Title: Directional charge transfer mediated by mid-gap states: A transient absorption spectroscopy study of CdSe quantum dot/β-Pb_0.33V₂O₅ heterostructures

Abstract

For solar energy conversion, not only must a semiconductor absorb incident solar radiation efficiently but also its photoexcited electron—hole pairs must further be separated and transported across interfaces. Charge transfer across interfaces requires consideration of both thermodynamic driving forces as well as the competing kinetics of multiple possible transfer, cooling, and recombination pathways. In this work, we demonstrate a novel strategy for extracting holes from photoexcited CdSe quantum dots (QDs) based on interfacing with β-Pb_0.33V₂O₅ nanowires that have strategically positioned midgap states derived from the intercalating Pb²⁺ ions. Unlike midgap states derived from defects or dopants, the states utilized here are derived from the intrinsic crystal structure and are thus homogeneously distributed across the material. CdSe/β-Pb_0.33V₂O₅ heterostructures were assembled using two distinct methods: successive ionic layer adsorption and reaction (SILAR) and linker-assisted assembly (LAA). Transient absorption spectroscopy measurements indicate that, for both types of heterostructures, photoexcitation of CdSe QDs was followed by the transfer of electrons to the conduction band of β-Pb_0.33V₂O₅ nanowires and holes to the midgap states of β-Pb_0.33V₂O₅ nanowires. Holes were transferred on time scales less than 1 ps, whereas electrons were transferred more slowly on time scales of ~2 ps. In contrast, for analogous heterostructures consistingmore » of CdSe QDs interfaced with V₂O₅ nanowires (wherein midgap states are absent), only electron transfer was observed. Interestingly, electron transfer was readily achieved for CdSe QDs interfaced with V₂O₅ nanowires by the SILAR method; however, for interfaces incorporating molecular linkers, electron transfer was observed only upon excitation at energies substantially greater than the bandgap absorption threshold of CdSe. Furthermore, transient absorbance decay traces reveal longer excited-state lifetimes (1–3 μs) for CdSe/β-Pb_0.33V₂O₅ heterostructures relative to bare β-Pb_0.33V₂O₅ nanowires (0.2 to 0.6 μs); the difference is attributed to surface passivation of intrinsic surface defects in β-Pb_0.33V₂O₅ upon interfacing with CdSe.« less

Authors:

Milleville, Christopher C. ^[1]; Pelcher, Kate E. ^[2]; Sfeir, Matthew Y. ^[3]; Banerjee, Sarbajit ^[2]; Watson, David F. ^[1]

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+ Show Author Affiliations

1. The State Univ. of New York, Buffalo, NY (United States)
2. Texas A & M Univ., College Station, TX (United States)
3. Brookhaven National Lab. (BNL), Upton, NY (United States)

Publication Date:

Mon Feb 15 00:00:00 EST 2016

Research Org.:

Brookhaven National Lab. (BNL), Upton, NY (United States). Center for Functional Nanomaterials (CFN)

Sponsoring Org.:

USDOE Office of Science (SC), Basic Energy Sciences (BES)

OSTI Identifier:

1328383

Report Number(s):

BNL-112693-2016-JA
Journal ID: ISSN 1932-7447; KC0403020

Grant/Contract Number:  

SC00112704

Resource Type:

Accepted Manuscript

Journal Name:

Journal of Physical Chemistry. C

Additional Journal Information:

Journal Volume: 120; Journal Issue: 9; Journal ID: ISSN 1932-7447

Publisher:

American Chemical Society

Country of Publication:

United States

Language:

English

Subject:

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Center for Functional Nanomaterials