  For the intrinsic carriers of MAPbBr$_{3}$, the temperature $T$ dependent
mobility $\mu(T)$ of behaves like $\mu\propto T^{-1/2}$ in piezoelectric
tetragonal phase, $\mu\propto T^{-1.4}$ in non-piezoelectric cubic phase. But
for the photo-generated carriers in other halide perovskites ABX$_{3}$,
$\mu\propto T^{-3/2}$ 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.
