Isomer‐Induced Steric Effects on Coordination Site Modification for Interface Passivation in Perovskite Solar Cells

Perovskite solar cells (PSCs) have emerged as a leading photovoltaic technology, thanks to their remarkable power conversion efficiency (PCE) and cost‐effectiveness. Despite achieving PCEs over 26%, the interface between the perovskite layer and the electron transport layer continues to be a significant barrier to achieving even higher PCEs and ensuring long‐term stability. This study presents a molecular engineering strategy through stereoisomeric modulation of thiourea derivatives, comparing N , N ′‐diphenylthiourea (DPT) with its structural isomer 1,1‐DPT as interfacial passivators. The distinct spatial configurations of these isomers fundamentally govern their defect‐passivation capabilities. The 1,1‐DPT isomer, featuring optimized bidentate coordination geometry, demonstrates superior binding affinity with undercoordinated Pb 2+ defects through dual SPb and NPb interactions. Both device testing and density functional theory analyses confirm that these stronger bonding interactions lead to a reduction in defect densities. Benefitting from the exceptional passivation properties of 1,1‐DPT, the device achieved an impressive efficiency of 25.86% coupled with superior operational stability. This work establishes a new paradigm for precision molecular design in PSC engineering, demonstrating that strategic manipulation of isomer‐specific adsorption configurations can synergistically address both structural and electronic defects at critical interfaces.