Recent Advances in Wide Bandgap Perovskite Solar Cells: Focus on Lead‐Free Materials for Tandem Structures

Abstract A tandem solar cell, which is composed of a wide bandgap (WBG) top sub‐cell and a narrow bandgap (NBG) bottom subcell, harnesses maximum photons in the wide spectral range, resulting in higher efficiency than single‐junction solar cells. WBG (>1.6 eV) perovskites are currently being studied a lot based on lead mixed‐halide perovskites, and the power conversion efficiency of lead mixed‐halide WBG perovskite solar cells (PSCs) reaches 21.1%. Despite the excellent device performance of lead WBG PSCs, their commercialization is hampered by their Pb toxicity and low stability. Hence, lead‐free, less toxic WBG perovskite absorbers are needed for constructing lead‐free perovskite tandem solar cells. In this review, various strategies for achieving high‐efficiency WBG lead‐free PSCs are discussed, drawing inspiration from prior research on WBG lead‐based PSCs. The existing issues of WBG perovskites such as V_OC loss are discussed, and toxicity issues associated with lead‐based perovskites are also addressed. Subsequently, the natures of lead‐free WBG perovskites are reviewed, and recently emerged strategies to enhance device performance are proposed. Finally, their applications in lead‐free all perovskite tandem solar cells are introduced. This review presents helpful guidelines for eco‐friendly and high‐efficiency lead‐free all perovskite tandem solar cells.