Impact of trap filling on carrier diffusion in MAPbBr3 single crystals

Abstract

We present experimental evidence showing that the effective carrier diffusion length L d and lifetime τ depend on the carrier density in MAPb Br 3 single crystals. Independent measurements reveal that both L d and τ decrease with an increase in photocarrier density. Scanning photocurrent microscopy is used to extract the characteristic photocurrent I ph decay-length parameter L d , which is a measure of effective carrier diffusion. The L d magnitudes for electrons and holes are determined to be ∼ 13.3 and ∼ 13.8 μ m , respectively. A marginal increase in uniform light bias ( ≤ 5 × 10 15 photons / c m 2 ) increases the modulated photocurrent magnitude and reduces the L d parameter by a factor of 2 and 3 for electrons and holes, respectively, indicating that the recombination is not monomolecular. The L d 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 × 10 6 s − 1 and ∼ 1.4 × 10 − 9 c m 3 s − 1 , respectively. Based on the trends of L d 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.