Stable and eco-friendly inorganic lead-free perovskite solar cells: structural, electronic, and defect engineering

Inorganic lead-free halide perovskites are emerging as promising candidates for stable and environmentally responsible photovoltaic technologies. Replacing volatile organic cations and toxic lead with robust inorganic constituents enables improved thermal and chemical resilience while preserving favorable optoelectronic properties. This review provides a comparative assessment of representative inorganic lead-free perovskites, highlighting how their structures, electronic configurations, and defect chemistry govern carrier generation and transport. By integrating insights from crystallographic stability and interfacial electronic structure, we outline the key principles that underpin efficient device operation. We further identify the remaining challenges that must be addressed to enable competitive performance, including defect management, controlled crystallization, scalable film formation, and reliable long-term stability under coupled stress conditions. Building on these considerations, we propose future directions to guide the rational design of durable, high-performance inorganic lead-free perovskite solar cells. Inorganic lead-free halide perovskites are promising candidates for stable, eco-friendly photovoltaics. This review compares key materials and shows how their structures and defect chemistry affect performance, highlighting remaining challenges and proposing design principles for more durable, high-efficiency solar cells.