Nanotechnology in Solar Energy Conversion
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7-Nanotechnology
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- World energy consumption
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Energy production and use in the United States How much energy do we use? How do we use it? Where do we get it?
Total energy usage (the situation isn’t getting any better) World energy consumption 0 1 2 3 4 5 6 7 8 9 10 1850 1875
1900 1925
1950 1975
2000 year all
oil coal
gas biomass
nuclear Hydro
geothermy sun; wind & other Economics of solar energy cost of production, ¢ per kW-hr (U.S. in 2002) 0 5 10 15 20 25 Coal Gas Oil Wind Nuclear Solar Cost 1950 1960
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5 10 15 20 25 Efficiency (%) Year crystalline Si amorphous Si nano TiO
2 CIS/CIGS
CdTe Efficiency of Photovoltaic Devices Bulk semiconductor photovoltaics Existing photovoltaics are simple, relatively efficient, but are expensive. Charge separation occurs in the bulk (not at an interface) and is driven by the local electric potential gradient. Efficient charge collection requires very pure materials. (Avoid recombination centers.) Dye-sensitized solar cells Light is absorbed by surface adsorbed dye (or nanoparticle) . Charge separation occurs at an interface. Charge migration occurs in a chemical potential (concentration) gradient. N N - O O - O O 3I - 2e - 2e - MLCT Electron injection Ru 2+
3 - TiO 2 cathode
Bulk heterojunction polymer solar cells Light is absorbed primarily by the polymer Charge separation at the polymer/fullerene interface Hole transport through the polymer Electron transport through the fullerene Nanotechnology in solar energy conversion: Nanoparticle based solar cells Application in “dye” sensitized or bulk heterojunction photovoltaics Advantages: Tunable through quantum size effects (quantum confinement) Not sensitive to impurities Possible multiple exciton generation from excitation in the blue regions of the solar spectrum (reverse Auger process). Potentially very efficient. Passive luminescent solar concentrators Total internal reflection directs light to small, highly efficient PV. Two big technical problems: yield 2) self absorption Possible solution: two sizes of core/shell nanorods. Most photon absorption is by smaller (and more numerous) CdSe or CdTe nanorods. Energy transfer from smaller (blue absorbing) to larger (red emitting) nanorods. The spectral difference minimizes self-absorption. Polymer or glass film with aligned nanorods Photo-
voltaic ZnS
Larger bandgap shell passivates the core semiconductor. CdTe/CdS/ZnS lattice matching results in highly luminescent core/shell semiconductor nanorods CdS
CdTe Energy
transfer Total
internal reflection CdTe Download 476.47 Kb. Do'stlaringiz bilan baham: 
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