PEDOT IN PEROVSKITE SOLAR CELLS

Abstract

The present invention relates to a process for the production of a layered body (1), at least comprising the process steps: I) provision of a photoactive layer comprising a material having a perovskite type crystal structure; II) superimposing the photoactive layer at least partially with a coating composition A) comprising an electrically conductive polymer a) and an organic solvent b); III) at least partial removal of the organic solvent b) from the coating composition A) superimposed in process step II), thereby obtaining an electrically conductive layer superimposed on the photoactive layer. The present invention also relates to a layered body obtainable by this process, to dispersions, to an electronic device, to a process for the preparation of a photovoltaic device and to the photovoltaic device that is obtainable by this process.

Claims

1. A process for the production of a layered body, comprising the process steps: I) providing a photoactive layer comprising a material having a perovskite type crystal structure; II) partially superimposing the photoactive layer with a coating composition A) comprising an electrically conductive polymer and b) an organic solvent; and III) partially removing the organic solvent b) from the coating composition A) superimposed in process step II), thereby obtaining an electrically conductive layer superimposed on the photoactive layer.

2. The process according to claim 1, wherein the material having a perovskite type crystal structure has the formula R′MX.sub.3, wherein R′ is an organic, monovalent cation selected from primary, secondary, tertiary and quaternary organic ammonium compounds, R′ having from 1 to 15 carbons and 1 to 20 heteroatoms, or R′ is Cs.sup.+; M is a divalent metal cation selected from the group consisting of Cu.sup.2+, Ni.sup.2+, Co.sup.2+, Fe.sup.2+, Mn.sup.2+, Cr.sub.2+, Pd.sup.2+, Cd.sup.2+, Ge.sup.2+, Sn.sup.2+, Pb.sup.2+, Eu.sup.2+ and Yb.sup.2+; and each X is independently selected from the group consisting of F.sup.−, Cl.sup.−, Br.sup.−, I.sup.−, NCS.sup.−, CN.sup.− and NCO.sup.−.

3. The process according to claim 2, wherein R′ is CH.sub.3NH.sub.3.sup.+, M is Pb.sup.2+, and each X is independently selected from the group consisting of F.sup.−, Cl.sup.−, I.sup.− and Br.sup.−.

4. The process according to claim 1, wherein the conducting polymer a) comprises cationic polythiophene.

5. The process according to claim 4, wherein the conducting polymer a) is a salt or a complex of a cationic polythiophene and a counter-ion.

6. The process according to claim 5, wherein the counter-ion is a copolymer comprising polymerized styrene monomer units at least a part of which is sulfonated and polymerized non-sulfonated monomer units and wherein the molar ratio of the non-sulfonated monomer units is at least 5%, based on the total amount of monomer units in the copolymer.

7. The process according to claim 5, wherein the counter-ion is a hydrogenated styrene-isoprene block copolymer with the structure A-B-C-B-A, in which block A is a polystyrene block which is at least partially substituted with tert-butyl groups, block B is a block of alternating copolymerized ethylene-propylene units and block C is a sulphonated polystyrene block.

8. The process according to claim 1, wherein the water content of coating composition A) is less than 2 wt.-%, based on the total weight of coating composition A).

9. The process according to claim 1, wherein the organic solvent b) is a non-polar, aprotic solvent.

10. The process according to claim 1, wherein the dielectric constant of the organic solvent b) is between 1×10.sup.−30 and 20×10.sup.−30 Cm.

11. The process according to claim 1, wherein the organic solvent b) has a dipole moment of less than 7 D.

12. The process according to claim 1, wherein the organic solvent b) is a solvent that, when being superimposed on the surface of the photoactive layer, exhibits a ΔA-value of less than 5%, wherein the ΔA-value is calculated by formula (I)
ΔA=(A.sub.0−A.sub.D)/A.sub.0×100%  (I) wherein A.sub.0 is the absorption of the photoactive layer before and A.sub.D the absorption of the photoactive layer after the photoactive layer has been superimposed with the organic solvent b) for 30 s, in each case determined at 490 nm.

