Among compound semiconductor solar battery, CaAs, InP, CulnSe2 and CdTe solar cells are currently researched and applied more. Since compound semiconductors are more or less toxic and are likely to cause environmental pollution, their yields are small, and they are often used in special occasions. The multi-compound thin film solar cell materials are inorganbatteryic salts, which mainly include gallium arsenide III-V group compounds, cadmium sulfide and copper indium selenide thin film batteries.
1) GaAs solar cells
The photoelectric conversion efficiency of gallium arsenide (GaAs) III-V compound cells can reach 28%. The GaAs compound material has a very ideal optical band gap, high absorption efficiency, strong radiation resistance, and is insensitive to heat, and is suitable for the manufacture of high-efficiency single-junction cells. However, the high price of GaAs materials limits the popularity of GaAs cells to a large extent. For general aerospace, the photoelectric conversion efficiency of solar cells is 18% to 19.5%. At present, GaAs solar cells are mostly prepared by liquid phase epitaxy or metal organic chemical vapor deposition (MOCVD) technology, so the cost is high and the yield is limited. Reducing cost and improving production efficiency have become the focus of research.
Now, the preparation technology of silicon single wafer is mature and the cost is low. Therefore, it is a promising way to use the silicon wafer as the substrate to manufacture GaAs solar cells by heteroepitaxial method with MOCVD technology to reduce the cost of GaAs solar cells. At present, the photoelectric conversion efficiency of this solar cell has reached more than 20%. However, the lattice constants of GaAs and Si crystals are quite different. During heteroepitaxial growth, the lattice mismatch of the epitaxial layer is serious, and it is difficult to obtain a high-quality epitaxial layer. For this reason, a layer of Ge crystal whose lattice constant is less different from that of GaAs is often grown on the silicon substrate.
As the transition layer, and then grow the GaAs epitaxial layer, the heteroepitaxial cell of this Si/Ge/GaAs structure is under continuous development. By controlling the thickness of each layer and changing the structure appropriately, the photon energy of various wavelengths in sunlight can be effectively utilized. At present, the photoelectric conversion efficiency of multi-layer solar cells with GaAs as the substrate is close to 40%.
2) Phosphate steel solar cells
Phosphate steel solar cells have particularly good radiation resistance, so they are valued in aerospace applications. At present, the photoelectric conversion efficiency of this battery has reached 17% to 19%.
3) Nanocrystalline chemical solar cells
Nanocrystalline chemical solar cell is a new type of solar cell, which is still under development, among which nanocrystalline TiO2 solar cell has attracted much attention. The photoelectric conversion efficiency of nanocrystalline TiO2 solar cells is above 10%, the production cost is 1/5~1/10 of that of silicon solar cells, and the service life can reach more than 20 years. However, the research and development of such batteries has just started, and it is estimated that they will gradually enter the market soon.
4) Polymer multilayer modified electrode solar cells
The raw material of the polymer multi-layer modified electrode solar cell is an organic material, which has good flexibility, easy fabrication, wide material sources and low cost. But the performance and lifespan are far inferior to silicon cells, but they have the potential to provide cheap electricity. This research has just started, neither the service life nor the photoelectric conversion efficiency of the battery can be compared with the characteristics of inorganic materials.
Especially compared to silicon batteries. Whether it can be developed into a product with practical significance remains to be further studied and explored.
The development trend of solar cells
As the materials of solar cells, III-V compounds are prepared from rare elements. Although the photoelectric conversion efficiency of solar cells made of them is very high, from the perspective of material sources, such solar cells will not be able to dominate in the future. The research on the other two types of solar cells (nanocrystalline solar cells and polymer modified electrode solar cells) has just started, the technology is not very mature, and the conversion efficiency is still relatively low. These two types of cells are still in the exploratory stage and cannot be replaced in a short time. Silicon solar cells. Therefore, from the perspective of conversion efficiency and material sources, the focus of future development is still on silicon solar cells, especially polysilicon and amorphous silicon thin-film cells. Due to the high conversion efficiency and relatively low cost of polycrystalline silicon and amorphous silicon thin film cells, they will eventually replace monocrystalline silicon cells and become the dominant product in the market. Improving the conversion efficiency and reducing the cost are two main factors considered in the preparation of solar cells. For the current silicon-based solar cells, it is difficult to further improve the conversion efficiency. Therefore, in addition to continuing to develop new solar cell materials, the focus of future research should focus on how to reduce costs. Existing high-conversion-efficiency solar cells are fabricated on high-quality silicon wafers, which is the most expensive part of making silicon solar cells. Therefore, it is particularly important to reduce the cost of the substrate while ensuring that the conversion efficiency is still high, and it is also an urgent problem to be solved in the development of solar cells in the future. Recently, some technologies have been used abroad to prepare silicon strips as substrates for polycrystalline silicon thin-film solar cells to reduce costs.
purpose, the effect is still relatively ideal.