Origins and influences of metallic lead in perovskite solar cells

Summary

Metallic lead (Pb⁰) impurities in metal-halide perovskites have attracted tremendous research concerns owing to their detrimental effects on perovskite solar cells (PSCs). However, the origins and influences of the Pb⁰ behind this issue have yet to be well understood. Herein, we show that Pb⁰ is hardly formed in the growth of halide perovskites but is easily postformed in the perovskite films with excess PbI₂. It is found that Pb⁰ impurities are decomposition byproducts of residual PbI₂ in perovskites under light or X-ray irradiation. Therefore, PSCs obtained using photodegraded PbI₂ films show large efficiency and stability losses. By contrast, the perovskite devices without detectable Pb⁰ impurities have a much better efficiency and stability. This work reveals the origins and influences of Pb⁰ in halide perovskites and provides a strategy for avoiding the formation of detrimental Pb⁰ byproducts, which would drive further enhancements in device performance of halide perovskite solar cells, detectors, etc.