Thermo‐Crosslinking Organic Electron Transport Layers for Stable Perovskite Solar Cells Decoded by In Situ Acoustic Resonance

Electron transport layer (ETL) plays a pivotal role in determining the interfacial integrity and operational robustness of n-i-p structured perovskite solar cells (PSCs). Conventional tin oxide based inorganic ETLs are often plagued by inherent point defects, while organic small-molecule ones frequently suffer from limited device efficiency and durability. In this study, we present an innovative molecular design strategy via developing thermo-crosslinking organic ETLs to overcome these persistent interfacial challenges. Novel organic electron transport materials (ETMs) have been successfully designed by strategically incorporating heat-inducible cross-linking triallyl or oxetane functional groups into naphthalene diimide-based conjugation scaffold, respectively. Such cross-linkable ETMs exhibit exceptional electronic properties, facile heat-induced film-forming capability, and enhanced charge transport. Specifically, featuring optimized energy level alignment and superior surface wettability, oxetane-functionalized ETL endowed n-i-p structured PSCs with a champion power conversion efficiency of 25.23%, among the highest values reported for organic ETL-based devices. Non-destructive ultrasonic testing and accelerated aging assessments have been explored for the first time to decode the substantial improvements in interfacial robustness and operational stability under thermal (85°C) and humid conditions (65% relative humidity). This work establishes a versatile material design paradigm for developing robust organic ETLs, paving the way for high-performance and durable perovskite photovoltaics.