13. The process according to claim 1, wherein the photoactive layer is at least partially covered with one or two additional layers before it is superimposed with coating composition A) in process step II).

14. A layered body obtainable by the process according to claim 1.

15. A dispersion comprising: a) a salt or a complex of a cationic polythiophene with a counter-ion; b) an organic solvent with a ΔA-value of less than 5%, wherein the ΔA-value is calculated by formula (I)
ΔA=(A.sub.0−A.sub.D)/A.sub.0×100%  (I) wherein A.sub.0 is the absorption before and A.sub.D the absorption after a CH.sub.3NH.sub.3PbI.sub.3-layer has been superimposed with the organic solvent b) for 30 s, in each case determined at 490 nm.

16. A dispersion comprising: a) a salt or a complex of a cationic polythiophene with a counter-ion; b) an organic solvent with a dielectric constant between 1×10.sup.−30 and 20×10.sup.−30 Cm; c) an additive selected from a metal nanowire, a carbon nanotube, a graphene and a crosslinking agent.

17. A dispersion comprising: a) a salt or a complex of a cationic polythiophene with a counter-ion; b) an organic solvent; wherein the dispersion has an iron content of less than 100 ppm, based on the total weight of the dispersion.

18. The dispersion according to claim 15, wherein the polymeric counter ion is a copolymer comprising polymerized styrene monomer units at least a part of which is sulfonated and polymerized non-sulfonated monomer units and wherein the molar ratio of the non-sulfonated monomer units is at least 5%, based on the total amount of monomer units in the copolymer.

19. The dispersion according to claim 15, wherein the counter-ion is a hydrogenated styrene-isoprene block copolymer with the structure A-B-C-B-A, in which block A is a polystyrene block which is at least partially substituted with tert-butyl groups, block B is a block of alternating copolymerised ethylen-propylene units and block C is a sulphonated polystyrene block.

20. The dispersion according to claim 15, wherein the conductivity of an electrically conductive layer made by coating a glass substrate with the dispersion and drying the thus obtained layer structure for 3 minutes at 200° C. on a hot plate is at least 0.2 S/cm.

21. The dispersion according to claim 15, wherein the water content of the dispersion is less than 2 wt. %, based on the total weight of the dispersion.

22. An electronic device comprising a layered body according to claim 14.

23. The electronic device according to claim 22, wherein the electronic device is a photovoltaic device.

24. A process for the preparation of a photovoltaic device, comprising the process steps: i) providing a multilayer-precursor body comprising a first electrode; a photoactive layer, wherein the photoactive layer is made of a material having a perovskite type crystal structure; and an electron transport layer that is localized between the first electrode and the photoactive layer; ii) partially superimposing the photoactive layer of the multilayer-precursor body with a coating composition A) comprising an electrically conductive polymer and b) an organic solvent; iii) partially removing the organic solvent b) from the coating composition A) superimposed in process step ii), thereby obtaining an electrically conductive hole transport layer superimposed on the photoactive layer; and iv) partially superimposing the hole transport layer with a second electrode.

25. A photovoltaic device obtained by the process according to claim 24.

26. An electronic device comprising an electrically conductive layer, wherein the electrically conductive layer comprises a dispersion according to claim 15.

Description

[0170] FIG. 1 shows a schematic representation of the sequence of layers according to the invention obtainable by a process for the preparation of a photovoltaic device 1, the photovoltaic device 1 being a solar cell with an inverted structure. It comprises a glass substrate 2 on which a transparent first electrode 3 serving as the cathode layer is applied from, for example, ITO. The first electrode 3 is followed by an electron transport layer 4 for the improvement of electron extraction, such as a TiO.sub.x layer. Onto the electron transport layer 4 is applied a photoactive layer 5 made of a material having a perovskite type crystal structure, for example CH.sub.3NH.sub.3PbI.sub.3. Onto the photoactive layer 5 there is applied a conductive polymer layer serving as a hole transport layer 6 that is preferably based on a salt or complex of a polythiophene and a counter-ion. Onto the conductive polymer layer 6 there is applied a non-transparent second electrode 7 serving as the anode layer, such as a silver layer. In this particular embodiment of a solar cell with an inverted structure light reaches the photoactive layer from beneath through the glass substrate and the transparent first electrode 3 (indicated by the arrows in FIG. 1). The dotted circle FIG. 1 indicates a layered structure according to the present invention.

