Solar Photovoltaic Technologies: Solar Photovoltaic Technologies Prof. C.S. Solanki Energy Systems Engineering IIT Bombay Lecture-29


Contents: Contents Brief summary of the previous lecture Production of Si MG-Si, EG-Si Siemens Process, FBR process CZ Si, FZ Si Wafer dicing L29- Lecture-29


Slide3: Solar PV Technologies Wafer based Si solar cells Thin-film solar cells Production of Si Semiconductor Fundamentals, P-N Junction, Solar cell Physics, Solar cell design L29- Lecture-29


Contents- Production of Si: Contents- Production of Si Solar PV Chain Why Si for PV? Demand for Si feedstock Si wafer production process EG poly-Si (Siemens type, FBR) CZ & FZ process of ingot production wafer dicing Si feedstock from various sources Multi-crystalline Si wafers and ribbon Si L29- Lecture-29


Si for PV: Si for PV Solar energy (PV) is a very fast growing market where the basic technology depends on availability of pure Si. This material is today in high demand and a shortage is expected. Most analysts assume that silicon will remain the dominant PV material for at least a decade. One of Shell’s energy scenario indicates that solar energy will be the single largest energy source within 2060.  Solar PV would play important role in it L29- Lecture-29


Why Silicon?: Why Silicon? At the time being it is almost the only material used for solar cell mass production Easily found in nature, Silicon oxide forms 1/3 of the Earth's crust It is non-poisonous, environment friendly, its waste does not represent any problems It is fairly easy formed into mono-crystalline form Its electrical properties with endurance of 125°C Si is produced with 99.9999999% purity in large quantities. L29- Lecture-29


Solar PV market: Solar PV market Crossing the GW-level: Last year alone worldwide solar cell production reached 1,256 MW (in 2004), 67 percent increase over the 750 MW output in 2003. Solar PV industry has recorded a growth of 30% in the last decade L29- Lecture-29


Contribution of Si in PV market: Contribution of Si in PV market Others include CdTe, CIGS, C-Si/a-Si (4.5%) Over 90% of solar cell are made of Si L29-


Companies producing Si: Companies producing Si Si Wafer Manufacturers Hemlock (USA) SEH, SUMCO Wacker Chemie (Germany) Tokuyama Soda (Japan) ASiMi (USA) MEMC Electronic Material Inc., (USA) Dedicated manufacturers for PV (wafers and cells) Kyocera (Japan), BP Solar (USA), Shell Solar (USA), Photowatt (France). RWE Schott (USA/Germany) L29- Lecture-29


Wafers for solar cells: Wafers for solar cells Crystal type Single crystal Si wafers Multi-crystal Si Wafers Shape Circular Pseudo square Square L29- Lecture-29


Si Wafer Production: Si Wafer Production High temp, Carbon L29- Lecture-29


Solar PV Chain: Solar PV Chain There are several steps from raw material to power systems L29- Lecture-29


Contents-Si production: Contents-Si production Solar PV Chain Why Si for PV? Demand for Si feedstock Si wafer production process  MG-Si EG poly-Si (Siemens type, FBR) CZ & FZ process of ingot production wafer dicing Si feedstock from various sources Multi-crystalline Si wafers and ribbon Si L29- Lecture-29


Metallurgical grade (MG) Si: Metallurgical grade (MG) Si MG-Si is material with 98-99% purity, Produced in about 1 Million tons per year Produced in countries which cheap electricity and quartz deposits (USA, Europe, Brazil, Australia, Norway) Average price is 2 to 4 $/kg MG-Si is produced by reduction of SiO2 with C in arc furnace at 1800 oC. SiO2 + C  Si + CO2 Application in producing chlorosilane for electronic grade Si production, production of Al and Steel Typical impurities are iron, aluminium, calcium and magnesium L29- Lecture-29


Silane and Chlorosilane for Prime Poly Si: Silane and Chlorosilane for Prime Poly Si Electronic grade (EG-Si), 1 ppb Impurities ,99.99999999% MG-Si EG-Si: impurities reduction by five order of magnitude is required  convert MG-Si to gaseous chlorosilanes or silane, purified by distillation For instance Trichlorosilane SiHCl3 and silane SiH4 On chlorination of MG-Si Si + 2Cl  SiCl4 The following reactions result in tri-chlorine-silane gas: SiCl4 + HCl  SiHCl3 L29-


Siemens type reactor: Siemens type reactor • Deposition process is slow 10 days/ton using 12 Siemens reactors Generate by-products containing chlorine• Wacker, Hemlock, Mitsubishi, Tokuyama, Sumitomo SiTiX, MEMC Italia L29- Lecture-29


Fluidized bed reactor (BFR): Fluidized bed reactor (BFR) Continuous process  considerably higher production rates and lower energy consumption Yielding silicon of the highest purity Silicon seed particles are held in suspension by a gas mixture (H2 and SiH4) At 600°C gas phase decomposition takes place, causing the seed particles to grow up to 2 mm in size Big particles falls due to weight Si is collected from the bottom of the jar L29- Lecture-29


Czochralski (CZ) process: (CZ Si wafer): Czochralski (CZ) process: (CZ Si wafer) • Poly-EGS is melted in a quartz crucible (SiO2) • Seed particle introduced to begin crystallization • Seed pulled to generate desired wafer diameter • Ingot is cooled • Crucible is discarded (warping and cracking) L29-