Multidentate Chelation Modulates PbI₂ Crystallization and Buried-Interface Formation in Perovskite Solar Cells

The buried interface in two-step processed perovskite solar cells (PSCs) remains a major performance-limiting factor, primarily due to incomplete PbI₂ conversion and defect-induced nonradiative recombination. Here, we demonstrate a rational molecular engineering strategy by employing a multifunctional additive, pentaerythritol tetrakis(2-mercaptoacetate) (PTAC-SH), featuring synergistic thiol and carbonyl coordination sites. Multidentate chelation between PTAC-SH and Pb²⁺ directs the formation of porous PbI₂ scaffold, enabling efficient infiltration, and conversion of organic salts. Notably, PTAC-SH spontaneously enriches at the buried interface during crystallization, enabling in situ and targeted passivation of interfacial defects. Consequently, PTAC-SH simultaneously regulates crystallization to yield large-grained, high-quality perovskite films, effectively passivates interfacial defects, and optimizes energy-level alignment. As a result, FA_0.84MA_0.16PbI₃-based devices incorporating PTAC-SH achieve a champion power conversion efficiency (PCE) of 25.33% with exceptional operational stability, retaining 95% of the initial PCE after 1700 h of maximum power point tracking. The generality of this approach is further corroborated in FA_0.98Cs_0.02PbI₃-based devices, delivering a champion PCE of 26.07% with a high open-circuit voltage of 1.199 V. This work highlights the pivotal role of structure-guided molecular design for concurrently PbI₂ template engineering and buried-interface optimization in high-performance PSCs.