Methylthio Substituent in SAM Constructing Regulatory Bridge with Photovoltaic Perovskites

Inverted (p‐i‐n) perovskite solar cells (PSCs) have experienced remarkable advancements in recent years, which is largely attributed to the development of novel hole‐transport layer (HTL) self‐assembled monolayer (SAM) materials. Methoxy (MeO‐) groups are typically introduced into SAM materials to enhance their wettability and effectively passivate the perovskite buried interface. However, MeO‐based SAM materials exhibit a mismatch in highest occupied molecular orbital (HOMO) levels with perovskite layer due to the strong electron‐donating capability of methoxy group. In this work, we introduced a methylthio (MeS‐) substituent that is superior to methoxy as a highly versatile self‐assembled molecular design strategy. As a soft base, sulfur atom forms a stronger Pb‐S bond than oxygen. Additionally, within the CbzPh series of SAM materials, MeS‐CbzPh demonstrates a more optimal HOMO level and enhanced hole transport properties. Consequently, the MeS‐CbzPh HTL based device achieved an impressive power conversion efficiency (PCE) of 26.01% and demonstrated high stability, retaining 93.3% efficiency after 1000 hours of maximum power point tracking (MPPT). Moreover, in comparison with the commonly used 4PACz‐based SAM molecular series, MeS‐4PACz also exhibited the best performance among its peers. Our work provides valuable insights for the molecular design of SAM materials, offering a highly versatile functional substituent group.