A Bifunctional Lewis Base Additive for Microscopic Homogeneity in Perovskite Solar Cells

Certified power conversion efficiencies (PCEs) of perovskite solar cells have increased to reach an impressive 22.1%. However, there exists microscopic in-homogeneity that limits high PCE, primarily as a result of defects at grain interiors and boundaries of perovskite films. Here, we report a strategy for reducing heterogeneity by using a bifunctional non-volatile Lewis base additive urea. The addition of 4 mol % urea results in significant enhancement of the macroscopic photoluminescence lifetime from 200.5 to 752.4 ns and elimination of trap-mediated non-radiative recombination, resulting in an improved PCE. The Lewis base urea is found to interact with solution precursors to retard crystal growth and enhance crystallinity, which subsequently precipitates at grain boundaries to passivate defects after completion of crystal growth. The resulting perovskite films show superior homogeneity in conductivity at both grain interior and boundaries in comparison with the bare perovskite films.