How to Reliably Measure Carrier Mobility in Highly Resistive Lead Halide Perovskites with Photo-Hall Experiment
Mobility measurements in highly resistive methylammonium lead iodide (MAPI) are challenging due to high impedance, ion drift, and low mobility. We show that we can address the challenge using intensity-dependent photo-Hall measurements. The key is an improved photo-Hall setup, which enables reliable Hall measurements in the dark and under low-intensity illumination. By tuning the illumination over four orders of magnitude, we get the additional information to simultaneously extract hole mobility, electron mobility, and background doping. For the first time, we show that a MAPI single crystal, exhibiting n-type behaviour in the dark, can show p-type behaviour under light due to the difference in hole and electron mobility. The data partly explains the variability in mobility reported in the literature. We show that one can erroneously extract any mobility from 0 to 25 cm2/Vs if we restrict the experiment to a small range of illumination intensities. For our MAPI (310) crystal, the measured hole and electron mobility is 40 cm2/Vs and 25.5 cm2/Vs, respectively.