[0171] FIG. 2 shows a schematic representation of the sequence of layers of the photovoltaic device shown in FIG. 1, with the difference that the first electrode 3 is made of a non-transparent material, such as an aluminium layer, and the second electrode 7 is a transparent layer, for example a metal layer that is applied in the form of parallel strips or in the form of a grid or that is based on a conductive polymer, such as PEDOT. In this particular embodiment of a solar cell with an inverted structure light reaches the photoactive layer from above through the second electrode 7 and the transparent layer of the conductive polymer 6 (indicated by the arrows in FIG. 2). The dotted circle FIG. 2 again indicates a layered structure according to the present invention.

[0172] FIG. 3 shows a schematic representation of the sequence of layers of the photovoltaic device shown in FIG. 1, with the difference that the second electrode 7 is also a transparent layer. In this particular embodiment of a solar cell with an inverted structure light reaches the photoactive layer from beneath through the glass substrate and the transparent first electrode 3 and from above through the second electrode 7 and the transparent layer of the conductive polymer 6 (indicated by the arrows in FIG. 3). The dotted circle FIG. 3 again indicates a layered structure according to the present invention.

TEST METHODS

[0173] To evaluate the functional behaviour of a layer of the composition employed in the process according to the invention to the photoactive layer, the procedure is as follows:

[0174] Substrate Cleaning

[0175] ITO-precoated glass substrates (5 cm×5 cm) are cleaned by the following process before use: [0176] 1. thorough rinsing with acetone, isopropanol and water, [0177] 2. ultrasound treatment in a bath at 70° C. in a 0.3% strength Mucasol solution (Merz) for 15 min, [0178] 3. thorough rinsing with water, [0179] 4. drying by spinning off in a centrifuge, [0180] 5. UV/ozone treatment (PR-100, UVP Inc., Cambridge, GB) for 15 min directly before use.

[0181] TiO.sub.x planar layer (according to literature: Docampo et al. Nature Comm. 2013)

[0182] The titanium sub-oxide (TiO.sub.x) planar layer is solution-processed. The process comprises the application of four solutions: [0183] a) Hydrochloric acid (HCl) stock solution 1: [0184] 0.5 g concentrated HCl (37 wt. %, technical grade, AppliChem) are added to 1.55 g of isopropanol (anhydrous, 99.5%, Sigma-Aldrich) and stirred for 15 min in air leading to a 2M HCl stock solution. [0185] b) HCl stock solution 2: [0186] 600 μL of HCl stock solution 1 are diluted in 34.5 g of isopropanol (anhydrous, 99.5%, Sigma-Aldrich) and stirred for ca. 12 h under nitrogen leading to a 0.026 M HCl stock solution. [0187] c) TiO.sub.x precursor solution 1: [0188] 554 μL titanium(IV) isopropoxide (99.99%, trace metal basis, Sigma-Aldrich) is added to 3.00 g of isopropanol using a micropipette followed by 15 minutes of stirring. All handling is done under nitrogen in a glovebox. [0189] d) TiO.sub.x precursor solution 2: [0190] 3.00 g of HCl stock solution 2 are added slowly by dropping to 3.00 g of TiO.sub.x precursor solution 1 under vigorous stirring. The solution was stirred for 15 min before filtering through a 0.45 μm PTFE syringe filter. The solution should be used fresh.

