Surface Engineering in Perovskite Solar Cells: Recent Advances in Surface Passivation Group-Containing Hole Transport Layers

Perovskite solar cells (PSCs) are at the forefront of photovoltaic technology, offering exceptional power conversion efficiencies (PCEs) and the promise of low-cost, scalable production. Rapid progress in PSCs has largely been fueled by innovations in device architecture and component optimization. Among these, the interface between the hole transport layer (HTL) and the perovskite layer is crucial, as it not only facilitates efficient hole extraction and transport but also protects the perovskite from environmental degradation. This review highlights recent advancements in engineering this critical interface, focusing on improvements in surface morphology, interface adhesion, energy level alignment, and defect passivation. Special attention is given to the roles of amide, carboxylic acid, phosphonic acid, and halogenide groups in enhancing HTL properties at the perovskite interface. By synthesizing the latest research and experimental insights, this review provides a comprehensive overview of surface passivation's contributions to high-performance PSCs. It also discusses future directions and challenges in optimizing this interface, key to further advancing this promising photovoltaic technology.