Issue 30, 2016

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

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

Supplementary files

Article information

Article type
Paper
Submitted
02 Jun 2016
Accepted
05 Jul 2016
First published
05 Jul 2016

Phys. Chem. Chem. Phys., 2016,18, 20466-20475

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

To request permission to reproduce material from this article, please go to the Copyright Clearance Center request page.

If you are an author contributing to an RSC publication, you do not need to request permission provided correct acknowledgement is given.

If you are the author of this article, you do not need to request permission to reproduce figures and diagrams provided correct acknowledgement is given. If you want to reproduce the whole article in a third-party publication (excluding your thesis/dissertation for which permission is not required) please go to the Copyright Clearance Center request page.

Read more about how to correctly acknowledge RSC content.

Social activity

Spotlight

Advertisements