Effects of Ti-incorporation in CuInS2 solar cells

Abstract Titanium has been incorporated in CuInS 2 thin films and devices by diffusion of Ti from the substrate during the CuInS 2 co-evaporation growth process. The CuInS 2 crystal structure is unaffected but the grain size is reduced compared to Ti-free reference samples. X-ray photoelectron spectroscopy shows the presence of TiO 2 at the front of the absorber layer, which appears at the heterojunction interface of the completed CuInS 2 /TiO 2 /CdS/ZnO solar cells. Low temperature photoluminescence spectra show no additional transitions that could be assigned to Ti-based impurity defect levels. Ti-containing cells show conversion efficiencies higher than the Ti-free reference cells due to higher open-circuit voltage (efficiency 11%, V OC =731 mV). No reduction in short circuit current is detected, indicating that the titanium does not introduce additional bulk recombination. Temperature-dependent current-voltage measurements indicate a reduced interface recombination for cells containing Ti, which is attributed to the TiO 2 interlayer detected by X-ray photoelectron spectroscopy.