Dual‐Functional Top‐Interface Passivation Using a Thiohydantoin Derivative for High‐Performance Perovskite Solar Cells

ABSTRACT The efficiency and stability of inverted perovskite solar cells (PSCs) are primarily limited by substantial nonradiative recombination losses at the interfaces, particularly the perovskite (PVK)/electron transport layer (ETL) interface. Here, we introduce a versatile passivation strategy that employs a multifunctional molecule, 3‐Phenyl‐2‐Thiohydantoin‐5‐Propionic Acid (PTGA), as an interlayer at PVK/ETL interface. The ─NH─ moieties in PTGA can repair anionic surface defects through hydrogen bonding, whereas its carbonyl (C = O) functionalities in ─COOH effectively passivate the undercoordinated Pb 2+ cations. This cooperative action leads to a marked decrease in interfacial defect concentration. As a result, the approach improves the crystallinity of the active layer, optimizes energy band alignment, boosts electron extraction efficiency, and suppresses nonradiative recombination. The treated inverted solar cells deliver a champion efficiency of 25.13% with improved long‐term storage stability and persistent light illumination stability, substantially outperforming their untreated counterparts. This work provides a profound mechanistic understanding of multisite molecular passivation and delivers a simple yet effective strategy to advance the commercial prospects of perovskite photovoltaics.