Stable Perovskite Solar Cells with Bulk-Mixed Electron Transport Layer by Multifunctional Defect Passivation

Multifarious electron transport layers (ETLs), especially fullerene derivatives, have been applied in organic–inorganic hybrid perovskite (OIHP) devices owing to their superior optoelectronic properties. However, a PCBM Lewis acid molecule can only passivate the iodine-rich defect sites, which cannot solve the problem of uncoordinated Pb2+ and water oxygen erosion due to the high volatility of halide I– and the hydrophilicity of organic cation MA+. Herein, we introduce a Lewis base, TBA-Azo with an electron-donating Azo moiety, and hydrophobic long alkyl chains into the PCBM layer to form a multifunctional bulk-mixed electron transport layer (MBE). PCBM of MBE can combine with iodine-rich trap sites at the surface and grain boundaries of perovskite. TBA-Azo molecules of MBE can passivate uncoordinated Pb2+ by forming Lewis adducts and isolate water/oxygen at the perovskite surface with hydrophobic alkyl chains. It results in a decrease of trap densities with 1 order of magnitude, effectively inhibiting both bimolecular and trap-induced recombination and thus elongating the carrier lifetime. The passivation of MBE can effectively improve the open-circuit voltage from 1.05 to 1.10 V. Furthermore, three long carbon chain structures of TBA-Azo in MBE can improve the water-resistant ability of OIHP devices, which can maintain 90% of the original PCE after 500 h at the humidity of 50 ± 10%. We believe that the MBE with multifunctional defect passivation provides a strategy for simultaneously achieving high-performance and high-stability OIHP optoelectronic devices.