper solar cell are produced by the production of sequential layers, wherein one of the solar cells is a metal-organic solar cell as claimed in claim 1.

14. The solar cell as claimed in claim 2, wherein the bismuth compound in the dopant is the salt of a superacid.

15. The solar cell as claimed in claim 2, wherein the solar cell comprises a diffusion barrier layer between the absorber layer and a semiconducting layer.

16. The solar cell as claimed in claim 15, wherein the diffusion barrier layer has a layer thickness of less than 150 nm.

17. The solar cell as claimed in claim 2, which in the matrix material of the hole conductor layer comprises one or more compounds selected from the group consisting of the following compounds: spiro—OMeTAD-2,2′,7,7′-tetrakis(N,N-di-p-methoxyphenylamine)-9,9′-spiro-bifluorene, PEDOT—poly(3,4-ethylenedioxythiophene), PVK—poly(9-vinylcarbazole), PTPD—poly(N,N-bis(4-butylphenyl)-N,N-bis(phenyl)benzidine), P3HT—poly(3-hexylthiophene), PANI—polyaniline, PTAA—poly[bis(4-phenyl)(2,4,6-trimethylphenyl)amine], 9,9-bis [4-(N,N-bis-biphenyl-4-yl-amino)phenyl]-9H-fluorene, 4,4′,4″-tris(N-(2-naphthyl)-N-phenyl-amino)triphenylamine and/or ionic liquids, and also mixtures of the abovementioned compounds.

18. The solar cell as claimed in claim 2, wherein the absorber layer comprises a metal complex having tin and/or lead as central atom which contains at least one anion in the form of a halide or pseudohalide, selected from the group of the following elements: fluoride, chloride, bromide, iodide, cyanide, isocyanide.

19. The solar cell as claimed in claim 2, wherein the absorber layer comprises a metal complex having tin and/or lead as central atom to which a (CH.sub.3NH.sub.3).sup.+ ligand is coordinated.

20. A tandem solar cell comprising at least two superposed solar cells in a layer stack, wherein one solar cell is a metal-organic solar cell as claimed in claim 2.

21. The tandem solar cell as claimed in claim 20, wherein the metal-organic solar cell is the upper solar cell on which the photons impinge first.

22. The tandem solar cell as claimed in claim 20, which comprises a solar cell having crystalline silicon in the absorber layer.

23. The tandem cell as claimed in claim 20, which comprises two metal-organic solar cells, wherein the two solar cells differ in terms of the composition of the material which forms the absorber layer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0084] FIG. 1 shows the structure of a metal-organic solar cell 1 in the n i p layout.

[0085] FIG. 2 shows the rise in the open circuit voltage of a metal-organic solar cell on changing from a lithium-doped hole conductor layer to a zinc-doped hole conductor layer.

[0086] FIG. 3 shows four different characteristic photovoltaic parameters.

[0087] FIG. 4 shows measurements on individual hole conductor layers without a solar cell structure.

[0088] FIG. 5 compares the stability of the hole conductor layers produced using zinc on the one hand and using lithium on the other hand.

DETAILED DESCRIPTION OF INVENTION

[0089] FIG. 1 shows the structure of a metal-organic solar cell 1 in the n-i-p layout, comprising at least the following layers: a transparent conductive electrode 7, for example an electrode composed of doped indium-tin oxide or another transparent conductive layer. This can have been applied to a support such as glass or be self-supporting.

[0090] On this layer, there is an n-conducting layer 2, for example composed of titanium dioxide. On top of this, there is the absorber layer, for example the layer 3 composed of CH.sub.3NH.sub.3PbI.sub.3 and/or CH.sub.3NH.sub.3SnI.sub.3 present in the three-dimensional perovskite structure. The absorber layer 3 can be planar or be present in the form of a framework structure here. Adjoining this layer, there is the hole transport layer 4 which in the present case is composed of a matrix material, for example the spiro-MeOTAD, with a dopant containing zinc and/or bismuth, in particular with Zn(TFSI).sub.2 and/or Bi(TFSI).sub.3, as is known from DE 10 2015 121844.

