Light Energy Conversion
Light as Energy
Figure. Designing a system with a Type I band alignment (left) promotes radiative recombination (i.e. when the excited electron loses energy it gives off a photon) which can be useful in LEDs. A Type II band alignment (right) can provide long lived excited electrons which can be used for photocatalysis or solar cells.
All light is made of photons, small "packets" of energy, the energy of which depends on the color, or wavelength, of the light. When a material absorbs a photon of light, the energy of the photon is transferred to an electron in the material, we call this an excited electron. This process is happening all of the time in every colored object that we see - the dye molecules in a red shirt are constantly absorbing blue, green, and yellow photons and reflecting red photons back to our eyes. In most objects, soon after the photon's energy is transferred to an electron, the electron loses that energy as heat, but, if the system is designed correctly, we can use that excited electron to do work. Depending on the system, these excited electrons can be driven through a wire as in a solar cell, or they can be used directly to perform a reaction as in solar hydrogen production.
Harvesting Light with Nanostrucures
Figure. Schematic of the different charge transfer pathways in a Quantum Dot Solar Cell.
During the last decade, nanomaterials have emerged as the new building blocks to construct these types of light energy harvesting assemblies. Organic and inorganic hybrid structures that exhibit improved selectivity and efficiency towards catalytic processes have been designed. Size dependent properties such as size quantization effects in semiconductor nanoparticles and quantized charging effects in metal nanoparticles provides the basis for developing new and effective systems. These nanostructures provide innovative strategies for designing next generation energy conversion devices. Recent efforts to synthesize nanostructures with well defined geometrical shapes (e.g., solid and hollow spheres, prisms, rods, wires) and their assembly as 2- and 3- dimensional assemblies has further expanded the possibility of developing new strategies for light energy conversion.
There are three major ways that one can utilize nanostructures for the design of solar energy conversion devices. The first is to mimic the photosynthesis with donor-acceptor molecular assemblies and clusters. The second is the semiconductor assisted photocatalysis to produce fuels such as hydrogen. The third, and most promising category, is the nanostructure semiconductor based solar cells.
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Our Research Focus
Figure. Design of a photocatalytic water splitting system utilizing Pt/TiO2/IrO2 where TiO2 is used as the light absorber, Pt as the hydrogen evolution catalyst, and IrO2 as the oxygen evolution catalyst.
- Design heterogeneous assemblies consisting of carbon nanostructures (graphene, fullerenes, carbon nanotubes, etc.), semiconductor nanostructures, metal nanoparticles and sensitizing dyes for harvesting light energy
- Elucidate the interfacial charge transfer processes in semiconductor/sensitizer systems
- Design nanostructured assemblies for the direct splitting of water into hydrogen and oxygen gas
- Achieved a photoconversion efficiency (IPCE) of 80% and power conversion efficiency of 5.4% in a Mn:CdS/CdSe quantum dot solar cell
- Employed graphene as an electron scaffold for improved charge transport in nanostructured semiconductor films
- Designed inorganic-organic hybrid assemblies for photoelectrochemical conversion of light energy
- Demonstrated the concempt of the reverse fuel cell for the continuous production of hydrogen using light
424. Fortification of CdSe Quantum Dots with Graphene Oxide. Excited State Interactions and Light Energy Conversion. Lightcap, I. V.; Kamat, P. V. J. Am. Chem. Soc., 2012, 134 (16), 7109–7116.
423. Synchronized energy and electron transfer processes in covalently linked CdSe-squaraine dye-TiO2 light harvesting assembly. Choi, H.; Santra, P. K.; Kamat, P. V. ACS Nano 2012, 6 (6), 5718–5726.
422. Boosting the Efficiency of Quantum Dot Sensitized Solar Cells Through Modulation of Interfacial Charge Transfer. Kamat, P. V. Acc. Chem. Res. 2012, ASAP.
420. Mn-Doped Quantum Dot Sensitized Solar Cells. A Strategy to Boost Efficiency over 5% Santra, P. K.; Kamat, P. V. J. Am. Chem. Soc. 2012, 134 (5), 2508–2511.
418. Sun-believable Solar Paint. A Transformative One-Step Approach for Designing Nanocrystalline Solar Cells Genovese, M.; Lightcap, I. V.; Kamat, P. V. ACS Nano 2012, 6 (1), 865–872.
417. Supersensitization of CdS Quantum Dots with NIR Organic Dye: Towards the Design of Panchromatic Hybrid-Sensitized Solar Cells Choi, H.; Nicolaescu, R.; Paek, S.; Ko, J.; Kamat, P. V. ACS Nano 2011, 5, 9238–9245.
415. Role of Water Oxidation Catalyst, IrO2 in Shuttling Photogenerated Holes Across TiO2 Interface Meekins, B. H.; Kamat, P. V., J. Phys. Chem. Lett. 2011, 2, 2304-2310.
411. CdSe Quantum Dot-Fullerene Hybrid Nanocomposite for Solar Energy Conversion: Electron Transfer and Photoelectrochemistry Bang, J. H.; Kamat, P. V. ACS Nano 2011, 5 (12), pp 9421–9427.
404. Graphene-based Nanoassemblies for Energy Conversion Kamat, P. V. J. Phys. Chem. Lett. 2011, 2, 242-251. (Perspective article)
399. Electron Transfer from Quantum Dots to Metal Oxide Nanoparticles: Theory, Experiment, and Implications Tvrdy, K.; Frantszov, P.; Kamat, P. V. Proc. Natl. Acad. Sci. U.S.A. 2011, 108, 29-34.
400. Beyond photovoltaics: semiconductor nanoarchitectures for liquid junction solar cells Kamat, P. V.; Tvrdy, K.; Baker, D. R.; Radich, J. G. Chem. Rev. 2010, 110, 6664–6688.
387. Nanotechnology for Next Generation Solar Cells Kamat, P. V.; Schatz, G. J. Phys. Chem. C 2009, 15473–15475. (Editorial)
385. Fuel Cell Geared in Reverse. Photocatalytic Hydrogen Production using a TiO2/Nafion/Pt Membrane Assembly with No Applied Bias Seger, B.; Kamat, P. V. J. Phys. Chem. C 2009, 113,18946–18952. NDRL 4820