Solar cells with a barrier layer based on polysilazane

1. A process for producing a chalcopyrite solar cell, comprising the steps of:

a) coating a substrate composed of metal, metal alloys, glass ceramic or plastic with a solution comprising at least one polysilazane of the formula (I)

—(SiR′R″—NR′″) n -  (I)

where R′, R″, R′″ are the same or different and are hydrogen or an optionally substituted alkyl, aryl, vinyl or (trialkoxysilyl)alkyl radical, where n is an integer and is such that the at least one polysilazane has a number-average molecular weight of 150 to 150,000 g/mol,

b) removing the solvent by evaporation to obtain a polysilazane layer having a thickness of 100 to 3000 nm, on the substrate,

c) optionally repeating steps a) and b) once or more than once

d) hardening the polysilazane layer by i) heating to a temperature in the range from 20 to 1000° C., ii) irradiating with UV light having wavelength components in the range from 10 to 230 nm or both, the heating irradiation or both is effected over a period of 1 min to 14 h,

e) further hardening the polysilazane layer at a temperature of 20 to 1000° C., in air having a relative humidity of 60 to 90% over a period of 1 min to 2 h,

f) applying a photovoltaic layer structure based on chalcopyrite, and

g) applying an encapsulation layer to the photovoltaic layer structure according to steps a) to e).

2. The process as claimed in claim 1 , wherein the polysilazane solution comprises at least one perhydropolysilazane where R′, R″ and R′″=H.

3. The process as claimed in claim 1 , wherein the polysilazane solution comprises a catalyst, and optionally further additives.

4. The process as claimed in claim 1 , wherein the polysilazane solution contains sodium.

5. The process as claimed in claim 1 , wherein step d) or e) is followed by deposition of a sodium-containing precursor layer on the polysilazane layer.

6. The process as claimed in claim 1 , wherein the chalcopyrite solar cell is manufactured on a flexible weblike substrate in a roll-to-roll process.

7. The process as claimed in claim 1 , wherein the at least one polysilazane has a number-average molecular weight of 50,000 to 150,000 g/mol.

8. The process as claimed in claim 1 , wherein the at least one polysilazane has a number-average molecular weight of 100,000 to 150,000 g/mol.

9. The process as claimed in claim 1 , wherein the polysilazane layer has a thickness of 200 to 2500 nm.

10. The process as claimed in claim 1 , wherein the polysilazane layer has a thickness of 200 to 2500 nm on the substrate.

11. The process as claimed in claim 1 , wherein the polysilazane layer has a thickness of 300 to 2000 nm on the substrate.

12. The process as claimed in claim 1 , wherein the hardening step of the polysilazane layer takes place at a temperature in the range of 80 to 200° C.

13. The process as claimed in claim 1 , wherein the heating, irradiation or both is effected over a period of 1 min to 60 min.

14. The process as claimed in claim 1 , wherein the heating, irradiation or both is effected over a period of 1 min to 30 min.

15. The process as claimed in claim 1 , wherein the heating, irradiation or both is conducted in an atmosphere of water vapor-containing air or nitrogen.

16. The process as claimed in claim 1 , wherein the optionally further hardening of the polysilazane layer takes place at a temperature between 60 and 130° C.

17. The process as claimed in claim 1 , wherein the optionally further hardening of the polysilazane layer takes place over a period of 30 min to 1 h.

18. The process as claimed in claim 1 , wherein the sodium is in the form of sodium acetate or sodium tetraborate.

19. The process as claimed in claim 5 , wherein the deposition of a sodium-containing precursor layer is accomplished by vapor deposition of a sodium fluoride.