Multidentate Chelation Modulates PbI ₂ Crystallization and Buried‐Interface Formation in Perovskite Solar Cells

ABSTRACT The buried interface in two‐step processed perovskite solar cells (PSCs) remains a major performance‐limiting factor, primarily due to incomplete PbI 2 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 Pb 2+ directs the formation of porous PbI 2 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 0.84 MA 0.16 PbI 3 ‐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 0.98 Cs 0.02 PbI 3 ‐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 PbI 2 template engineering and buried‐interface optimization in high‐performance PSCs.