Abstract
Hot electrons can dramatically improve the efficiency of solar cells and sensitize energetically-demanding photochemical reactions. Efficient hot electron devices have been hindered by sub-picosecond intraband cooling of hot electrons in typical semiconductors via electron-phonon scattering. Semiconductor quantum dots were predicted to exhibit a “phonon bottleneck” for hot electron relaxation as their quantum-confined electrons would couple very inefficiently to phonons. However, typical cadmium selenide dots still exhibit sub-picosecond hot electron cooling, bypassing the phonon bottleneck possibly via an Auger-like process whereby the excessive energy of the hot electron is transferred to the hole. Here we demonstrate this cooling mechanism can be suppressed in copper-doped cadmium selenide colloidal quantum dots due to femtosecond hole capturing by copper-dopants. As a result, we observe a lifetime of ~8.6 picosecond for 1Pe hot electrons which is more than 30-fold longer than that in same-sized, undoped dots (~0.25 picosecond).
Highlights
Hot electrons can dramatically improve the efficiency of solar cells and sensitize energetically-demanding photochemical reactions
A representative transmission electron microscope (TEM) image shows an average diameter of 3.3 ± 0.4 nm for these Cu:CdSe quantum dots (QDs) (Supplementary Fig. 1)
The X band is broadened in doped QDs as compared to undoped ones, the reason for which remains to be elucidated as the size distributions of the doped and undoped QDs are similar (Supplementary Fig. 1)
Summary
Hot electrons can dramatically improve the efficiency of solar cells and sensitize energetically-demanding photochemical reactions. Hot electron lifetime on the order of tens of ps was demonstrated in CdSe/ZnS/ZnSe/CdSe core/multi-shell QDs featuring electron-hole separation, which could be further prolonged by using capping ligands of low infrared absorbance[25,26] The issue with these complicated core/shell structures is that carrier extraction from them can be very difficult which renders them unsuited for solar energy conversion applications. Efficient suppression of hot electron cooling via the phonon bottleneck can be realized in a much simpler system, copper-doped QDs (Cu:QDs) These QDs have been developed for decades and have been extensively studied for their peculiar light emission and photo-induced magnetism properties[27,28,29,30,31,32,33]. Longerlived hot electrons in Cu:CdSe QDs as compared to CdSe QDs a b
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