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ENGRI_1110_Lect13_09_posted

ENGRI_1110_Lect13_09_posted - Photovoltaics Si p-n junction...

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+ - hf Photovoltaics: Si p-n junction
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Photovoltaic Design Photovoltaic Design www.energy.ca.gov
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www.fsec.ucf.edu/pvt/pvbasics panel array
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Issues Issues To p e le c tro de Thic kne s s  o f to p laye r in junc tio n O the r c o ating s
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Efficiency Efficiency One of the most important parameters of the photovoltaic cell is the efficiency defined as: EFFICIENCY = η = Max electrical power produced by the cell Total solar power impinging on the cell 10 W/dm 2 Example: 1dm 1dm η = 10% 1 W η = 20% 2 W It is important to increase as much as possbile the efficiency.
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Challenges/Efficiency Challenges/Efficiency In the  50’s  S i s o lar c e lls  had an e ffic ie nc y  o f ~ 5% By the  e arly 60’s  e ffic ie nc y was  15% S pac e c rafts  and s ate llite s   Fundam e ntal lim it o f ~30%
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Sun Spectrum Sun Spectrum 350 nm 1,100 nm
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www.wikipedia.com Gases in Atmosphere Absorb Radiation
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Solar Energy Map Solar Energy Map
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Shockley-Queisser analysis (1961) It is based on four assumptions: 1- single p-n junction 2- one electron-hole pair excited for incoming photon 3- thermal relaxation of the electron-hole pair energy in excess of the bandgap 4- illumination with unconcentrated sunlight Maximum efficiency of 31% is obtained for a band gap of about 1 eV
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Challenges Challenges Silicon cannot absorb all photons Other losses come from  Fast recombination Thermalization 
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