Highly transparent ZnS buffer layer prepared by ultrasonic spray pyrolysis for photovoltaic applications

•ZnS thin films are deposited using low-cost ultrasonic spray pyrolysis technique.•Films prepared at 400 °C showed higher transmittance (∼86%) in the visible region.•Sulfur concentration is varied to find the optimum Zn/S ratio.•Films having Zn/S ratio of 0.67 are found to be suitable as window layer.•0.5% efficient AgInS2/ZnS solar cell is fabricated with the optimized sample.

Zinc sulfide thin films are deposited by ultrasonic spray pyrolysis. The substrate temperature and sulfur concentrations are varied to attain suitable property for the application as window layer in solar cells. Films prepared at lower temperature have traces of ZnO phase together with the dominant cubic ZnS phase. At 400 °C with Zn/S ratio of 1/1.5, sample exhibited higher transmittance (∼86%) consistently in the visible region. With an increase in the sulfur concentration transmittance reduced to ∼50%. Band gap varied from 3.5 to 3.8 eV in the films. The existence of single phase ZnS is confirmed through XPS analysis of the optimized sample. 0.5% efficiency is obtained for AgInS2/ZnS solar cells with the optimized ZnS film.