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Issue 30, 2016
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Photoinduced electron transfer from quantum dots to TiO2: elucidating the involvement of excitonic and surface states

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Abstract

Colloidal semiconductor quantum dots (QDs) exhibit excitonic and surface states, both of which may participate in charge-transfer processes relevant to solar energy conversion. To explore this inherent complexity of the charge-transfer mechanisms of QDs, we used steady-state and time-resolved emission measurements to characterize excited-state electron transfer (ET) from core-only CdSe QDs and core/shell CdSe/ZnS QDs to TiO2 nanoparticles (NPs). Core-only QDs transferred electrons from both excitonic and surface states to TiO2 with rate constants of ET (ket) of approximately (1–3) × 108 s−1 and (4–7) × 107 s−1, respectively. Efficiencies of ET (ηet) from excitonic and surface states were approximately 71–82% and 64–76%, respectively. Thus, trapping of electrons lowered their potential energy but did not greatly affect the efficiency of their transfer to TiO2. Photogenerated holes were transferred from core-only CdSe QDs to adsorbed 3-mercaptopropionic acid (MPA), which linked the QDs to TiO2. We characterized core/shell CdSe/ZnS QDs as alternatives to core-only QDs. The ZnS shell eliminated the undesirable trapping of electrons and transfer of photogenerated holes to MPA. We measured ket of approximately (1–3) × 108 s−1 and ηet of approximately 66–85% for ET from excitonic states of core/shell CdSe/ZnS QDs to TiO2 NPs. The insensitivity of ket to the presence of the ZnS shell may have arisen from increased cross-linking of core/shell QDs to TiO2. Our results highlight the involvement of surface states in excited-state ET processes of core-only QDs and, for the heterostructures reported here, the improved performance of core/shell CdSe/ZnS QDs relative to core-only CdSe QDs.

Graphical abstract: Photoinduced electron transfer from quantum dots to TiO2: elucidating the involvement of excitonic and surface states

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Publication details

The article was received on 02 Jun 2016, accepted on 05 Jul 2016 and first published on 05 Jul 2016


Article type: Paper
DOI: 10.1039/C6CP03813A
Citation: Phys. Chem. Chem. Phys., 2016,18, 20466-20475
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    Photoinduced electron transfer from quantum dots to TiO2: elucidating the involvement of excitonic and surface states

    S. Chauhan and D. F. Watson, Phys. Chem. Chem. Phys., 2016, 18, 20466
    DOI: 10.1039/C6CP03813A

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