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

• Cu 2 Zn 1-x Cd x Sn(S,Se) 4 (CZCTSSe) films were fabricated by a water-based solution method. • Doping Cd in Cu 2 ZnSn(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. Kesterite Cu 2 Zn 1- x Cd x Sn(S,Se) 4 (CZCTSSe) alloy thin films were fabricated by the water-based solution approach. The influence of Cd doping on the morphology, phase structure, element valence states, optical, electrical, and device performance were comprehensively examined. Cd was clearly alloyed into the Cu 2 ZnSn(S,Se) 4 (CZTSSe) absorber layer to form the CZCTSSe compound. By controlling the relative Cd content, band gap values (E g) of the CZCTSSe thin films were engineered between 1.10 eV and 1.21 eV. In addition, doping with Cd led to the enhancement of grain growth as well as improvement of the conductivity and photoelectric property of the absorber layer. In particular, the CZCTSSe (x = 0.4) absorber layer exhibited a pure phase, larger grain size, compact and uniform topography, suitable band gap, Cu-poor and (Cd+Zn)-rich composition, higher conductivity and better photoelectric response. Power conversion efficiency (PCE) is improved from 4.37% of the CZCTSSe (x = 0.0) device to 5.16% of CZCTSSe (x = 0.4) device, and the increases of short-circuit current (J sc) achieved to 8.94 mA/cm2. The encouraging results suggest that doping of Cd is an effective way to improve CZTSSe film properties and promote device efficiency. [ABSTRACT FROM AUTHOR]