Abstract
This paper reports on UV-mediated enhancement in the sensitization of semiconductor quantum dots (QDs) on zinc oxide (ZnO) nanorods, improving the charge transfer efficiency across the QD-ZnO interface. The improvement was primarily due to the reduction in the interfacial resistance achieved via the incorporation of UV light induced surface defects on zinc oxide nanorods. The photoinduced defects were characterized by XPS, FTIR, and water contact angle measurements, which demonstrated an increase in the surface defects (oxygen vacancies) in the ZnO crystal, leading to an increase in the active sites available for the QD attachment. As a proof of concept, a model cadmium telluride (CdTe) QD solar cell was fabricated using the defect engineered ZnO photoelectrodes, which showed ∼10% increase in photovoltage and ∼66% improvement in the photocurrent compared to the defect-free photoelectrodes. The improvement in the photocurrent was mainly attributed to the enhancement in the charge transfer efficiency across the defect rich QD-ZnO interface, which was indicated by the higher quenching of the CdTe QD photoluminescence upon sensitization.
Highlights
The interfacial chemistry between two semiconductors or a metal and a semiconductor is important in determining the charge transfer across the interface that dictates the performance in areas like catalysis [1], solar cells [2], and other schemes involving charge separation processes
This is especially important in quantum dot (QD) sensitized solar cells (QDSSC), where the quantum dots (QDs) are deposited on oxide supports with the use of linkers, which increases the distance between the two semiconductors and generates lower current densities as compared to linker-free or directly attached QDs [4]
From the corresponding selected area electron diffraction (SAED) pattern and HRTEM images (Figure 2(b)), it can be observed that the QDs are nearly monocrystalline in nature with a diameter of ∼5 nm (Figure 2(b)), which was confirmed by dynamic light scattering based particle size measurement (Supplementary Information Figure S1 in Supplementary Material available online at http://dx.doi.org/10 .1155/2014/919163)
Summary
The interfacial chemistry between two semiconductors or a metal and a semiconductor is important in determining the charge transfer across the interface that dictates the performance in areas like catalysis [1], solar cells [2], and other schemes involving charge separation processes. In a structure comprising a semiconductor QD deposited on top of a high surface area semiconducting nanostructured oxide, like in the sensitized solar cells, the current flowing across the QD-oxide junction is directly proportional to the distance between the QDs and the oxide material [2, 3]. This is especially important in quantum dot (QD) sensitized solar cells (QDSSC), where the QDs are deposited on oxide supports with the use of linkers, which increases the distance between the two semiconductors and generates lower current densities as compared to linker-free or directly attached QDs [4]. Modification of the surface energy of these nonpolar crystal planes by ligand functionalization
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