Strengthened Perovskite/SAM Heterointerface for Stable Perovskite Solar Cells

The commercialization of perovskite solar cells (PSCs) is hindered by the long-term mechanical instability of the perovskite/self-assembled monolayer (SAM) interface. This challenge primarily arises from poor interfacial wettability and weak bonding between the SAM and the perovskite. According to the Hard–Soft-Acid–Base (HSAB) theory, a thiol group (−SH), as a soft base, has a strong tendency to form robust bonding with metal ions (such as Pb2+ and Ni2+). Consequently, we designed a series of thiol cross-linkers to construct stable and reliable heterointerface. We found that multithiol cross-linkers not only form chemical bonds with substrates but also retain a portion of unbound −SH at the interface, thereby creating a favorable environment for the growth and bonding of the perovskite. Among them, trimethylolpropane tris(3-mercaptopropionate) (TMP) exhibited the most outstanding performance, and the TMP strategy led to a 1.8-fold increase in the fracture load of the heterointerface and effectively mitigated interfacial degradation. As a result, PSCs treated with TMP achieved a power conversion efficiency (PCE) of 26.16%, independently certified at 25.11%. After continuous operation for 1200 h, the TMP-treated PSCs retained 97% of their initial PCE. Additionally, these devices maintain 90% of their PCE after 1600 h at 85 °C. This work underscores the critical connection between device stability and the mechanical integrity of the heterointerface, presenting a promising strategy for developing long-term stable PSCs.