Interface Matters: Boosting Efficient Pb‐Sn Perovskite Solar Cells for All‐Perovskite Tandem Photovoltaics

ABSTRACT To overcome the theoretical efficiency limit of single‐junction perovskite solar cells (PSCs), the development of all‐perovskite tandem solar cells (APTSCs) has attracted significant interest due to their low cost, high efficiency, and compatibility with flexible substrates. Currently, the performance of APTSCs is primarily constrained by the inferior performance of narrow‐bandgap lead‐tin (Pb─Sn) perovskite sub‐cells, stemming from poor interface quality caused by Sn ²⁺ instability and an unbalanced crystallization process. Encouragingly, recent breakthroughs in rational interface engineering have enabled the construction of high‐quality Pb─Sn perovskite films with optimized interfaces, boosting the efficiency of APTSCs beyond 30%. Herein, we provide a comprehensive review of the recent advances in interface engineering for realizing efficient Pb─Sn PSCs and APTSCs. First, we introduce the fundamental challenges and potential solutions associated with the different interfaces in Pb─Sn PSCs, including the grain boundaries, buried interface, and top interface. Subsequently, we carefully examine cutting‐edge strategies and their underlying mechanisms for addressing these interface issues of Pb─Sn PSCs, and the corresponding performance of their APTSCs is also summarized. Finally, we offer a critical perspective on this exciting field. This review is intended to inspire new ideas for further performance improvements in Pb─Sn PSCs and APTSCs.