Fig. 4: Ultrafast large polaron formation and relaxation dynamics of MAPbI₃.

a The transient THz photoconductivity of the MAPbI₃ polycrystalline grains measured at 800 nm (red) and 400 nm (blue) laser excitations, as plotted in the log scale. b Time-resolved THz photoconductivity dynamics normalized to 1, for two different samples, using excitation of 400 nm wavelength. The gray profile represents the pump pulse. c The pump fluence dependences of the quasi-steady-state THz photoconductivity. The solid line is a fit to the data linearly. d A large polaron in MAPbI₃ looks like a lump of negative charge that attracts MA⁺ cations and repels halide anions. e A proposed band diagram and photoexcitation dynamics in MAPbI₃