Kinetic Suppression of Photoinduced Halide Migration in Wide Bandgap Perovskites via Surface Passivation

In this work, we study the kinetics of photoinduced halide migration in FA$_{0.8}$Cs$_{0.2}$Pb(I$_{0.8}$Br$_{0.2}$)$_3$ wide (~1.69 eV) bandgap perovskites and show halide migration slows down following surface passivation with (3-aminopropyl) trimethoxysilane (APTMS). We use scanning Kelvin probe microscopy (SKPM) to probe the contact potential difference (CPD) shift under illumination, and the kinetics of surface potential relaxation in the dark. Our results show APTMS-passivated perovskites exhibit a smaller CPD shift under illumination, and a slower surface potential relaxation in the dark. We compare the evolution of the photoluminescence spectra of APTMS-passivated and unpassivated perovskites under illumination. We find that APTMS-passivated perovskites exhibit more than 5 times slower photoluminescence redshift, consistent with the slower surface potential relaxation as observed by SKPM. These observations provide evidence for kinetic suppression of photoinduced halide migration in APTMS-passivated samples, likely due to reduced halide vacancy densities, opening avenues to more efficient and stable devices.