Effect of Na and Ti–doping on photovoltaic properties of CuInS2 solar cells

CuInS2 (CIS) films were deposited on In2S3/TiO2/FTO/glass under air by spray pyrolysis, resulting in superstrate–structured solar cells. We found a significant difference of images between scanning electron microscope and optical microscope, which suggests crystallisation of spray–pyrolysis CIS particles in In2S3 layer. The In2S3 covering layer was confirmed by Auger Electron spectroscopy. Titanium–doping in In2S3 improved fill factor of CIS cells, however, the conversion efficiency was not changed. The best cells were achieved at 4% sodium doping using 350°C hot–plate and their cell parameters are open–circuit voltage = 0.551 V, photocurrent density = 11.65 mA/cm², fill factor = 0.45, and a conversion efficiency = 2.88%.