Screened Charge Carrier Transport in Methylammonium Lead Iodide Perovskite Thin Films

While organometal halide perovskites are promising for a variety of optoelectronic applications, the morphological and compositional defects introduced by solution processing techniques have hindered efforts at understanding their fundamental properties. To provide a detailed picture of the intrinsic carrier transport properties of methylammonium lead iodide without contributions from defects such as grain boundaries, we utilized pump-probe microscopy to measure diffusion in individual crystalline domains of a thin film. Direct imaging of carrier transport in 25 individual domains yields diffusivities between 0.74 and 1.77 cm² s^-1, demonstrating single-crystal-like, long-range transport characteristics in a thin film architecture. We also examine the effects of excitation density on carrier diffusivity, finding that transport is nearly independent of photoexcited carrier density between 6 × 10¹⁷ cm^-3 and 4 × 10¹⁹ cm^-3. Transport modeling of the observed density independence suggests that strong carrier-phonon scattering coupled with a large static relative permittivity is responsible for the unusual transport characteristics of methylammonium perovskite.