First-principles study on the alkali chalcogenide secondary compounds in Cu(In,Ga)Se2 and Cu2ZnSn(S,Se)4 thin film solar cells

First-principles calculations show that the alkali-chalcogenide secondary phases in CZTS and CIGS thin films have very weak absorption of the solar light, explaining why these secondary phases are not so detrimental to the photovoltaic performance.363