By Prashant V. Kamat
During the last century the worldwide population quadrupled and the energy demand increased by sixteen times. The exponential growth in the energy demand is exhausting our fossil fuel supply at an alarming rate. [1, 2]
About 14 terawatts (TW) of energy is currently needed to sustain the lifestyles of 6.5 billion people worldwide. By the year 2050, we will need an additional 10 TW of environmentally clean alternative energy to sustain current lifestyles across the globe.
Three major options are at our disposal to supply the additional 10 TW of clean energy in the coming years: carbon-neutral energy (fossil fuel in conjunction with carbon sequestration), nuclear power, and renewable energy.
Although renewable energy, such as solar power, is ideal to meet the projected demand, it requires new initiatives to harvest solar photons with greater efficiency.[3, 4] The single crystal silicon-based photovoltaic devices that are commercially available deliver power with a 15% efficiency. These first generation devices suffer from high costs of manufacturing and installation.
The second generation devices consisting of CuInGaSe2 (CIGS), or polycrystalline semiconductor thin films, can bring down the price significantly, but their efficiency must be enhanced to make them practically viable. Now being studied are the third generation devices that can deliver high efficiency while being economically feasible.
The emergence of nanomaterials as the new building blocks to construct light energy harvesting assemblies has opened up new ways to develop next generation light energy conversion devices.5
Department of Energy-funded research at Notre Dame has focused on three major pathways for designing light harvesting assemblies and implementing them in energy conversion devices. These include (1) mimicking photosynthesis with donor-acceptor molecular assemblies or clusters; (2i) semiconductor-assisted photocatalysis to produce fuels such as hydrogen; and (3) semiconductor nanocrystal-based solar cells.
Efforts are being made to design organic and inorganic hybrid structures that exhibit improved selectivity and efficiency toward light-energy conversion. Of particular interest are the size-dependent properties such as quantization effects in semiconductor nanocrystals and quantized charging effects in metal nanoparticles.
The use of nanostructures with well defined geometrical shapes (e.g., solid and hollow spheres, prisms, rods, wires) and the ability to organize them into 2- and 3- dimensional assemblies will expand our capability to implement new strategies for light-energy conversion.
Bibliography
1. Hubbert, M. K., The world’s evolving energy system. Am. J. Phys., 1981, 49, 1007-1029.
2. Weisz, P. B., Basic Choices and Constraints on Long-Term Energy Supplies. Physics Today, 2004.
3. Schiermeier, Q.; Tollefson, J.; Scully, T.; Witze, A.;Morton, O., Energy alternatives: Electricity without carbon_. Nature, 2008, 454,_ 816-823.
4. Armaroli, N.;Balzani, V., The Future of Energy Supply: Challenges and Opportunities Angewandte Chemie-International Edition, 2007, 46, 52-66.
5. Kamat, P. V., Meeting the Clean Energy Demand: Nanostructure Architectures for Solar Energy Conversion. J. Phys. Chem. C, 2007, 111, 2834 – 2860.
Prashant V. Kamat is professor of chemistry and biochemistry, a senior scientist at the Notre Dame Radiation Laboratory, a concurrent professor in the Department of Chemical and Biomolecular Engineering, and member of Notre Dame’s Energy Center. He has directed Department of Energy-funded solar photochemistry research for more than 20 years, with his work yielding many publications and scholarly honors.
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