Over 10% Efficiency Pure Sulfide Kesterite Solar Cells on Transparent Electrode with Cd–Ag Co‐Alloying

The environmentally friendly elements composed of high bandgap pure sulfide Cu2ZnSnS4 (CZTS) semiconductor has broad prospects for building integrated photovoltaic, double‐sided, and semi‐transparent solar cells when fabricated on transparent substrates. The key issues limiting the performance of CZTS solar cells are poor absorber quality and unfavorable band energy alignment causing serious charge carrier recombination. Here, thefabrication of CZTS solar cells are reported on fluorine‐doped tin oxide (FTO) substrates from dimethyl sulfoxide solution and the effects of the Cd and Ag alloying on device performance. Characterizations show that Cd alloying greatly decreases defect concentration and converts Cliff‐type band alignment to favorable Spike‐type, leading to greatly improved current density. Further, Ag alloying eliminates near‐horizontal grain boundaries and passivates defects in both bulk and heterojunction interface, resulting in a champion device with a power conversion efficiency of 10.3%, the highest efficiency pure sulfide CZTS solar cell on FTO substrate. The results demonstrate the great application potential of pure sulfide kesterite solar cells. The pure sulfide Cu2ZnSnS4 (CZTS) solar cells based on FTO transparent substrates are fabricated by the solution method. Cd alloying improves the energy band alignment of the heterojunction and the crystallinity of the absorber, and further Ag alloying passivates the heterojunction interfacial defects and eliminates the near‐horizontal grain boundaries. The Ag–Cd co‐alloying strategy achieves an efficiency of 10.3%.