Improved open circuit voltage in CuInS2-based solar cells

The conversion efficiency of thin film solar cells based on CuInS ₂ (η=12%) is mainly limited by a moderate open circuit voltage (≈720 mV). This limitation can be overcome by modifying the absorber/buffer interface leading to open circuit voltages exceeding 800 mV. The addition of ZnS to the CuInS₂ as well as adjusting the preparation conditions for the CdS-buffer leads to an increased V _oc. The coevaporation of ZnS or CdS additives and diffusion from precursor layers for two types of fabrication processes has been examined: codeposition of the elements and diffusion of Cu and S into In _xS_y layers. The addition of ZnS leads to Zn-rich segregations on the CuInS₂ surface. No shift of the bandgap due to the Zn incorporation could be measured. Additionally, an improved sulfur incorporation using the binary In₂S₃ as the In and S source was found