Perovskite Carrier Transport: Disentangling the Impacts of Effective Mass and Scattering Time Through Microscopic Optical Detection.

While carrier mobility is a practical and commonly cited measure of transport, it conflates the effects of two more fundamental material properties: the effective mass and mean scattering time of charge carriers. This Letter describes the correlation of two ultrafast imaging techniques to disentangle the effect of each on carrier transport in lead halide perovskites. Two materials are compared: methylammonium lead tri-iodide (MAPbI) and cesium lead bromide diiodide (CsPbBrI).

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.

Imaging theory of structured pump-probe microscopy.

With sub-micron spatial resolution and femtosecond temporal resolution, pump probe microscopy provides a powerful spectroscopic probe of complex electronic environments in bulk and nanoscale materials. However, the electronic structure of many materials systems are governed by compositional and morphological heterogeneities on length scales that lie below the diffraction limit. We have recently demonstrated Structured Pump Probe Microscopy (SPPM), which employs a patterned pump excitation field to provide spectroscopic interrogation of sub-diffraction limited sample volumes.