Progress of Hole‐Transport Layers in Mixed Sn‐Pb Perovskite Solar Cells

Abstract

Hybrid organic–inorganic lead halide perovskite solar cells (PSCs) have rapidly emerged as a promising photovoltaic technology, with record efficiencies surpassing 26%, approaching the theoretical Shockley‐Queisser limit. The advent of all‐perovskite tandem solar cells (APTSCs), integrating Pb‐based wide‐bandgap (WBG) with mixed Sn‐Pb narrow‐bandgap (NBG) perovskites, presents a compelling pathway to surpass this limit. Despite recent innovations in hole transport layers (HTLs) that have significantly improved the efficiency and stability of lead‐based PSCs, an effective HTL tailored for Sn‐Pb NBG PSCs remains an unmet need. This review highlights the essential role of HTLs in enhancing the performance of Sn‐Pb PSCs, focusing on their ability to mitigate non‐radiative recombination and optimize the buried interface, thereby improving film quality. The distinct attributes of Sn‐Pb perovskites, such as their lower energy levels and accelerated crystallization rates, necessitate HTLs with specialized properties. In this study, the latest advancements in HTLs are systematically examined for Sn‐Pb PSCs, encompassing organic, self‐assembled monolayer (SAM), inorganic materials, and HTL‐free designs. The review critically assesses the inherent limitations of each HTL category, and finally proposes strategies to surmount these obstacles to reach higher device performance.