Interlayer‐Crosslinkable Hole Transport Layer Achieved Highly Efficient and Stable Perovskite Solar Cells

Abstract Dopant‐free small‐molecule hole‐transport materials (HTMs) in inverted perovskite solar cells often suffer from interfacial degradation during solution processing, which compromises charge extraction and device stability. Here, a reactive molecular engineering strategy is presented involving two concurrent reactions: i) radical polymerization of Apronal into a vertically distributed poly(Apronal) (P‐Apronal) network within the perovskite layer, and ii) interfacial thiourea formation via nucleophilic addition between primary amines of Apronal and isothiocyanate (‐NCS) groups in a newly designed HTM, CAZ‐NCS. The ‐NCS moieties, spatially confined within the HTL, undergo thiourea formation with Apronal's amine groups at the buried interface during spin‐coating and thermal annealing, while the vinyl groups of Apronal simultaneously polymerize into a vertically extended network. This chemically cohesive interface boosts both operational robustness and charge extraction. Devices incorporating CAZ‐NCS‐P achieve a power conversion efficiency of 23.52% and retain 94% of their initial performance after 600 h of continuous illumination ( T 80 = 1951 h). This self‐adaptive and spatially programmed interfacial crosslinking strategy offers a new paradigm for stabilizing buried interfaces in solution‐processed optoelectronic devices.