Fig. 4. Enhancing hot carrier transport by alkali cations.

(A) The TAM images of the carrier transport in RbCsKMAFA at various delay times. Probe energy = 1.65 eV, pump energy = 3.10 eV, and N₀ = 5.0 × 10¹⁷ cm⁻³. The color scale represents the intensity of pump-induced differential transmission (ΔT) of the probe, and every image has been normalized by peak value. Scale bar, 500 nm. (B) Cross sections of the TAM images shown in (A) fitted with Gaussian functions, with the maximum ∆T signal normalized. (C) ${\mathrm{\sigma }}_t^2$ plotted as a function of pump-probe delay time, comparing hot carrier transport in MAFA, RbCsMAFA, and RbCsKMAFA. Probe energy = 1.65 eV. The dashed lines are guide to the eye. More rapid hot carrier transport is observed in RbCsMAFA and RbCsKMAFA than in MAFA. The error bars of ${\mathrm{\sigma }}_t^2$ indicate the uncertainties of the Gaussian fitting. (D) Transport of cooled carriers; ${\mathrm{\sigma }}_t^2$ at time delay >500 ps for MAFA, RbCsMAFA, and RbCsKMAFA at N₀ = 5.0 × 10¹⁷ cm⁻³. (E and F) Longer-range hot carrier transport is observed at higher carrier density for RbCsKMAFA (E) and RbCsMAFA (F). ${\mathrm{\sigma }}_t^2$ plotted as a function of pump-probe delay time under different excitation densities.