Phonon–Electron Scattering Limits Free Charge Mobility in Methylammonium Lead Iodide Perovskites

The nature of the photoconductivity in solution-processed films of methylammonium lead iodide perovskite is investigated by determining the variation of the photoconductive response with temperature. Ultrabroadband terahertz (THz) photoconductivity spectra in the 0.3–10 THz range can be reproduced well by a simple Drude-like response at room temperature, where free charge carrier motion is characterized by an average scattering time. The scattering time determined from Drude fits in the 0.3–2THz region increases from ∼4 fs at 300 K (tetragonal phase; mobility of ∼27 cm2 V–1 s–1) to almost ∼25 fs at 77 K (orthorhombic phase, mobility of ∼150 cm2 V–1 s–1). For the tetragonal phase (temperature range 150 < T < 300 K) the scattering time shows a ∼T–3/2 dependence, approaching the theoretical limit for pure acoustic phonon (deformation potential) scattering. Hence, electron–phonon, rather than impurity scattering, sets the upper limit on free charge transport for this perovskite.