As a light absorber in photovoltaic applications, hybrid organic-inorganic halide perovskites should
have long and balanced diffusion lengths for both the separated electrons and holes before recombi-
nation, which necessitates high carrier mobility. In polar semiconductors, the room-temperature
carrier mobility is often limited by the scattering between carriers and the lowest-frequency optical
phonon modes. Using terahertz time-domain spectroscopy, we examine the temperature evolution
of these phonon modes in CH
3
NH
3
PbBr
3
and obtained high carrier mobility values using
Feynman’s polaron theory. This method allows us to estimate the upper limit of carrier mobilities
without the need to create photogenerated free carriers, and can be applied to other heteropolar
semiconductor systems with large polarons.