Electricity is the foundation of the existence and development of human society. The current mainstream of thermal power generation, with the shortage of resources and environmental pollution is increasing, looking for a clean, green, renewable alternative energy to ease the tight supply of coal and thermal power to bring the global environmental pressure, has become the international community Common pursuit of the goal. According to the World Energy Commission forecast data show that the global availability of fossil fuels at least available for human use for about 100 years, but the relatively low cost of mining reserves decreased year by year. This means that the thermal power grid will increase year by year. Among the many alternative energy sources, solar energy reserves, green, widely distributed, much favored by the world. In recent years, the state and local governments to actively promote the solar photovoltaic industry launched a comprehensive, multi-level attempt and efforts, and achieved remarkable results.
1, solar photovoltaic cell classification
Solar cells according to their different materials can be divided into crystalline silicon solar cells, thin film batteries, dye-sensitized batteries and organic solar cells and other categories. Which dye-sensitized solar cells and organic solar cells are still in the experimental development stage, the market share is very low. Figure 1 shows the European Photovoltaic Industry Association (EPIA) listed solar photovoltaic cell classification and market share. Can be seen from Figure 1, crystalline silicon battery is still the mainstream of the photovoltaic industry, the market share of about 9O%. In the field of thin-film batteries, the compound thin-film battery market share of more than 1/2, higher than the amorphous silicon thin-film battery.
1.1 crystalline silicon solar cells
Crystalline silicon solar cells, including monocrystalline silicon and polycrystalline silicon solar cells two, the production process is mature, technical route stability, photoelectric conversion efficiency, high market share. Laboratory research and development of passive emitter back side of the local diffusion (PREI) monocrystalline silicon solar cell light conversion efficiency has reached 24.7%, commercial battery components efficiency of about 17%. However, the special nature of the traditional monocrystalline silicon solar photovoltaic products limits its wide range of development, including the huge energy consumption of the smelting process (smelting 1 silicon power consumption of 400 ~ 500kW ˙h, silicon solar cell life expectancy of 25 years , The production process will cost silicon solar cells 7 to 8 years of power generation), the production cost is expensive (the main raw material is high purity silicon, each production 1MW scale silicon solar cell components need 17t high purity silicon). In addition, the crystalline silicon is an indirect bandgap semiconductor, the light absorption coefficient is low, the battery thickness generally need to reach more than 100m to absorb most of the sun, the processing of high damage rate, which led directly to the single crystal silicon battery product prices remain high.
Compared to single crystal silicon battery high energy consumption, high pollution refining, processing, polysilicon solar cell production costs are much lower. However, due to the existence of high density of polysilicon within the dislocation and defects, light conversion efficiency is low. At present, the small-area polysilicon battery developed by the laboratory has a light conversion efficiency of 20.3%, and the efficiency after industrialization is basically about 12%.
1.2 thin film solar cells
Thin film solar cell thickness can be reduced to several to tens of microns below the raw material consumption rate is low, the processing technology is simple, low energy consumption, low manufacturing cost, large area continuous production, in the photovoltaic field caused great concern. Thin-film batteries mainly include amorphous silicon thin-film batteries and other compounds thin film batteries.
The long-range disordered structure of amorphous silicon makes it a direct bandgap semiconductor, the light absorption coefficient is significantly improved, the corresponding battery thickness is greatly reduced, silicon raw material consumption is small, in the thin film solar photovoltaic products occupy a certain market share. However, after the prolonged use of amorphous silicon thin-film battery, the conversion efficiency is reduced, that is, the light-induced decay effect, photoelectric conversion efficiency is difficult to further improve the market process blocked.
Other compounds Thin film batteries are solar cells that are deposited on glass or flexible substrates. They are composed of GaAs, CdTe, CdS and CIGS, which are composed of p-n junctions. These compound thin film batteries are directly bandgap semiconductor materials, high light absorption coefficient, band gap width and solar energy spectrum matching is good, good photovoltaic characteristics. However, GaAs, CdS, CdTe series of batteries used in raw materials expensive, toxic, polluting the environment is serious, restricting its large-scale commercial applications.