Characterization of electron transfer from CdSe quantum dots to nanostructured TiO 2 electrode using a near-field heterodyne transient grating technique

Abstract

The ultrafast carrier dynamics of the CdSe QDs adsorbed on a nanostructured TiO 2 electrode and on a glass substrate were studied using a near-field heterodyne detection transient grating (NF-HD-TG) method. Two decay processes were observed in the TG responses. The fast decay time constants τ 1 were the same (2.3 ps) for these two kinds of substrates, corresponding to the photoexcited hole relaxation in the CdSe QDs. However, the slow decay time constants τ 2 were very different for these two kinds of substrates, reflecting the photoexcited electron relaxation (i.e., trapping and/or transfer). Since no electron transfer from the CdSe QDs to the glass substrate could occur, we could estimate the electron transfer rate from the CdSe QDs into the nanostructured TiO 2 electrode to be approximately 5.4 × 10 9 s − 1 using the values of τ 2 detected for these two kinds of substrates.