[0191] The solution is then applied to the cleaned ITO substrate by spin coating at 2000 rpm for 60 seconds and then dried in air on a hot-plate at 300° C. for 30 min. before drying the edges are cleaned of the TiO.sub.x to allow good contact for the device fabricated later on. This heat treatment of ITO did not compromise its initial conductivity

[0192] Active layer (according Jeng et al. Adv. Mat. 2013)

[0193] Perovskite Precursor Solution:

[0194] 0.56 g lead(II) iodide (PbI.sub.2, 99%, Sigma-Aldrich) and 0.19 g methyl ammonium iodide (CH.sub.3NH.sub.3I, Solaronix) are dissolved in 2.5 g of N,N-dimethyl formamid (DMF, anhydrous, 99.8%, Sigma-Aldrich) in 1:1 equimolar ratio (30 wt. %) in a screw cap pill bottle and stirred at 60° C. for 12 hours or until all the material has dissolved. All handling and processing is done under nitrogen in a glovebox.

[0195] Perovskite Photo-Active Layer Device Preparation:

[0196] The perovskite precursor solution is now dripped on to the ITO/TiO.sub.x substrate and superfluous solution is spun off by spin coating at 3000 rpm for 30 seconds using a spin acceleration of 200 rpm/s. During the coating process and especially during drying step at elevated temperature the deep purple light absorbing perovskite CH.sub.3NH.sub.3PbI.sub.3 is formed. The layers are then dried directly on a hot-plate at 100° C. for 15 min followed by 2 min at 130° C. in air.

[0197] Deposition of the Conductive PEDOT:Counterion Layer

[0198] For the production of the PEDOT:counter-ion layer (hole transport layer) the dispersion is applied onto the above mentioned photoactive layer (layer sequence glass substrate/ITO/TiO.sub.x/CH.sub.3NH.sub.3PbI.sub.3 as a precursor (cf. sample preparation)). The coating composition was applied onto the CH.sub.3NH.sub.3PbI.sub.3-layer of the precursor by means of a pipette to completely cover the area. Excess dispersion was spun off by spin coating (conditions: 20 s at approx. 1,000 rpm, in air). Thereafter, a drying process on a hot-plate was carried out in two steps: 5 min at 80° C. in air, followed by 10 min at 130° C. under nitrogen.

[0199] OPV Cells

[0200] For the further test of the coating composition, OPV cells having the following inverted layer structure of glass substrate/ITO/TiO.sub.x/CH.sub.3NH.sub.3PbI.sub.3/conductive PEDOT:counterion layer/silver were produced, TiO.sub.x having been applied with a layer thickness of approx. 70 nm, CH.sub.3NH.sub.3PbI.sub.3 with a layer thickness of approx. 200-250 nm and PEDOT:counterion of about 100 nm, in the given sequence in accordance with the instructions already described above. The silver electrodes having a layer thickness of 300 nm were vapour-deposited using a reduced pressure vapour deposition unit (Edwards) at <5×10.sup.−6 mbar through shadow masks with a vapour deposition rate of about 10 Å/s. The shadow masks define the photoactive area of 0.28 cm.sup.2. For accurate photocurrent measurement, the individual cells were carefully scratched out with a scalpel and therefore reduced to the precisely defined area, in order to avoid edge effects with additionally collected current due to conductive PEDOT:counterion or CH.sub.3NH.sub.3PbI.sub.3. For measurements a pixel mask was applied to define the precise active area of measurement. Further all layers were removed at the substrate edges and painted with liquid silver paint to allow a good contact to ITO for device measurements. Now the devices were ready for current-voltage measurements and photovoltaic performance characterisation.

[0201] Superficial Dissolving Properties

[0202] The superficial dissolution of the photoactive layer (such as a CH3NH3PbI3-layer) is checked by the following process: [0203] a) a stationary film of organic solvent b) is applied onto the photoactive layer for 30 s, wherein the photoactive layer has a thickness in the range from 100-300 nm (the film of liquid was applied over a large area on the active layer with a pipette); [0204] b) the stationary film is washed off with toluene; [0205] c) the washed film is rotated at 2000 rpm for 30 s; [0206] d) the rotated film is dried on a hot plate for 1 min at 80° C.

