Impact of trap filling on carrier diffusion in MAPb Br 3 single crystals

We present experimental evidence showing that the effective carrier diffusion length ${L}_{d}$ and lifetime \ensuremath{\tau} depend on the carrier density in $\mathrm{MAPb}{\mathrm{Br}}_{3}$ single crystals. Independent measurements reveal that both ${L}_{d}$ and \ensuremath{\tau} decrease with an increase in photocarrier density. Scanning photocurrent microscopy is used to extract the characteristic photocurrent ${I}_{\mathrm{ph}}$ 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 $\ensuremath{\sim}13.3$ and $\ensuremath{\sim}13.8\phantom{\rule{0.16em}{0ex}}\ensuremath{\mu}\mathrm{m}$, respectively. A marginal increase in uniform light bias $(\ensuremath{\le}5\ifmmode\times\else\texttimes\fi{}{10}^{15}\phantom{\rule{0.16em}{0ex}}\mathrm{photons}/\mathrm{c}{\mathrm{m}}^{2})$ 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 $\ensuremath{\sim}9.3\ifmmode\times\else\texttimes\fi{}{10}^{6}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$ and $\ensuremath{\sim}1.4\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}9}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{3}\phantom{\rule{0.16em}{0ex}}{\mathrm{s}}^{\ensuremath{-}1}$, 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.