Fig. 3: Photo-induced changes of terahertz photoconductivity in CsFAMA thin films.

a The real part and b the imaginary part of the photo-induced change of the terahertz photoconductivity calculated from the time-domain THz spectra recorded at 5 ps delay time for carrier densities varying from 6.9 × 10¹⁷ to 7.5 × 10¹⁸ cm⁻³. The pump wavelength was 550 nm (photon energy ~2.25 eV). All error bars indicate standard errors based on multiple measurements. Dash-dotted lines are fits using the Drude–Smith model (DS model), red solid lines are fits using the Drude–Debye model (DD model). The fits using the Drude–Anderson model (DA model) and Drude–Lorentz model (DL model) are not shown, because they are similar to the DD model fits. c Schematic photoconductivity from Lorentzian resonance and Anderson localization. Although Anderson localization substantially reduces the dc photoconductivity, carrier hopping can overcome the Anderson localization, resulting in a photoconductivity response similar to the Lorentzian resonance. Inset: Scheme of carrier localization caused by polaron (E_p) formation and due to the presence of an energy barrier (E_h).