Fig. 4. Comparison of hot-carrier effects.

a Pseudocolour representation and b Normalized TA spectra at different delay times of 3D bulk perovskite film. The pump laser pulse is 480 nm (2.6 eV) with excitation fluence around 0.13 mJ cm⁻². c Normalized TA spectra of quasi-2D perovskite film at 200 fs delay under different excitation intensities. The pump laser wavelength is 400 nm (3.1 eV). Herein, the energy of the photon $\hslash \omega$ used to excite 3D and quasi-2D perovskites is 2.6 eV and 3.1 eV, respectively, to ensure an equal excess energy (0.9 eV) of initially injected carriers. d Time-dependent hot carrier temperatures of 3D and quasi-2D perovskites, respectively. The pump fluence is maintained at 0.13 mJ cm⁻². e Initial hot-carrier temperature of quasi-2D perovskite film as a function of pump power (pump photon energy of 2.6 eV) and excess energy (inset, the pump fluence is kept at 0.4 mJ cm⁻²). Error bars in d, e represent the uncertainties in the fitting of carrier temperature. f TA kinetics under different excitation fluence pumped with 540 nm femtosecond laser pulse. Green region highlights the non-thermalization carrier kinetics within the first 300 fs. Red arrow outlines the subsequent hot-carrier cooling process after thermalization. The non-thermalized carriers and hot carriers induced absorbance difference is labeled by ΔA_NTC and ΔA_HC. Inset: power-dependent ΔA (hollow dots) at 150 fs delay fitted with Eq. 2 (red solid line).