Fabrication strategies for lead-free bismuth-based perovskite solar cells: a review

The certified power conversion efficiency (PCE) of organic-inorganic lead (Pb) halide perovskite solar cells (PSCs) has reached 27% recently, surpassing those of most of the commercialized photovoltaic technologies and emerging as a promising approach for efficient and cost-effective solar energy harvesting. However, the toxicity of Pb in high-performance PSCs remains a significant barrier to their commercialization. To address this issue, non-toxic alternatives such as bismuth (Bi) have been explored. Despite extensive effects, the performance of Bi-based PSCs remains inferior to their Pb counterparts, partially owing to challenges in fabricating high-quality thin films arising from the complex crystallization kinetics and rapid formation processes. This review provides a comprehensive analysis of the fabrication processes of various Bi-based light absorbers. Initially, the structural and optoelectronic properties of these materials are summarized, followed by a systematic discussion of the fabrication techniques, including solution processing, evaporation, and hybrid methods. The performance of different families of Bi-based materials is also summarized. Finally, the challenges and further perspectives for advancing Bi-based perovskites and related derivatives are outlined, offering insights into the development of Pb-free alternatives.