Defect Chemistry and Chalcogen Diffusion in Thin-Film Cu2ZnSnSe4 Materials

Selenium diffusion in polycrystalline thin-film Cu₂ZnSn(S,Se)₄ (CZTSe) on molybdenum-coated soda-lime glass substrates was investigated by in situ monitoring of the molybdenum back-contact resistance during high-temperature selenization treatments. In these measurements, selenium diffusion through the CZTSe layer results in conversion of the molybdenum layer to MoSe₂, increasing the sheet resistance of the film stack. By monitoring the rate of MoSe₂ formation as a function of annealing temperature, an activation energy of 0.5 ± 0.1 eV has been measured for selenium diffusion in CZTSe. The partial pressure dependence of chalcogen diffusion suggests that chalcogen vacancies are not the defect controlling chalcogen diffusion in thin-film CZTSe.