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

Abstract

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.