Constructing Molecular Bridging at the SnO2/Perovskite Interface for Efficient and Stable Perovskite Solar Cells

Interfacial quality at the SnO2 electron transport layer (ETL)/perovskite junction critically governs the electron collection and device performance in n-i-p type perovskite solar cells (PSCs). However, the defects within SnO2 and at the buried interface can impede electron extraction and promote charge recombination. Herein, cesium hexafluorophosphate (CsPF6) was introduced into the SnO2 precursor as an interfacial additive. Calculations and experimental measurements indicate that the F atoms of PF6- coordinate with undercoordinated Sn sites, whereas Cs participates in the formation of an FA-Cs alloyed layer at the buried perovskite surface. These interactions establish a molecular bridge across the SnO2/perovskite junction. The resulting bridge suppresses the interfacial defects, improves the energy-level alignment and physical contact, and regulates the perovskite crystallization. The devices incorporating CsPF6 deliver a champion power conversion efficiency (PCE) of 24.25%. They also show enhanced stability. The unencapsulated devices retain 90.05% of their initial PCE after 1000 h of aging in ambient air. These findings demonstrate that molecular bridging is an effective route to simultaneously improve the efficiency and stability of PSCs.