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

Abstract 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 (SnO 2 ) ETL is introduced as a novel interfacial layer for high‐efficiency PSCs. The modified SnO 2 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 SnO 2 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 N 2 . 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.