Lead–Free Perovskite Solar Cells: A Review

Metal halide-based perovskites (ABX3) have garnered significant attention since 2012 due to their potential to revolutionize the photovoltaic industry, surpassing the performance of traditional silicon solar cells. However, the presence of lead in these materials has raised serious environmental toxicity concerns, hindering their commercial scalability. This limitation has prompted extensive research into lead-free perovskite solar cells (PSCs), which offer a sustainable alternative despite their relatively lower power conversion efficiencies (PCE). Lead-free PSCs leverage materials such as tin (Sn), germanium (Ge), and bismuth (Bi) to achieve non-toxic and environmentally friendly solar cells. Among these, Sn-based perovskites like MASnI₃, FASnI₃, and CsSnI₃ have shown promise due to their direct bandgaps and eco-friendly degradation products, though their PCE is limited by factors such as heavy p-type doping. Germanium-based perovskites, though less efficient due to wider bandgaps, have shown potential when alloyed with other elements. Double halide perovskites (A₂M⁺M³⁺X₆), particularly Bi-based materials, offer improved stability but struggle with low carrier mobility and transport. Device architecture plays a critical role in enhancing the performance of lead-free PSCs, with inverted planar structures (p-i-n) demonstrating superior stability and charge transport efficiency compared to traditional mesoporous configurations. This review highlights the key advances, limitations, and future directions in lead-free PSC research, emphasizing the need for continued innovation in material development, device engineering, and encapsulation techniques to pave the way for environmentally sustainable and efficient solar energy solutions.