Quantum dots (QDs) are promising materials for solar energy conversion given their process-ability, absorption profile, and expression of quantization effects that allow for tuning of optical and electronic properties. Although photovoltaics are a promising route for harvesting sunlight, approaches for meeting global energy demands make it necessary to store solar energy in chemical bonds (solar fuels). The focus of this project is the attachment of metal chalchogenide nanoparticles to nanoparticulate tin-doped indium oxide films (nanoITO), a mesopourous, transparent conducting oxide, for use as a photocathode in the reduction of protons to H2. Electrodes coated with nanoITO were synthesized and provide approximately 5 times the surface roughness of planar electrodes as determined by electrochemical and spectrophotometric analysis. We have shown that CdSe QDs can be bound to the surface of a nanoITO electrode through bifunctional organic ligands bound to solution-processed CdSe QDs. UV-vis characterization of the films shows solution-synthesized CdSe QDs attached via organic linkers maintain a narrow distribution of sizes, which is controllable through the initial synthesis. Utilization of these electrodes in photochemical and photoelectrochemical experiments with methyl viologen (MV2+) as an electron acceptor demonstrate the importance of controlling the quantum dot interfaces to affect electron transfer rates. The use of a sacrificial electron donor in solution gives photochemical reduction of MV2+ as evidenced by the appearance of the strongly absorbing cation radical. When an electrochemical bias is used to fill the holes instead of the sacrificial electron donor, however, MV2+ is not reduced, indicating a slow electron transfer process from the electrode to the QD hole. To combat this slow electron transfer, we have coated the nanoITO electrodes with thin films of ZnTe, a p-type semiconductor with appropriate band energies relative to CdSe such that excitation of the CdSe leads to a hole in the valence band of ZnTe and an electron in the conduction band of CdSe. The films have been characterized by UV-vis spectroscopy and SEM imaging. These electrodes are now being used in the photochemical and photoelectrochemical reduction of MV2+ and show promise as a way to increase electron-hole separation distances to slow down recombination.

CdSe sensitized photocathodes on a mesoporous transparent conducting oxide scaffold

249th National Meeting (2015)

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