Hot electron transfer from PbSe quantum dots molecularly bridged to mesoporous tin and titanium oxide films

•Efficient hot electron transfer occurs in 3 nm PbSe quantum dots molecularly linked by 3-mercaptopropionic acid to mesoporous TiO2 anatase sensitized films at room temperature.•Inefficient hot electron transfer is resolved for 3 nm PbSe quantum dots molecularly linked by 3-mercaptopropionic acid to mesoporous SnO2 sensitized films at room temperature.•We illustrate how, from the overall time-resolved conductivity response, the QD-oxide ET dynamics can be extracted by controlled photo-oxidation of the QDs-oxide system.

The selective extraction of hot electrons to suitable energy contacts is a key aspect towards the development of hot carrier solar cells. Here we employ Time Resolved THz Spectroscopy (TRTS) to evaluate the extent to which hot electron transfer (HET) takes place from the 1Pe states of colloidal 3 nm PbSe quantum dots molecularly linked by 3-mercaptopropionic acid to mesoporous SnO2 and TiO2 sensitized films. For PbSe-3MPA-SnO2 samples, we show that the efficiency of hot electron transfer is negligibly small at room temperature, i.e. within the ∼10% detection limit of our measurements. The impact of spurious signals on TRTS data arising from carrier dynamics regarding QDs aggregates - which can be misinterpreted as HET - is discussed in detail. In contrast, in line with previous reports, hot electron transfer is observed to take place from the Pe states of colloidal PbSe QDs in the PbSe-3MPA-TiO2 system, with an efficiency ⩾80%. These results are rationalized in terms of a stronger donor-acceptor coupling between QD and oxide for the TiO2 electrode when compared with a SnO2 electrode, a factor that ultimately defines the kinetic competition between electron transfer rate towards the oxide and intraband cooling within the QDs.