[hk1]-oriented Ag:Sb₂S₃ thin films via Ag doping for high efficiency indoor solar cells

Antimony trisulfide (Sb 2 S 3 ) has emerged as a promising absorber material for indoor photovoltaic applications owing to its ideal bandgap (∼1.73 eV) and high absorption coefficient in the visible spectrum. However, the carrier transport efficiency of Sb 2 S 3 thin films is strongly constrained by their preferential crystallographic orientation, with the [hk1]-oriented films exhibiting approximately 100 times higher resistivity than their [hk0]-oriented counterparts. Herein, we report a facile chemical bath deposition (CBD) strategy to achieve the [hk1]-oriented Ag-doped Sb 2 S 3 thin films by incorporating trace amounts of Ag + ions into the growth solution. The effects of Ag + concentration on the crystal orientation, bandgap, chemical composition, and defect density of the resulting Ag:Sb 2 S 3 thin films, as well as the photovoltaic performance of the corresponding solar cells, were systematically investigated. The results demonstrate that the Ag:Sb 2 S 3 thin film with an optimal Ag doping concentration of 2% exhibits superior [hk1]-orientation, significantly reduced defect density, and enhanced carrier transport properties, while maintaining an ideal bandgap of ∼1.77 eV. As a result, the Ag:Sb₂S₃ solar cell achieves a photoelectric conversion efficiency of 7.01% under AM 1.5 G illumination and up to 17.22% under warm white LED illumination (2762 K, 1000 lx), representing a notable achievement for Sb 2 S 3 -based indoor solar cells.