Enhancement of electron transfer from CdSe core/shell quantum dots to TiO2 films by thermal annealing

We demonstrated the enhancement of electron transfer from CdSe/ZnS core/shell quantum dots (QDs) to TiO2 films via thermal annealing by means of steady-state and time-resolved photoluminescence (PL) spectroscopy. The significant decrease in PL intensities and lifetimes of the QDs on TiO2 films was clearly observed after thermal annealing at temperature ranging from 100 °C to 300 °C. The obtained rates of electron transfer from CdSe core/shell QDs with red, yellow, and green emissions to TiO2 films were significantly enhanced from several times to an order of magnitude (from ∼107 s−1 to ∼108 s−1). The improvement in efficiencies of electron transfer in the TiO2/CdSe QD systems was also confirmed. The enhancement could be considered to result from the thermal annealing reduced distance between CdSe QDs and TiO2 films. The experimental results revealed that thermal annealing would play an important role on improving performances of QD based optoelectronic devices.