Multifunctional Molecule-Modified SnO₂–Perovskite Interface for Efficient Planar Perovskite Solar Cells

The electron transport layer (ETL) is one of the determinants for the performance improvement of perovskite solar cells (PSCs). Here, a multifunctional molecule named 4-fluoro-phenylalanine (4-F-Phe) to modify the surface of tin oxide (SnO₂) ETL is introduced as a novel interfacial layer for high-efficiency PSCs. The modified SnO₂ ETLs exhibit an elevated Fermi level, increasing the carrier extraction and suppressing the interfacial recombination. In addition, the various functional groups of the 4-F-Phe realize strong interfacial interactions with both the bottom SnO₂ ETLs and the top perovskite, which reduces trap state density significantly to promote the interfacial charge transport. As a result, power conversion efficiency (PCE) for the 4-F-Phe optimized device reaches 21.91%. Most importantly, the 4-F-Phe optimized device without encapsulation maintains 91% of its initial PCE after 2000 h at 25 °C with a humidity of 50 ± 5%, and 90% of the initial PCE after 1000 h at 80 °C in N₂. In addition, the encapsulated devices maintain 94% of their initial efficiency under continuous 1 sun illumination for 1000 h when tracking the maximum power point at 45 °C. This work provides a new strategy of modifying ETL to simultaneously improve the efficiency and stability of PSCs.