Cu2ZnSnSe4 absorbers processed from solution deposited metal salt precursors under different selenization conditions

Cu2ZnSnSe4 (CZTSe) thin film solar cells are fabricated by a simple, non-vacuum deposition of metal salts dissolved in non-hazardous solvents followed by selenization in Se atmosphere. Despite a residual carbon-rich layer between the back contact and the CZTSe absorber layer, solar cells with up to 4.28% conversion efficiency are obtained for Cu-poor and Zn-rich CZTSe absorbers. A frequently reported problem, the loss of tin, is investigated with respect to the influence of the selenization conditions such as substrate temperature and selenium partial pressure. EDX point measurements directly confirm that the remaining decomposed layer consists of a mixture of binary ZnSe and Cu2-xSe phases if the substrate temperature is too high and not sufficient Se is supplied.