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 (T80 = 1951 h). This self-adaptive and spatially programmed interfacial crosslinking strategy offers a new paradigm for stabilizing buried interfaces in solution-processed optoelectronic devices.