Screening Links Transport and Recombination Mechanisms in Lead Halide Perovskites

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.