[0207] If superficial dissolving takes place during the covering, this leads to a visible change in the colour or intensity of the contact area of the film. The superficial dissolving effect by the composition was measured by UV/Vis spectroscopy (PerkinElmer Lambda 900). In this context, the absorption of the non-treated active layer was measured and compared at exactly the same place before application of the liquid film and after washing off and drying. For the comparison, a wavelength of 490 nm was chosen. The change in the absorption at a wavelength then expresses the reduction in absorption and the associated detachment of material. If the liquid film does not lead to any superficial dissolving the surface remains unchanged, if dissolving is complete the film is removed from the contact area. The change in absorption at 490 nm ΔA was calculated according to the following formula:

ΔA=(A.sub.0−A.sub.D)/A.sub.0×100%

wherein A.sub.0 is the absorption before the dissolution and A.sub.D after the dissolution. When determining the A.sub.0- and A.sub.D-value the absorption of the substrate onto which the photoactive layer is applied has to be subtracted (A.sub.0=A.sub.0, as determined−A.sub.Substrate; A.sub.D=A.sub.D, as determined−A.sub.substrate).

[0208] Cell Characterization

[0209] The perovskite PV cells produced were measured with a solar simulator (1,000 W quartz-halogen-tungsten lamp, Atlas Solar Celltest 575) with a spectrum of 1.5 AM. The light intensity can be attenuated with inserted grating filters. The intensity at the sample plane is measured with a Si photocell and is approx. 1,000 W/m.sup.2. The Si photocell was calibrated beforehand with a pyranometer (CM10). The temperature of the sample holder is determined with a heat sensor (PT100+testtherm 9010) and is max. 40° C. during the measurement. The two contacts of the OPV cell are connected to a current/voltage source (Keithley 2800) via a cable. Before measuring, the cell was light soaked for 5 minutes to activate the TiO.sub.x to allow full functionality and reproducibility. For the measurement, the cell was scanned in the voltage range of from −1.0 V to 1.5 V and back to −1.0 V and the photocurrent was measured. The measurement steps were 0.01 V every 5 seconds to allow full charge equilibrium and to avoid hysteresis effect s. The measurement was performed three times per cell in total, first in the dark, then under illumination and finally in the dark again, in order to guarantee complete functioning of the cell after illumination. The data were recorded via a computer-based Labview program. This leads to the typical current density/voltage characteristic line of a diode, from which the OPV characteristic data, such as “open circuit voltage” (V.sub.oc), “short circuit current density” (J.sub.sc), fill factor (FF) and efficiency or effectiveness (Eff.) can be determined either directly or by calculation in accordance with the European standard EN 60904-3. The fill factor is then calculated according to Equation 1:

[00001]$\begin{array}{cc}\mathrm{FF}=\frac{V_{\mathrm{mpp}}.Math.J_{\mathrm{mpp}}}{V_{\mathrm{OC}}.Math.J_{\mathrm{SC}}}& \mathrm{Equation}.Math..Math.1\end{array}$

wherein V.sub.mpp is the voltage and J.sub.mpp the current density at the “maximum power point” (mmp) on the characteristic line of the cell under illumination.

[0210] Electrical Conductivity:

[0211] The electrical conductivity means the inverse of the specific resistance. The specific resistance is calculated from the product of surface resistance and layer thickness of the conductive polymer layer. The surface resistance is determined for conductive polymers in accordance with DIN EN ISO 3915. In concrete terms, the polymer to be investigated is applied as a homogeneous film by means of a spin coater to a glass substrate 50 mm×50 mm in size thoroughly cleaned by the abovementioned substrate cleaning process. In this procedure, the coating composition is applied to the substrate by means of a pipette to completely cover the area and spun off directly by spin coating. The spin conditions for coating compositions were 20 s at approx. 1,000 rpm in air. Thereafter, a drying process on a hot-plate was carried out (3 min at 200° C. in air). For the test of the examples 6 and 7 (comparative examples) the drying process on a hot-plate was carried out 15 min at 130° C. in air. In all cases silver electrodes of 2.0 cm length at a distance of 2.0 cm are vapour-deposited on to the polymer layer via a shadow mask. The square region of the layer between the electrodes is then separated electrically from the remainder of the layer by scratching two lines with a scalpel. The surface resistance is measured between the Ag electrodes with the aid of an ohmmeter (Keithley 614). The thickness of the polymer layer is determined with the aid of a Stylus Profilometer (Dektac 150, Veeco) at the places scratched away.

