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.