[0091] In the case of the dopant Zn(TFSI).sub.2 and/or Bi(TFSI).sub.3, a thin barrier layer, not shown here, is provided between the hole conductor layer 4 and the absorber layer 3 in an advantageous embodiment. This can be advantageous if the dopant has a tendency to diffuse into the absorber layer.

[0092] Instead of or together with the Zn(TFSI).sub.2, the following are, for example, also present as dopant: Bi(3,5-TFMBZ).sub.3, bismuth(III) tris(3,5-bistrifluoromethyl)benzoate, Bi(4-pFbz).sub.3, bismuth(III) tris(4-pentafluoro)benzoate, K(TFSI), K(I) bis(trifluoromethanesulfonyl)imide and/or Zn(II) bis(trifluoromethanesulfonyl)imide and/or sodium(I) bis(trifluoromethane-sulfonyl)imide.

[0093] Furthermore, trifluoromethanesulfonates such as Zn(TFMS).sub.2 can also advantageously be used as dopant. As an alternative or in addition, it is also possible to utilize “ionic liquids” as effective dopants.

[0094] Finally, the counterelectrode, for example composed of aluminum, silver and/or gold, is additionally present on the hole conductor layer 4.

[0095] The total structure is advantageously protected against moisture and/or air by an encapsulation 6.

[0096] FIG. 2 shows the rise in the open circuit voltage of a metal-organic solar cell on changing from a lithium-doped hole conductor layer to a zinc-doped hole conductor layer.

[0097] FIG. 3 shows four different characteristic photovoltaic parameters (JSC (short circuit current), VOC (open circuit voltage), FF (fill factor) and PCE (photocurrent efficiency)) of perovskite solar cells, here as a comparison between a perovskite solar cell having spiro-MeOTAD/LiTFSI (black) and spiro-MeOTAD/Zn(TFSI).sub.2 (red) as hole conductor layer.

[0098] These measurements in each case compare the metal-organic solar cells with lithium-doped and zinc-doped hole conductor layers with an otherwise identical structure and under the same measurement conditions. Thus, these measurements clearly show that the solar cells constructed with a zinc-doped hole conductor layer are at least equal to the conventional lithium-doped solar cells. This is all the more astonishing since the doping concentration decreases significantly from lithium to zinc and/or bismuth, which brings about a significant economic advantage.

[0099] FIG. 4 shows measurements on individual hole conductor layers without a solar cell structure. The current density at various doping concentrations at various voltages can be seen in the figure, with the result that above 0.2 mol of dopant per mole of matrix compound, it is obviously no longer possible to achieve any significant increase in the current density by increasing the doping concentration.

[0100] FIG. 4 shows not only the current-voltage curves, which can be seen at left, but also, at right, the corresponding photovoltaic parameters such as JSC, VOC, FF and PCE as a function of the concentration of the dopant Zn(TFSI).sub.2 in the matrix material spiro-MeOTAD.

[0101] It is conspicuous here that, in particular, the “fill factor” was improved significantly. The fill factor refers to the quotient of the maximum power of a solar cell at the maximum power point and the product of open circuit voltage and short circuit current.

[0102] Overall, it can be concluded from the measurements that the metal-organic solar cells which are built up with a hole conductor layer having the zinc- and/or bismuth-based dopant according to the invention and have an absorber layer composed of a material which crystallizes in the three-dimensional perovskite structure display very good efficiency of the light-into-electricity conversion.

[0103] Finally, the stability of the hole conductor layers produced using zinc on the one hand and using lithium on the other hand is compared in FIG. 5. It can be seen that the conventional lithium-doped hole conductor layers are far less stable than the corresponding hole conductor layers containing zinc and/or bismuth. This is related, inter alia, to the fact that the small lithium ion naturally diffuses more easily and quickly in the case of a temperature increase and/or in an electric field and thus decreases the homogeneity of the hole conductor layers. In the case of the PCE (power conversion efficiency)/PCE measurement, in particular, it can be clearly seen how the efficiency of the lithium-doped hole conductor layer decreases with increasing number of hours.

[0104] The present invention for the first time discloses a metal-organic solar cell comprising an absorber layer containing a compound which crystallizes in the perovskite crystal lattice and having a low-lithium hole conductor layer.