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Quantum dot and polymer sensitization of single crystal titanium dioxide electrodes




Sambur, Justin, author
Parkinson, Bruce A., advisor
Maciel, Gary E., committee member
Elliott, C. Michael, committee member
Van Orden, Alan K., committee member
Marconi, Mario C., committee member

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The morphology of semiconductor nanocrystals or quantum dots (QDs) and conjugated polymers at the interface of TiO2 is expected to play an important role in the electron injection efficiency of mesoporous sensitized solar cells (SSCs). Atomic force microscopy (AFM) and photocurrent spectroscopy were employed to correlate the interfacial morphology of QDs and polymers with the sensitized photocurrent yields on planar TiO2 single crystal electrodes. QDs prepared by the ex situ ligand exchange method, whereby 3-mercaptopropionic acid (MPA)-capped QDs were synthesized and directly adsorbed onto bare TiO2 single crystals, resulted in both reproducible sensitized photocurrents and predominantly single layer surface coverages. Photoluminescence (PL) and photocurrent measurement techniques were simultaneously employed to detect electron injection from QDs to TiO2 for a variety of long and short alkyl chain capping ligands. Quenching of the PL lifetime, often interpreted as a spectroscopic signature for electron transfer, was observed for QDs capped with long chain ligands that do not produce sensitized photocurrent. The ex situ ligand exchange procedure was also utilized to adsorb single layers of MPA-capped CdSe/ZnS core/shell (CS) and PbS QDs onto single crystal TiO2 electrodes. Despite a potential energy barrier for photo-excited carriers in the CdSe core imposed by the wide band gap ZnS shell, type-I CS QDs effectively sensitized single crystal TiO2 electrodes and continued to operate in a regenerative mode in an aerated, corrosive iodide electrolyte for more than 20 h. PbS quantum dots adsorbed on TiO2 single crystals exhibited for the first time hot electron injection from higher QD excited states and absorbed photon-to-current efficiencies greater than 100% due to multiple exciton collection. The nanoscale morphology and photoactivity of conjugated polyelectrolytes (CPEs) deposited from different solvents onto single crystal TiO2 was investigated with atomic force microscopy (AFM) and photocurrent spectroscopy. Absorbed photon-to-current efficiencies approaching 50% were measured for CPE layers as thick as 4 nm on TiO2. The research herein suggests that controlling surface morphology of QD and polymer sensitizers may lead to the development of inexpensive, high-efficiency sensitized solar cells.


2011 Summer.
Includes bibliographical references.

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quantum dots
dye sensitized solar cells


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