Binary-mixed organic electron transport layers for planar heterojunction perovskite solar cells with high efficiency and thermal reliability

The optimal electron transport layer (ETL) is a crucial component in the inverted perovskite solar cells (PSCs) for achieving high photovoltaic performance and device stability. We herein address the alloy ETL strategy, which incorporates a non-fullerene small molecule, ITIC-4F, into the fullerene-based ETL to optimize the electron-selective interfacial properties of CH₃NH₃PbI₃-based inverted PSCs. The alloy ETL exhibited tailored energy level alignment at the interface of perovskite and ETL, so the electron-extraction/recombination behavior is greatly improved. Also, the hydrophobic surface of the alloy ETL effectively impedes not only moisture invasion but also morphological deterioration under continuous operation, so the resultant CH₃NH₃PbI₃-based inverted device modified with the alloy ETL exhibited superior power conversion efficiency (PCE) up to 19.99%, with a negligible hysteresis. The alloy ETL-based PSCs also achieves 25.1% efficiency under indoor lighting condition, which promises a feasible design strategy of interfacial optimization in high-performance PSCs using organic semiconductors.