Designing Effective Hole Transport Layers in Tin Perovskite Solar Cells

Beyond collecting hole charge carriers, hole transport layers (HTLs) in perovskite solar cells (PSCs) can play a significant role in determining the perovskite's quality and stability. While diverse prospective HTL materials are explored for high-performance lead-based PSCs, tin-based PSCs predominantly rely on poly(3,4-ethylenedioxythiophene) polystyrenesulfonate (PEDOT:PSS) to achieve power conversion efficiency near 15% and around 1 year of N-2 shelf-storage stability. While tin perovskites exhibit distinct characteristics in terms of crystal defect species, interfacial properties, crystallization mechanisms, and shallow energy levels, device architectures and HTL materials are usually adopted from lead PSCs without tailoring them for tin PSCs. In this regard, the effective design of HTLs in tin PSCs remains not well-explored. In this Perspective, we propose a comprehensive set of effective HTL design factors with a dedicated focus on tin PSCs, aiming at upgrading PEDOT:PSS and modifying other prospective HTLs to ultimately break the current performance limit to be competitive with or beyond lead PSCs.