Polyethyleneimine-modified SnO2 electron transport layers enabling defect passivation and interface engineering for scalable and flexible perovskite solar cells

Abstract

Defect passivation and interfacial optimization in the tin oxide (SnO2) electron transport layer (ETL) remain critical challenges in advancing high-efficiency and scalable perovskite solar cells (PSCs). In this work, we report a novel interfacial engineering strategy using polyethyleneimine (PEI) as a multifunctional modifier for SnO2 ETLs. The amine groups in PEI chemically interact with surface hydroxyls, effectively suppressing oxygen vacancies and simultaneously increasing surface energy. This dual effect not only improves interfacial wettability and perovskite crystallization, but also significantly reduces interfacial recombination at the ETL/perovskite absorber. Consequently, PSCs fabricated on PEI-modified SnO2 achieved power conversion efficiencies of 22.58 % (rigid, 1 cm2) and 22.56 (flexible, 0.12 cm2), demonstrating both exceptional performance and compatibility with scalable processing. Our findings establish a simple yet powerful interface modification technique that offers mechanistic insight and practical advancement for the development of next-generation, scalable and flexible perovskite-based photovoltaics.