In order to find alternatives to monocrystalline silicon cells, in addition to the development of polysilicon, amorphous silicon thin-film solar cells, they have continued to develop solar cells with Other materials. Among them, there are mainly III-V gallium arsenide compounds, cadmium sulfide, cadmium sulfide, and copper gallium selenide thin film batteries. Among the above batteries, although the efficiency of cadmium sulfide and cadmium telluride polycrystalline thin film batteries is higher than that of amorphous silicon thin film solar cells, the cost is lower than that of single crystal silicon batteries, and it is also easy to produce on a large scale. However, since cadmium is extremely toxic, it will Serious pollution to the environment, therefore, is not the ideal replacement for crystalline silicon solar cells, gallium arsenide III-V compounds and copper indium selenide thin-film batteries because of its high conversion efficiency has been the people's attention. GaAs is a III-V compound semiconductor material, and its energy gap is 1.4 eV, which is exactly the value of high-absorption solar light. Therefore, it is an ideal battery material. The preparation of III-V compound thin-film batteries such as GaAs mainly uses MOVPE and LPE technologies. The MOVPE method for preparing GaAs thin-film batteries is affected by various parameters such as substrate dislocation, reaction pressure, III-V ratio, and total flow rate. In addition to GaAs, other III-V compounds such as Gasb, GaInP and other battery materials have also been developed. In 1998, the conversion efficiency of GaAs solar cells made by the Solar System Research Institute in Freiburg, Germany was 24.2%, which was recorded in Europe.
The GaInP cell conversion efficiency for the first time was 14.7%. In addition, the Institute also uses a stacked structure to fabricate GaAs, Gasb cells. The cell is a stack of two separate cells. GaAs is used as the upper cell and the lower cell is Gasb. The resulting cell efficiency is 31.1%. .
Copper Indium Selenide CuInSe2 referred to as CIC. The CIS material can be reduced to 1. leV, suitable for photoelectric conversion of sunlight, in addition, CIS thin film solar cells do not suffer from light-induced degradation. Therefore, CIS is also attracting attention as a material for high conversion efficiency thin-film solar cells.
The preparation of CIS battery films includes vacuum evaporation and selenization. In the vacuum evaporation method, copper, indium, and selenium are vapor-deposited using respective evaporation sources, and the selenization method uses selenization of the H2Se laminated film, but this method is difficult to obtain a CIS having a uniform composition. CIS thin-film batteries have grown from the initial 8% conversion efficiency in the 1980s to the current level of about 15%. The erbium-doped CIS battery developed by Matsushita Electric Industrial Co., Ltd. has a photoelectric conversion efficiency of 15.3% (an area of ​​1cm2). In 1995, the United States Renewable Energy Research Institute developed a conversion efficiency of 17. l% of CIS solar cells, which is by far the highest conversion efficiency of the battery in the world. It is expected that the conversion efficiency of CIS cells will reach 20% by 2000, which is equivalent to polysilicon solar cells.
As a semiconductor material for solar cells, CIS has the advantages of low cost, good performance and simple process, and will become an important direction for the development of solar cells in the future. The only problem is the source of the material. Since indium and selenium are relatively rare elements, the development of such batteries is bound to be limited.
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