Enhancing electrical properties of Cu2ZnSn(S,Se)4 thin films via trace Co incorporation

Abstract Substitution of Zn2+ ionic by Co2+ ionic is known to suppress the cation disorder of Cu2ZnSn(S,Se)4 thin films, which is helpful to obtain the excellent Cu2ZnSn(S,Se)4 solar cell devices. In our work, the extra trace Co incorporation was added in the solution without affecting the compositions of other elements (i.e. Cu, Zn, and Sn) to enhance the electrical properties of Cu2ZnSn(S,Se)4 thin films. And Co incorporation does not enter into the lattice nor be found in the selenized films after taking effect, but increases the crystallinity, compactness, carrier concentration, and electrical properties of Cu2ZnSn(S,Se)4 thin films samples. By tuning the doping ratios of Co2+ ionic, the surface roughness of the selenized films can be decreased from 110.2 nm (0 mol %) to 68.90 nm (5 mol %). As 1 mol % of Co2+ ionic is doped, the carrier concentration of films can be also improved to 4.35 × 1017 cm−3 from 2.63 × 1016 cm−3, and average surface current of films applied 1 V AC voltage can be increased from 2.426 nA to 4.454 nA. The enhanced properties of Co-incorporated films brings hope for the excellent performance of Cu2ZnSn(S,Se)4 solar cells.