Impact of Trap Filling on Carrier Diffusion in MAPbBr3 Single Crystals
Abstract
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 photo-carrier 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 were determined to be ~ 13.3 μm and ~ 13.8 μm respectively. A marginal increase in uniform light bias (≤ 5 × 1015 photons/cm2) increases the modulated photocurrent magnitude and reduces the Ld parameter by a factor of two and three for electrons and holes respectively, indicating that the recombination is not monomolecular. The Ld variations were 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 × 106 s-1 and ~ 1.4 × 10-9 cm3s-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.