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 (MAPbI3) and cesium lead bromide diiodide (CsPbBrI2). By correlating photoinduced changes to the refractive index with a direct measure of carrier diffusion, both the carrier optical mass and mean scattering time are uniquely determined on microscopic length scales. These results show that the factor of 4 lower mobility of CsPbBrI2 is due not to differing optical masses of charge carriers, which are measured to be similar in CsPbBrI2 and MAPbI3, but rather to a difference in mean carrier scattering time. The scope and limitations of the approach are discussed.