  The formation of Frohlich polaron in metal halide perovskites, arising from
the charge carrierlongitudinal optical (LO) phonon coupling, has been proposed
to explain their exceptional properties, but the effective identification of
polaron in these materials is still a challenge task. Herein, we theoretically
present the infrared optical absorption of Frohlich polaron based on Huang-Rhys
model. We find that multiphonon overtones are appeared as the energy of
incident photon matches the multiple LO phonons, wherein the average phonon
numbers of a polaron can be directly evaluated by the order of the strongest
overtone. These multiphonon structures sensitively depend on the scale of
electronic distribution in the ground state and the dimensionality of the
perovskite materials, which gives the enlightenment for the effective
modulation of competing processes between the polaron formation and carrier
cooling. Moreover, the order of the strongest overtone shifts to the higher
ones with temperature, providing a potential proof of the carriers mobility
affected by LO phonons scattering. The present model not only suggests a direct
way to verify Frohlich polaron, but also enriches the understanding of the
polaron properties in metal halide perovskites.
