Impact of trap filling on carrier diffusion in MAPbBr3 single crystals

We present experimental evidence showing that the effective carrier diffusion length Ld and lifetime τ depend on the carrier density in MAPbBr3 single crystals. Independent measurements reveal that both Ld and τ decrease with an increase in photocarrier density. Scanning photocurrent microscopy is used to extract the characteristic photocurrent Iph decay-length parameter Ld, which is a measure of effective carrier diffusion. The Ld magnitudes for electrons and holes are determined to be ∼13.3 and ∼13.8μm, respectively. A marginal increase in uniform light bias (≤5×1015photons/cm2) increases the modulated photocurrent magnitude and reduces the Ld parameter by a factor of 2 and 3 for electrons and holes, respectively, indicating that the recombination is not monomolecular. The Ld variations are correlated to the features in photoluminescence lifetime studies. Analysis of lifetime variation shows intensity-dependent monomolecular and bimolecular recombination trends with recombination constants determined to be ∼9.3×106s-1 and ∼1.4×10-9cm3s-1, respectively. Based on the trends of Ld and lifetime, it is inferred that the sub-band-gap trap recombination influences carrier transport in the low-intensity excitation regime, while bimolecular recombination and transport dominate at high intensity.