Silver–bismuth perovskite-inspired materials: chemistry, optoelectronic properties, and emerging applications in photovoltaics and beyond

Silver-bismuth perovskite-inspired materials (Ag-Bi PIMs) encompass halide double perovskites, vacancy-ordered Cs₂AgBi₂I₉, the (Cu)-Ag-Bi-I family, and structurally related chalcogenides and mixed-anion chalcohalides. Despite their structural diversity, these materials share key electronic features with lead halide perovskites, such as octahedral MX₆ motifs and similar band edge physics, and have emerged as promising non-toxic alternatives. This review explores the structural and chemical diversity of this semiconductor family, showing how cation disorder (CD), crystal vacancies, and reduced electronic dimensionality (ED)-leading to flat bands and heavy carriers-contribute to their indirect bandgaps, high exciton binding energies, and moderate charge-carrier mobilities. Recent advances in defect passivation, CD engineering, and ED control have led to promising photovoltaic efficiencies (∼10% for AgBiS₂ under 1 sun illumination and ∼8% for Cs₂AgBi₂I₉ under indoor lighting), alongside unique functional properties, such as pronounced second-harmonic generation, broadband photocatalysis, resistive switching for neuromorphic devices, and high-sensitivity X-ray detection. Emerging insights reveal that homogeneous CD can reduce bandgaps and enhance light absorption, while controlled crystal vacancies induce local structural modifications critical for nonlinear optical responses. By systematically linking the atomic-scale structure to photophysical behaviour and device-level performance, this review traces clear design guidelines-such as enhancing the ED, minimizing deep trap states, and leveraging mixed-anion chemistry-to advance Ag-Bi PIMs from promising lead-free absorbers to versatile platforms for sustainable energy, photonics, and intelligent electronics. We propose a roadmap outlining a three-stage development model focused on material innovation and device optimization for system-level integration, positioning Ag-Bi PIMs as environmentally friendly semiconductors with broad potential in next-generation optoelectronics.