Effect of Indium Doping on the Photoelectric Properties of SnS Thin Films and SnS/TiO2 Heterojunctions

This study addresses the need for efficient photoelectric materials by fabricating Indium-doped tin sulfide (SnS-In)/titanium dioxide (TiO2) heterostructure thin films via radio frequency (RF) magnetron sputtering. We systematically investigated the synergistic enhancement of photoelectric properties from both In-doping and the heterostructure design. SnS-In films with controlled In concentrations were prepared by embedding varying numbers of indium pellets into the SnS sputtering target. Our findings reveal that an optimal In doping of 4.93 at% significantly improves the crystalline quality and light absorption of SnS, reducing its band gap from 1.27 eV to 1.13 eV and enhancing carrier concentration and mobility. Subsequently, the optimized SnS-In film combined with TiO2 formed a heterojunction, achieving a peak photocurrent density of 6.36 µA/cm2 under visible light. This is 2.2 and 53.0 times higher than standalone SnS-In and TiO2 films, respectively. This superior performance is attributed to the optimal In3+ doping effectively modulating the SnS band structure and the type-II heterojunction promoting efficient charge separation. This work demonstrates a promising strategy for optoelectronic conversion and photocatalysis by combining In-doping for SnS band structure engineering with TiO2 heterostructure construction.