Lone-pair Bi dopants surpass Sb in orbital-defect synergistic regulation for enhanced radiative recombination in AgInS2

AgInS₂, a representative I–III–VI₂ chalcogenide, has garnered significant attention due to its tunable electronic structure, nontoxic nature, and air stability. However, its practical application is hindered by severe nonradiative recombination losses induced by deep-level In_Ag antisite defects, which act as carrier trapping centers. While Sb and Bi doping have been shown to suppress defect states in CuInS₂, their impact on AgInS₂ remains unexplored. This study systematically investigates Sb and Bi doping in AgInS₂ from the perspectives of electronic orbitals interactions and defect regulation. Under S-rich, In-poor, and Ag-moderate conditions, the formation energy of In_Ag defects increases, thereby reducing their concentration. Sb_In and Bi_In emerge as dominant dopant-induced defects, yet they exhibit distinct effects on carrier recombination. Sb doping introduces deep-level states at 1.08 eV below the conduction band minimum through strong Sb–S antibonding interactions, exacerbating nonradiative recombination losses while reducing the radiative recombination coefficient by three orders of magnitude to 1.36×10⁻¹⁶ cm³/s versus intrinsic AgInS₂’s 9.63×10⁻¹³ cm³/s. In contrast, Bi_In defects remain neutral across the Fermi level range, with Bi doping demonstrating superior defect tolerance that effectively suppresses deep-level states and promotes radiative recombination. This enhances the radiative recombination coefficient by one order of magnitude to 1.27×10⁻¹² cm³/s. This study offers critical insights into lone-pair electron effects in Ag-based chalcogenides, contributing to the advancement of sustainable and high-efficiency optoelectronic materials.