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Screening Links Transport and Recombination Mechanisms in Lead Halide Perovskites

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journal contribution
posted on 02.06.2019, 00:00 by Casey L. Kennedy, Andrew H. Hill, Erik M. Grumstrup
Excitation-fluence-dependent charge carrier transport and decay dynamics in individual lead bromide perovskite microcrystals were studied using time-resolved pump–probe microscopy. Measurements show that, in contrast to MAPbI3, diffusion in both CsPbBr3 and MAPbBr3 decreases for carrier densities that exceed ∼1018 cm–3. Fits to the carrier–carrier scattering rate in CsPbBr3 and MAPbBr3 indicate that the Coulomb interaction between mobile charges is mediated by an effective dielectric of ε = 11.53 ± 2.23 for CsPbBr3 and ε = 13.01 ± 1.76 for MAPbBr3, values which are a factor of 2–10 lower than reported values of the static dielectric. Excited state decay kinetics, again collected on individual microcrystalline domains, are consistent with a lower effective dielectric for bromide perovskites relative to iodide perovskites. Nonlinear carrier recombination (2nd order and Auger processes) in CsPbBr3 and MAPbBr3 scale more strongly with excitation density than in MAPbI3. Together, these results indicate that low-frequency contributions to the static dielectric, such as low-frequency phonon modes and ionic mobility, have reduced effectiveness screening the rapidly moving mobile charges at room temperature.

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