Complementary Defect Tuned Modulation of Optoelectronic and Catalytic Performance in SnSe via SnCl ₂ and CdCl ₂ Doping

SnCl2 and CdCl2-assisted doping was employed to tune the defect landscape and functional properties of SnSe crystals synthesized by direct vapor transport. Structural and compositional analyses confirm successful dopant incorporation, where SnCl2 passivates Se vacancy-related defects and expands the lattice, while CdCl2 induces controlled lattice distortion via Cd2+ substitution. These effects tune the optical band gap from 1.27 eV in pristine SnSe to 1.49 and 1.38 eV in SnCl2:SnSe and CdCl2:SnSe, respectively. Temperature-dependent transport measurements reveal the elimination of the positive TCR behavior observed in undoped SnSe and the establishment of stable thermally activated conduction in the doped systems. Hall measurements indicate a transition from p- to n-type conduction, accompanied by an increase in the electron concentration, consistent with vacancy passivation and defect compensation. Both doped crystals exhibit modest yet measurable improvements in photocurrent and noise characteristics, while photocatalytic studies show better methylene blue degradation efficiencies, with SnCl2:SnSe outperforming CdCl2:SnSe. These results demonstrate that chloride-based doping tailors SnSe for better optoelectronic and photocatalytic performance effectively.