Lead-free perovskites for indoor photovoltaics

With the rapid development of indoor photovoltaics as an energy-efficient solution to power devices in low light conditions, lead-free perovskite materials have emerged as promising candidates. Particularly, tin halide perovskites (THPs) and bismuth halide perovskites (BHPs) are attractive due to their tunable bandgaps, strong optoelectronic performance, and non-toxicity. This review explores their crystallization behavior, defect formation, and indoor-specific challenges, focusing on BHPs as stable, less-toxic alternatives, and evaluating THPs for their optoelectronic merits. We highlight methods to overcome critical barriers—such as defect mitigation via doping, compositional engineering, and controlled crystallization and outline future directions to boost BHPs efficiency, stability, and environmental compatibility in indoor solar harvesting.