[0212] Solids Content:

[0213] The solid content was determined by gravimetry using a precision scale (Mettler AE 240). First the empty weighing bottle including lid is weight in (Weight A). Then ca. 3 g of dispersion to be analysed is filled quickly into the bottle, closed by the lid and weighed again to determine the exact total weight B. The bottle is then placed in a fume hood without a lit for ca. 3 hours to allow the evaporation of volatile solvents at room temperature. In a second step the bottle is placed in a drying oven with ventilation (Memmert UNB200) at 100° C. for 16 17 hours. When the sample bottle is removed from the oven, immediate coverage by the glass lid is important due to the hygroscopic nature of the dry dispersion material. After 10-15 min of cooling down period the bottle is weighed again including lid to determine weight C. There is always a repeat determination of 2 samples.

wt.% solids content=100×(C−A)/(B−A)  Calculation of the solid contents:

[0214] Water Content Measurement by Karl-Fischer Titration:

[0215] The water content is determined by Karl Fischer titration. A Metrohm 787 KF Titrino with a 703 titration stand is used to this end. The titration vessel is filled with analytical-grade methanol so that about 1 cm of the platinum electrode is submerged. Then approximately 5 ml of Hydranal buffer acid is pipetted in. The titration cell is automatically dried by starting the KFT program. Preparation is complete when the message “KFT conditioned” appears. Approximately 5 ml of the dispersion to be analysed is then introduced into the titration vessel using a syringe and the exact mass of the dispersion used is determined by back-weighing the syringe. The titration is then started. The measured value is determined as the mean of three individual measurements.

[0216] Iron Content:

[0217] The iron content was determined by inductively coupled plasma optical emission spectrometry (ICP-OES) using ICP-OES Spectroblue that was equipped with Autosamples Cetac ASX-520 and Smart-Analyser-Vision software.

Example 1

[0218] In a 1 L three-necked round-bottom flask equipped with mechanical stirrer 7.9 g of 3,4-ethylenedioxythiophene (Heraeus Precious Metals GmbH & Co KG, Germany) were added to a mixture of 130 g of tert-butyl methyl ether, 215 g of a solution of sulfonated block-copolymer in cyclohexane/heptane-mixture (Kraton Nexar MD 9150, 11.0% solids) and 9 g of para-toluene sulfonic acid (Aldrich) and stirred for 30 min. 15 g of dibenzoylperoxide (Aldrich) were added and the mixture was heated to reflux. After 6 h the mixture was allowed to cool to room temperature and diluted with 1175 g of tert-butyl methyl ether. After two days residual solids were filtered off and the filtrate was purified by diafiltration (ceramic membrane filter (Pall Schumasiv, pore size 50 nm, part number 88519721) in order to remove low molecular weight impurities <50 nm. After purification the solids content was determined to be 2.1%.

[0219] Analysis

TABLE-US-00001 Solids content: 2.1% (gravimetric) Water content: 0.2% (Karl-Fischer-Titration) Solvent composition: 88% methyl tert-butyl ether, 6% cyclohexane, 6% n-heptane; Ratio PEDOT:counter-ion: 1:3 (w/w) Iron content: less than 10 ppm

Example 2

[0220] A 3 L three-necked round-bottom flask equipped with mechanical stirrer was charged with 1233 g toluene (Aldrich), 19.1 g of dipenzoylperoxide (158 mmol; Aldrich), 282 g of a solution of sulfonated block-copolymer in cyclohexane/heptane-mixture (Kraton Nexar MD 9150, 11.0% solids) and 46 g of para-toluene sulfonic acid (240 mmol, Aldrich). While stirring the mixture was purged with nitrogen gas for 30 min. After heating to 60° C. 10 g of 3,4-ethylenedioxythiophene (70 mmol; Clevios M V2; Heraeus Precious Metals GmbH & Co KG, Germany) dissolved in 137 g of toluene were added dropwise over 1 h. The dispersion was stirred for another 4 h at 60° C. After cooling to room temperature the dispersion was let to stand for one week before removing solids by filtration.

