Enhancement of the photovoltaic performance of Cd-alloyed Cu2ZnSn(S,Se)4 films based on a low-cost water-based solution process

•Cu2Zn1-xCdxSn(S,Se)4 (CZCTSSe) films were fabricated by a water-based solution method.•Doping Cd in Cu2ZnSn(S,Se)4 (CZTSSe) films could promote its grain growth, improve conductivity and photoconductivity.•Doping of Cd is an effective way to improve short-circuit current and efficiency of CZTSSe solar cell device.