Silicon Solar Cell Technologies
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Transcript of Silicon Solar Cell Technologies
Solar cell technologies • First Generation Solar cells
» Silicon wafer based solar cell technologies (300 to 350 μm)
• Second Generation Solar cells» Thin film based solar cell technologiesCdTe, CuInS2 and amorphous‐Silicon (5 to 10 μm)
• Third Generation Solar cells»Organic and nanostructured based solar cell technologies
Production of Silicon• Most widely used semiconductor material for solar cell
applications.
• 90% of world’s solar photovoltaic modules are produced in Si wafers.
• 1975 , world wide PV module production was about 2 MWp
2007, it has grown to 3000 MWp
• Earlier, it was using electronic grad siliconNow, PV industry is looking for solar grade silicon
Various routes for making solar cells from silicon material
Production of Metallurgical grade Silicon (MGS)Arc furnace
98% pure Silicon
Energy consumed in the process is quite high It is in the range of 13 to 15 kWh/KgOut of this 5% only will be used for making electronic grade silicon
Typical impurity concentrations in metallurgical‐grade silicon
Element Concentration (particles per million)
aluminum 1000‐4350 manganese 50‐120
boron 40‐60 molybdenum < 20
calcium 245‐500 nickel 10‐105
chromium 50‐200 phosphorus 20‐50
copper 15‐45 titanium 140‐300
iron 1550‐6500 vanadium 50‐250
magnesium 10‐50 zirconium 20
Production of Electronic grade Silicon (EGS)
SiHCl3(g) + H2 (g) ----- Si (s) + HCl
(a) Production of high purity Silicon containing gases
Si(s) + 3HCl (g) --- SiHCl3 (g) + H2 +Heatat 300 C
SiHCl3 --- SiH4 + SiCl4 + H2
(b) Obtaining electronic grade solid silicon
Seimens reactor
Typical impurity concentrations in electronic‐grade silicon
Element Concentration (particles per billion)
arsenic < 0.001 gold < 0.00001antimony < 0.001 iron 0.1‐1.0boron ≤ 0.1 nickel 0.1‐0.5carbon 100‐1000 oxygen 100‐400
chromium < 0.01 phosphorus≤ 0.3
cobalt 0.001 silver 0.001copper 0.1 zinc < 0.1
Production of silicon wafers
Atomic arrangements of Si atoms in EGS is not goodWhich contains large number of defects.This can be done by Silicon ingots preparationCalled Czochralski (CZ) and Float Zone (FZ) process
Czochralski(CZ) process
Float-Zone (FZ) process
Multicrystalline Silicon IngotsSeveral crystals of different orientations in an ingot
70% silicon solar cells now produced from this material
Cheaper block costing method
Directional solidification
There is a large growth of PV industry (nearly 30%)& relatively small growth in microelectronic industry (< 10%)
During this time Microelectronic industry can not supply theenough Electronic grade silicon for Silicon based solar cells
What is the alternate ? • Solar grade (SoG) Silicon
refining process from MGS
HCl, HF, HNO3, H2SO4
Al, Fe, Cr, Mn, Ni, Ti
Vapour pressure difference
Segregationcoefficient
Impurities are high compared to EGS
Production cost of Silicon as function of impurity level
Process flow for commercial wafer-based solar cells
Alkaline NaOH
Phosphorous
Plasms enhanced chemicalVapour deposition method
SiNx-H
Metall contacts with Al and Ag
Modeled losses from an ideal solar cell
Useful energy29%
Thermalization32%
Sub-bandgaplosses21%
Other losses18%
Incident solar radiation100%
The most noticeable loss mechanism in solar energy conversion relates to the fact that the basic electronic excitation process in Photovoltaics
and also in photochemical processes & photobiological such as photosynthesis
Third GenerationSolar cellsWill address thisproblem
Book Reference
Solar Photovoltaics: Fundamentals, Technologies and Applications
By Chetan Singh Solanki