[0221] Analysis:

TABLE-US-00002 Solids content: 2.6% (gravimetric) Residual Water: 0.1% (Karl-Fischer-Titration) Conductivity: 0.2 S/cm Solvent composition: 86% toluene, 7% cyclohexane, 7% n-heptane Ration PEDOT:counter-ion: 1:3 Iron content: less than 10 ppm

Example 3

[0222] The polymerization was prepared analog to Example 2 except that heptane was used as solvent.

[0223] Analysis:

TABLE-US-00003 Solids content: 2.6% (gravimetric) Residual Water: 0.2% (Karl-Fischer-Titration) Conductivity: 0.2 S/cm Iron content: less than 10 ppm

Example 4

[0224] The polymerization was prepared analog to Example 2 except that a mixture of methyl-tert-butylether and ethylacetate (50:50 w/w) was used as solvent.

[0225] Analysis:

TABLE-US-00004 Solids content: 2.6% (gravimetric) Residual Water: 0.2% (Karl-Fischer-Titration) Conductivity: 2.0 S/cm Iron content: less than 10 ppm

Comparative Example 1

[0226] A PEDOT:PSS dispersion was prepared in accordance with Example 2 of DE 10 2007 041722 A1.

[0227] Analysis:

TABLE-US-00005 Solid content: 1.3% (gravimetric) Water content: 98.7% Conductivity: 0.1 S/cm (without dimethylsulfoxide) Ratio PEDOT:PSS 1:2.5 Iron content: less than 10 ppm

Comparative Example 2

[0228] The dispersion was prepared in accordance with composition 1a of WO 2014/154360 A2.

[0229] Analysis:

TABLE-US-00006 Solid content: 0.7% (gravimetric) Water content: 6% water Conductivity: 100 S/cm Ratio PEDOT:PSS 1:2.66 Solvents: water; ethylene glycol; propylene glycol; ethanol; isopropanol; dichlorobenzene Iron content: less than 10 ppm

TABLE-US-00007 TABLE 1 List of all the coating compositions according to the invention and comparative examples with the solvent type or system, content of water and solids and conductivity. solids water Coating content content conductivity composition main solvent wt. % wt. % S cm.sup.−1 Example 2 toluene 2.6 0.1 0.2 (inventive) Example 3 heptane 2.6 0.2 0.2 (inventive) Example 4 MTBE:EA (1:1) 2.8 0.2 2.0 (inventive) Comparative water 1.3 98.7 0.1 Example 1 Comparative propylene glycol/EG 0.7 6 100 Example 2

Example 5

[0230] This example comprises experiments for further characterization and coating properties of solvent based PEDOT dispersions.

[0231] In the investigation of the superficial dissolving properties, for possible solvents as part of the coating composition according to the invention no superficial dissolving of the CH.sub.3NH.sub.3PbI.sub.3 layer (490 nm) was found after 30 s of solvent exposure (see table 2). A reduction in the absorption of >5% was evaluated as a superficial dissolving process. In case of >50% a clear change in colour and intensity was to be found even with the naked eye which showed the complete removal of the layer, which thus clearly lies above a 50% reduction in absorption. Water, ethylene glycol, diethylene glycol and isopropanol (any polar alcohols) dissolve the active layer completely. Coating compositions based on non-polar organic solvents, on the other hand, showed no superficial dissolving properties.

