Cationic Surfactant-Driven Interfacial Engineering Enables 22% Efficient and Stable Perovskite Solar Cells

Interfacial engineering of the electron transport layer (ETL) in perovskite solar cells (PSCs) is a pivotal strategy to suppress charge recombination and enhance both device efficiency and operational stability. In this work, we introduce a novel class of quaternary ammonium-based organic salts, benzalkonium chloride (BAC) and benzalkonium bromide (BAB), as multifunctional cationic surfactants to modify the SnO2 ETL/perovskite interface. These BAC/BAB additives simultaneously passivate interfacial defects while significantly improving the morphological quality of the ETL and perovskite (Cs0.05(FA0.90MA0.10)0.95Pb(I0.90Br0.10)3) layers. The result is an optimized energy level alignment and more efficient charge extraction across the interface. Notably, PSCs incorporating 1.0-BAB (1 mg/mL of BAB) exhibit a remarkable increase in power conversion efficiency (PCE), from 19.8% (control) to 22.0%, alongside improved film uniformity and interface quality. Long-term operational stability, assessed under the prolonged exposure to light (ISOS-L1 protocol), revealed that unencapsulated devices retained 93.6% of their initial PCE after 900 h of continuous operation, whereas control devices degraded to 49.7% within 400 h. This study presents a facile and scalable interfacial modification strategy that addresses one of the most pressing challenges in PSC technology, interfacial instability, offering a promising route toward high-efficiency, durable perovskite photovoltaics.