At present, more than 95% of commercial solar cells are made of silicon. The advantages of silicon are mainly due to its abundant raw materials, mature process technology and no toxicity. The cost of silicon wafers accounts for 40% to 60% of the entire process, so material cost is an important issue. Both single-crystalline silicon (sc-Si) and multi-crystalline silicon (mc-Si) wafers are widely used, especially polycrystalline silicon wafers have great application potential due to their low cost advantages. Gradually increasing trend yang. The conversion efficiency of commercial polycrystalline silicon solar cells is generally 12% to 15%, and can be as high as 17% with more sophisticated solar cell designs. The potential of polysilicon is very high, and its efficiency has been increased to about 20% in the laboratory recently, which greatly increases its commercial viability.
The performance of polycrystalline silicon solar cells is mainly limited by the minority carrier recombination rate. During the crystallization process, the material will produce different defect structures, which determine and limit the efficiency of the cell. Generally speaking, dislocations and intra-grain defects, such as internal impurities, atomic clusters or precipitates, are the main reasons for the recombination of carriers; for relatively large grains on the centimeter scale, The grain boundaries become irrelevant.
Most of the cost of solar cells comes from the cost of substrates and manufacturing. Early solar cells are dominated by monocrystalline silicon. Because it can provide good conversion efficiency and use mature semiconductor manufacturing technology, it is generally used under non-cost considerations. In non-electric applications or artificial satellites or scientific experiments that require small area and high power generation, such as automobiles, etc. If it is to be commercialized and popularized, the cost of the product is an urgent problem that we need to solve, so the solar cell technology of polysilicon and amorphous silicon came into being.
There are two types of polycrystalline silicon solar cells: bulk polycrystalline silicon (bulk silicon) and thin-film polycrystalline silicon (thin-film pol e silicon). Because thin-film polycrystalline silicon has the advantages of reducing the dependence on wafers and reducing cost, so polycrystalline silicon thin-film solar cells are used. is an important trend yang. Because the thickness of the light absorbing layer of the solar cell is 2~3 times the thickness that the sunlight can absorb, and most of the electron-hole pairs act at the interface, it is only necessary to ensure that the grain size of the polysilicon film is larger than that of the film. thick, so that there are more minority carriers for effective power generation at the interface than short-lived carriers that flow into the grain boundaries, thereby suppressing the influence of grain boundaries, and then using an inexpensive substrate to make tandem silicon thin films (tandem thin films) -film) structure to form thin-film solar cells, and large-area solar cell modules can be fabricated.