Research area: Renewable energy applications
QUANTUM DOT AND NANOWIRE SOLAR CELLS
Solution-synthesized semiconductor nanostructures exhibit a number of useful properties that make them attractive building blocks for next generation solar photovoltaics. They include: low manufacturing costs, potential scalability, linear to branched morphologies, as well as multiple exciton generation capabilities. Size-tunable electron affinities, band gaps and corresponding ionization potentials can also be exploited to enhance device performance. The solution processability of these systems simultaneously enables the facile creation of heterojunctions, which can efficiently separate photogenerated charges.
We have previously explored the use of colloidal quantum dots as well as solution-based nanowires to construct nanostructure-sensitized solar cells. These studies have enabled us to develop fundamental insight into charge transfer processes responsible for device performance. Our future studies therefore seek to exploit this knowledge in developing all inorganic devices that take advantage of the improved charge separation efficiencies of hybrid nanostructures. Furthermore, we have recently discovered a procedure for creating macroscopic nanowire yarns that exhibit sizable photoconductivities. These yarns consist of millions of nanowires aligned along the same direction and have lengths as long as 25 cm. Nanowire yarns can be made of a variety of materials (e.g. ZnSe, CdS, CdSe, CdTe, PbS, and PbSe) with mixed compositions possible. We propose that such yarns may eventually be used in developing solar textiles wherein nanowire fabric can be used to construct a solar cell.
HYBRID PHOTOCATALYTIC NANOSTRUCTURES
Rapid developments in the synthesis of low dimensional materials such as colloidal quantum dots and semiconductor nanowires simultaneously mean timely opportunities for advancing the basic science behind solar energy conversion to chemical fuels. As with solar cells, interest in these materials arises because of their unique size- as well as shape-dependent optical, electrical and chemical properties. These size tunable features open up opportunities for enhancing and even controlling fundamental charge separation at the molecular level.
We have therefore pursued the development of hybrid nanostructures based on nanowires. This has entailed developing core/shell nanowire systems to improve charge carrier lifetimes by taking advantage of favorable electronic band offsets present at core/shell heterojunctions. Such systems have since been employed in the photocatalytic generation of hydrogen. At the same time, we have investigated the use of mixed semiconductor/metal nanostructures by decorating both core and core/shell nanowires with noble metal nanoparticles. This has led to sizable increases in nanowire photocatalyst hydrogen generation efficiencies due to the efficient spatial separation of photogenerated charges.