The Effects of Incident Photon Energy on the Time-DependentVoltage Response of Lead Halide Perovskites

Tuning the halide composition in semiconductor perovskite materials is relevant for light emitting and absorbing applications, as it significantly affects the dynamics of both the optical and electrical properties. Yet, a precise understanding of how the halide species influence the electrical behavior of the perovskite remains vague and speculative. In this work, we elucidate the transient voltage of two pure-halide perovskite film compositions (CH3NH3PbBr3 and CH3NH3PbI3) to directly compare the role of the halide in ionic species migration. We capture the photovoltage rise and residual voltage relaxation upon switching the illumination ON and subsequently OFF using Kelvin-probe force microscopy. We discover a unique and unforeseen wavelength-dependent voltage decay for CH3NH3PbBr3. Here, high-energy photons induce a more than one order of magnitude slower voltage decline towards equilibrium (i.e. dark conditions) than low-energy photons. Conversely, we find that the CH3NH3PbI3 perovskite composition ha...