For the intrinsic carriers of MAPbBr$_{3}$, the temperature $T$ dependent mobility $mu(T)$ of behaves like $mupropto T^{-1/2}$ in piezoelectric tetragonal phase, $mupropto T^{-1.4}$ in non-piezoelectric cubic phase. But for the photo-generated carriers in other halide perovskites ABX$_{3}$, $mupropto T^{-3/2}$ behavior is typical. Due to the strong interaction of carrier with longitudinal optical phonon, in ABX$_{3}$ the carriers mainly exist as optical polarons. The softness of ABX$_{3}$ renders it without inversion center in tetragonal phase, which allows piezoelectric effect at low carrier concentration. The variations of $mu(T)$ behavior results from (1) the wave vector dependence of the piezoelectric interaction of polarons with acoustic phonons is different from that of ordinary polaron-acoustic phonon interaction; (2) the residual interaction of polaron with 2 longitudinal optical phonons can be ignored at low temperature, but is important at higher temperature; and (3) the concentration of intrinsic carriers is determined by temperature, while the concentration of photo-generated carriers is determined by the incident flux of photons.
Download