Figure 4: Efficient hot-carrier extraction from perovskites NCs.
From: Slow cooling and highly efficient extraction of hot carriers in colloidal perovskite nanocrystals
(a) Flat-band energy level diagram for illustration of the hot-electron extraction from perovskites NCs to Bphen with competing hot-electron cooling pathways. Conduction band minimum (CBM) (or LUMO levels) and valence band minimum (VBM) (or highest occupied molecular orbital (HOMO) levels) of NCs (or Bphen) were determined from UPS and ultraviolet–visible measurements. (b) AFM image of EDT-NC film. (c) Cross-sectional SEM image of EDT-NCs/Bphen bilayer. Scale bar, 100 nm. (d) Normalized TA spectra for about 35 nm-thick EDT-NCs film with/without Bphen following 3.1 eV photoexcitation with <N0> around 0.1. Inset shows the un-normalized TA spectra at 0.8 ps. (e) Hot-carrier temperature as a function of delay time for EDT-NCs film and EDT-NCs/Bphen bilayer at different pump fluences. Dotted arrows show the decrease of the initial hot-carrier temperatures after adding the Bphen layer, indicating effective hot-electron extraction. (f) Pump energy dependence of the hot-electron extraction efficiencies in about 35 nm-thick EDT-NCs/Bphen bilayer. Inset shows the un-normalized TA spectra at 0.8 ps following 2.5 eV photoexcitation with <N0> around 0.1 for about35 nm thick EDT-NCs film with/without Bphen. (g) Perovskite film thickness dependence of the hot-electron extraction efficiencies upon 3.1 eV pump energy excitation for EDT-NCs/Bphen and bulk-film/Bphen. Inset shows the un-normalized TA spectra at 0.8 ps following 3.1 eV photoexcitation with <N0> around 0.1 for about 140 nm-thick EDT-NCs film with/without Bphen. Error bars on the x axis represent the uncertainties in the determination of (f) excess energies and (g) sample thickness and on the y axis represent uncertainties in the determination of extraction efficiencies.
