Reduction of secondary phases in Cu2SnSe3 absorbers for solar cell application

The creation of secondary phases, such as Cu2−xSe and SnSe, and their influence on electrical properties of Cu2SnSe3 (CTSe) thin films fabricated by selenization of Cu-Sn metal precursors are investigated. The Cu2−xSe content in CTSe films is estimated via deconvolution of grazing incidence X-ray diffraction (GIXRD) patterns, and the results suggest that the Cu2−xSe content increases with the increasing Cu/Sn ratio in metal precursors. We also found that using Se and SnSe mixture powders as Se source is an effective approach to suppress the creation of Cu2−xSe secondary phase. Meanwhile, selective etching of Cu2−xSe is realized by potassium cyanide (KCN) solution. Hall measurement results reveal that the secondary phase of Cu2−xSe rather than SnSe makes major contribution to the high carrier concentration (larger than 1018 cm−3) of CTSe films. The approach to further decrease the carrier concentration in CTSe films is discussed.