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Thin Film Solar Cells

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C-Si Technology in Historic Perspective

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PV

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(Amorphus Silicon, a-Si) (Microcrystalline Silicon c-Si) CIS/CIGS( ) III-IV :GaAs( );II-VI CdTe( ) (Dye-Sensitized Solar Cell) (Organic/polymer solar cells)

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(Organic/polymer solar cells) ( 100nm) ( ) NB PDA Konarka ( 4~5%)

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p-i-n n-i-p p n i

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( c-Si) a-Si c-Si ( Sanyo )

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Thin-film solar cells

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Need of raw material

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(Amorphus Silicon, a-Si) BP 2002 World Nuclear Association : Sputtering CVD

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(Amorphus Silicon, a-Si) : ( 5~7%) (MultijuctionCell) 6~8% 18

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a-Si:H Thin-film Solar Cell (UniSolar )

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CIGS CIS CIGS CIGS 19.88 13 (CIS 10%) CIGS 1.02ev 1.68ev >10E4~10E5 -1 1m 99 US$0.03/W

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CIGS

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Chalcopyrite

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CIGS

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CIGS

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CIGS

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CIGS -

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- Co-evaporation

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- Sputtering

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CIGS -

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- electrodeposition

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-Metal Oxide Ink

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CIS 245-kW rooftop, thin-film CIS-based solar electric array, Camarillo, California (Shell Solar Industries. ) 85-kW thin-film CIS-based BIPV facade, North Wales, UK

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CIGS CIGS CIGS CIGS CIGS

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CIGS CIGS ( ) 10 CIGS

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CdTe( ) CdTe (~600 C) 16% 12% CdTe CIS CIGS ( ) 11% CdTe

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CdTe thin film solar cell

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CdTe Film Deposition

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CdTe Katzenbach Juwi Memmingen SAG SAGFirst Solar ----CdTe Rooftop

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(Dye-Sensitized Solar Cell) (TiO2) ( ) ITO : : ( 7~8% 10%) UV ( )

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DSSC

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Advantage of DSSC Ease of fabrication for large area from solution Transparent Conformal and flexible Low cost of manufacturing Dye-Sensitized Solar Cell

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Principle of the DSSC h : photon absorption a : electron injection b : recombination c : e - transport and collection at conducting substrate d : I - oxidation e : I 3 - reduction f : ion transport Basic mechanisms in a DSSC I/I 3 - redox electrolyte dye h TiO 2 TCO Counter electrode a b c d e f 2e - + I 3 3I - 3I - I 3 - + 2e - E

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DSSC

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Principle of Dye-Sensitized Solar cells Dye-Sensitized Solar Cell Low photocurrent could be the result of 1.Inefficient light harvesting by the dye 2.Inefficient charge injection into TiO 2 3.Inefficient collection of injection electron Gratzel, Nature, 2001

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Special Features of a DSSC Semiconductor not excited directly Photo carrier generation & transportation are well separated the probability of recombination can be drastically reduced. Positive charge transport via ion transport in the electrolyte, rather than hole condition No electric field, electron transfer has been described as diffusion J n = n n E cb + q D n n Nanoparticle structure TCO Counter electrode TiO 2 / dye / electrolyte(I - /I 3 - ) glass e- 0

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Performance of Photovoltaic and DSSC Type of cell Efficiency %(cell) Efficiency %(module) Research and technology needs Crystalline silicon 24 10-15 Higher production yields, lowering of cost and energy content Multi-crystalline silicon 189-12 Lower manufacturing cost and complexity Amorphous silicon 13 7 Lower production costs, increase production volume and stability Dye-sensitized nano- structured materials 10-117 Improve efficiency and high- temperature stability, scale up production

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TCO Electrode Role of the TCO electrode in a DSSC Electrons transportation and collection Characteristics High transmittance in visible region ( ) High electrical conductivity ( ) Thermal endurance ( ) Corrosion resistance Energy level not higher than nanoparticle oxide ( ) present the issue still for improving e-e- I T R

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Materials and Processes of TCO Electrodes Materials: ITO, ZnS, ZnO, SnO 2 (energy gap higher than photo energy in visible region) Processes: Sputtering deposition Plasma ion assisted deposition Ref (3)

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Passage of Light Through a Material Incident = Reflection + Transmittance + Absorption related to refractive index, thickness, particle size Depend on E g Particle size effectInterference effect d Substrate n 1 n s n 0 Nano-material transmit lightMicro-material scatter light

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dye Dye Role of dye in a DSSC Photoexciting & injecting electrons into the conduction band of the oxide Characteristics Absorb all light below 900nm (*) Molecular dispersion in nanostructure oxide (*) Carry attachment group(eg. carboxylate or phosphonate) to firmly graft to the oxide surface The Energy level of excited state higher than conduction band of oxide The redox potential sufficient high to be regenerated via electron from the electrolyte Sustain high cycle usage TiO 2 Ru 2+ Ru 2+* Ru 3+ +e - e-e- h

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Common Materials of the Dye General structure: ML 2 X 2 ( L: 2.2-ipyridyl-4,4-dicarboxylic; M: Ru or Os; X: halide,-CN,-SCN ) N3N3 Absorption Spectrum of N 3 and dark gray Dark gray AM1.5 solar spectrum 400 500600700800900 nm A 0 0.5 1.0 1.5 2.0 N3N3 Dark gray

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Oxide Film --one of the major components in a DSSC Role of the oxide in a DSSC Receive electrons from the dye Efficient transport electrons in the media Characteristics Ultra fine structure(nm-crystal, mesoporous) interconnected (*) Good electrical conduction properties (*) Conduction band edge is more negative than HUMO of the dye ultra fine structure enable. TiO 2 nanoparticles 0 0 1000.15 300 800nm 300800nm Single crystal anataseNanocrystal anatase

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Common Materials and Processes of the Oxide film Material: TiO 2 (cheap, non-toxic), ZnO, Fe 2 O 3, Nb 2 O 5, WO 3, Ta 2 O 5, CdS, CdSe Common processes: TiO 2 film TiO 2 particles (Finely divided monodispersed colloidal) Coating, sintering Ti sault Process parameters: Precursor chemistry Hydrothermal growth Temp Binder addition Sintering condition Control: hydrolysis and condensation kinetics Factors influence properties: Material content Chemical composition Structure Surface morphology Grain size, porosity pore size distribution Crystalline form (anatase,rutile..) Hydrolysis -solvent +binder (1-20 m)

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Electron Transport in the DSSC -- An important factor affecting IPCE D e in the porous film