TABLE-US-00008 TABLE 2 Superficial dissolving properties of selected solvents compared for CH.sub.3NH.sub.3PbI.sub.3 after an action time of 30 s by a reduction in the absorption at the characteristic wavelengths of 490 nm as well as the dipole moment and the dielectric constant of the selected solvents. Dipole moment Dielectric constant ΔA of solvent of solvent Batch/coating composition [%] [D] [×10.sup.−30 Cm] Water >95 1.85 D 80 Isopropanol >95 1.66 D 18 Isobutanol 22 1.79 D 16.68 1-Octanol 8 1.68 D 10.30 Ethylene glycole >95 2.28 D 39 Diethylene glycol >95 2.69 D 31.70 Propylene glycole 64 2.27 D 32 Tetrahydrofurane >95 1.63 D 7.5 Toluene 3 0.36 D 2.38 Heptane 5 0.35 D 1.92 Butylbenzoate 4 1.54 D 5.52 Ethylacetate 10 1.78 D 6.02 Methyl-tert-butylether 3  1.4 D 2.6 (MTBE) Hexamethyldisiloxane <2  0.8 D 2.2 Polysiloxane <2 0.6-0.9 D .sup.  <3 Anisole 2 1.38 D 4.33 Xylene 2 0.07 D 2.2 Dichlorobenzene 2 2.14 D 9.8 Tetraline 2 0.61 D 2.77

[0232] Table 3 shows that coating compositions according to the present invention all demonstrate a better film formation on top of the active layer CH.sub.3NH.sub.3PbI.sub.3 than the coating compositions of the comparative examples. A very good wetting, was observed which indicates a good compatibility with the underlying active layer.

TABLE-US-00009 TABLE 3 Film formation by the conductive polymer coating composition. Coating composition Composition solvent film formation Example 2 Toluene ++ Example 3 Heptane ++ Example 4 MTBE:EA (1:1) ++ Comparative Example 1 Water −− Comparative Example 2 propylene glycol/EG −−

[0233] ++=defect-free, homogeneous layer; +=homogeneous layer with <30 area % hole defects in the layer; 0=homogeneous layer with more than 30 to 60 area % hole defects in the layer; −=more than 60 area % hole defects in the layer; −−=no layer formation/beading

Example 6

[0234] Example 6 shows the device performance of a Perovskite type solar cell using the dispersion prepared in Example 2 in comparison to the dispersions prepared I Comparative Examples 1 and 2.

[0235] For the test of the comparative examples based on either aqueous dispersion of Comparative Example 1 or the solvent based dispersion of Comparative Example 2 in the same layer sequence of glass substrate/ITO/TiO.sub.x/CH.sub.3NH.sub.3PbI.sub.3 as the precursor, the conductive polymer layer was in turn formed on the CH.sub.3NH.sub.3PbI.sub.3-layer. The dispersions were applied to the CH.sub.3NH.sub.3PbI.sub.3-layer of the precursor by means of a pipette to completely cover the area and were immediately spun off by spin coating (conditions: 30 s at approx. 1500 rpm, in air). Thereafter, the drying process on a hot-plate was carried out in two steps: 5 min at 80° C. in air, followed by 10 min at 130° C. under nitrogen.

TABLE-US-00010 TABLE 4 Photovoltaic device characteristic data of cells with coating composition as obtained in Example 2 from toluene according to the invention in cell a) and reference materials as comparative examples with coating composition based on the aqueous dispersion of Comparative Example 1 in cell b) or with coating composition based on the dispersion of Comparative Example 2 in cell c). PEDOT:counter- Active OPV ion type coating area V.sub.OC J.sub.SC Eff. cell composition [cm.sup.2] [V] [mA .Math. cm.sup.−2] FF [%] Cell a) Example 2 0.28 0.41 7.08 0.40 1.15 Cell b) Comparative 0.28 0 0 0 0.00 Example 1 Cell c) Comparative 0.28 0 0 0 0.00 Example 2

[0236] Working perovskite PV cells could be produced from Example 2 according to the invention. With a J.sub.SC of 7.10 mA cm.sup.−2, a FF of 0.45 and an efficiency >0% the device works according to the definition of a photovoltaic cell. A Jsc >0 mA.Math.cm.sup.−2 shows a photo response and generated current from incoming light. Coating composition reference materials obtained in Comparative Examples 1 and 2 were not suitable for the production of a perovskite PV cell due to incompatibility of the solvent systems with the active material perovskite by means of complete dissolution.