Composition-tunable (SbxBi1-x)2S3 solid-solution thin films via close-spaced sublimation

Alloying strategies in Bi- and Sb-based chalcogenide absorbers remain largely unexplored for close-spaced sublimation (CSS), despite their potential for tailoring bandgap and electronic properties. Here, we report for the first time the development of (Sb x Bi 1-x ) 2 S 3 solid solutions by CSS, spanning a holistic processing framework, from ingot synthesis and thermodynamic analysis of the vapor-phase composition to thin-film absorber validation and proof-of-concept device demonstration. Composition-matched (Sb x Bi 1-x ) 2 S 3 source materials (x = 0.1–0.9) were synthesized and systematically screened by CSS, enabling the establishment of composition-dependent growth regimes that yield dense, homogeneous absorber layers across the entire solid-solution range. Structural characterization confirms the formation of single-phase orthorhombic solid solutions with continuous lattice evolution. Optical analysis reveals systematic bandgap tunability, from ∼1.3 eV to ∼1.7 eV, in line with theoretical predictions. Low-temperature photoluminescence measurements, reported here for the first time for CSS-grown (Sb x Bi 1-x ) 2 S 3 films, suggest that radiative recombination involves localized and exciton-assisted processes. Finally, a proof-of-concept solar cell employing a (Sb 0.9 Bi 0.1 ) 2 S 3 absorber is demonstrated, validating the functionality of CSS-deposited solid-solution absorbers and highlighting their potential for customized PV applications.