Lead‐Free Double Perovskites for Perovskite Solar Cells

Perovskite solar cells (PSCs) have achieved a high power conversion efficiency (PCE) with a credible certified value over 25%. More efforts have been devoted to the development of stable and ecofriendly perovskite materials. Lead‐free double perovskites (LFDPs) are a noteworthy choice as a photoactive layer because of their favorable photovoltaic (PV) properties, intrinsic chemical stability, and environmental friendliness. This Review presents various LFDP materials whose structural stability and optoelectronic properties are predicted by theoretical calculations. The synthesis and experimental properties of LFDPs and their applications in PSCs and optoelectronics in pursuing high performance, low toxicity, and functional stability are also reviewed. Perovskites active layers are critical for PSCs, and their appropriate properties are responsible for achieving a high PCE. On the other side, the stability of PSCs under working conditions is a critical requirement for their practical applications. Defect‐ordered perovskites are also presented to provide another outlook on lead‐free perovskite‐based PVs. The introduction and interest toward LFDP in PSCs can represent a viable solution to the toxicity issue, stimulate further research, and bring a real impact to future PV technologies. Stability and toxicity are bottlenecks for halide perovskite solar cells despite their remarkable efficiency. Double halide perovskites with heterovalent metal cations pave a way for lead‐free‐based devices for enhanced stability. This Review summarizes the theoretical and experimental progress of lead‐free double perovskite. The issues, challenges, applications, and future prospects are integrated to provide a full picture.