An overview is given of materials and manufacturing issues throughout the supply chain of the solar silicon photovoltaic industry. The historical evolution of the industry and future projections are discussed. A brief review is then given of each step of the industry supply chain: polysilicon production, crystallisation and wafering, and the design and manufacturing of crystalline silicon solar cells. The chapter concludes with a discussion of emerging and future advance. An overview is given of materials and manufacturing issues throughout the supply chain of the solar silicon photovoltaic industry. The historical evolution of the industry and future projections are discussed. A brief review is then given of each step of the industry supply chain: polysilicon production, crystallisation and wafering, and the design and manufacturing of crystalline silicon solar cells. The chapter concludes with a discussion of emerging and future advances that will enable scaling of the industry to the terawatt level.••silicon photovoltaicssolar cell architecturescrystalline siliconcrystallisationPhotovoltaics (PV) technology is currently the leading provider of solar electric power, substantially ahead of technologies such as solar thermal power stations, Stirling engines and thermoelectrics. PV has enjoyed extraordinarily rapid growth over the last 30 years. Starting as a niche technology providing power for portable electronics and satellites, electrical output from PV has since grown at an average rate of about 35% a year. At present – a snapshot in a continuing growth process – it is widely used for on- and off-grid domestic solar electricity, in remote or mobile applications in farming (e.g. water pumps), rural communities (e.g. lamps, mobile phone chargers, computers), journalism and prospecting (e.g. data transmission, electrical equipment), and, most significantly, it is now increasingly used as a source of utility power in regions with high insolation. Daytime battery charging for electric cars is a significant emerging application.The demands of the international community for rapid growth in renewable energies to mitigate rapid climate change, and of nation states to increase their energy security, has encouraged crucial governmental support for PV technology development in recent years, notably in Europe, the USA, China, India, Japan and several other countries. This has encouraged development of an increasingly mature PV industry, which in the current period of intense com. The first step in producing silicon suitable for solar cells is the conversion of high-purity silica sand to silicon via the reaction SiO2 + 2 C → Si + 2 CO, which takes place in a furnace at temperatures above 1900°C, the carbon being supplied usually in the form of coke and the mixture kept rich in SiO2 to help suppress formation of SiC. Further chemistry is undertaken to fully eliminate SiC from the product. Most of the resultant 'metallurgical grade' (MG) silicon is used for aluminium casting or in the chemical industry. The remainder (currently only a few per cent, but rising rapidly) is further refined in order to manufacture solar cells. An almost negligible proportion (despite the importance of the final product) goes to fabrication of wafers for the electronics industry. In the medium to long term, the rapid and sustained expansion of the PV industry may make it the largest consumer of metallurgical grade silicon. The trends outlined earlier are quantified in Fig. 1.3.After production of MG silicon, the next step in producing material suitable for solar cells is purification, typically by a factor of 106−109. In the past this has been done by the Siemens process, originally developed to produce very high purity silicon for the electronics industry. Although energy, material and potential pollution costs are high, this process has been adapted for production of solar grade silicon, and modifications have been introduced to reduce costs and mi. In this stage of silicon wafer production, polysilicon is melted and recrystallised into single-crystal or multicrystalline silicon, either in the form of large ingots which must be cut into wafers, or directly into wafers. This section describes the two main approaches used in the solar industry – pulling a crystal from a melt and directional soli.
