Eliminating the excess CuxSe phase in Cu-rich Cu(In,Ga)Se2 by In2Se3 treatment

The residual CuxSe phase results in shunt leakage paths in Cu-rich Cu(In,Ga)Se2 (CIGS) which can cause serious degradation in the conversion efficiency. The conductive atom force microscopy(C-AFM) was employed to obtain a direct evidence of shunt leakage paths in the Cu-rich CIGS thin film. The results reveal that CuxSe phase exists not only near the surface but also inside the Cu-rich CIGS thin films. In order to eliminate the residual CuxSe, it is recommended to deposit a thin layer of In2Se3 on Cu-rich CIGS with subsequent annealing treatment (In2Se3 treatment for short). The In2Se3 treatment can effectively remove CuxSe phase as well as the shunt leakage paths in Cu-rich CIGS thin films and improve the efficiency of Cu-rich CIGS based solar cells from 1.2% to 9.5%. •The excess CuxSe phase exists not only near the surface but also inside the Cu-rich CIGS thin films.•Direct evidence of shunt leakage paths in the Cu-rich CIGS thin film is obtained.•The excess CuxSe phase can be effectively removed by In2Se3 treatment.