Two key issues in developing solar cells are: improving conversion efficiency and reducing costs. Due to the low cost and convenient mass production of amorphous silicon thin film solar cells, they are generally valued and rapidly developed.
In fact, as early as the early 1970s, Carlson et al. began to develop amorphous silicon cells. In recent years, its research and development work has developed rapidly. At present, many companies in the world are producing such battery products.
Although amorphous silicon as a solar material is a good battery material, its optical band gap is 1.7 eV, which makes the material itself insensitive to the long-wavelength region of the solar radiation spectrum, thus limiting the amorphous silicon solar cell. Conversion efficiency. In addition, its photoelectric efficiency will be attenuated with the continuation of the illumination time, the so-called photo-degradation S-W effect, which makes the battery performance unstable. The solution to these problems is to prepare a tandem solar cell which is prepared by depositing one or more Pin subcells on a prepared p, i, n layer single junction solar cell. The key problems of the laminated solar cell to improve the conversion efficiency and solve the instability of the single-junction battery are as follows: 1. It puts together the materials of different forbidden band widths to improve the response range of the spectrum; The intensity of the electric field generated by the illumination does not change much, and the photo-generated carriers in the i-layer are extracted; the carrier generated by the bottom cell is about half of the single cell, and the photo-induced degradation effect is reduced; The batteries are connected in series.
There are many preparation methods for amorphous silicon thin film solar cells, including reactive sputtering, PECVD, LPCVD, etc. The reaction raw material gas is H2 diluted SiH4, the substrate is mainly glass and stainless steel, and the amorphous silicon is prepared. The single-cell battery and the tandem solar cell can be separately produced by the film through different battery processes. At present, research on amorphous silicon solar cells has made two major advances: the conversion efficiency of the first and third stacked-structure amorphous silicon solar cells reached 13%, setting a new record; the second-three-layer solar cell has an annual production capacity of 5MW. The maximum conversion efficiency of single-junction solar cells made by United Solar Corporation (VSSC) is 9.3%, and the maximum conversion efficiency of three-bandgap triple-stack cells is 13%. See Table 1
The above maximum conversion efficiency was obtained on a small area (0.25 cm2) battery. It has been reported in the literature that the conversion efficiency of single-junction amorphous silicon solar cells exceeds 12.5%. The Academia Sinica has adopted a series of new measures to achieve a conversion efficiency of 13.2% for amorphous silicon cells. There are not many researches on amorphous silicon thin-film batteries, especially laminated solar cells in China. Yan Xinhua of Nankai University uses industrial materials to prepare a-Si/ with an area of ​​20×20 cm2 and a conversion efficiency of 8.28%. a-Si laminated solar cell.
Amorphous silicon solar cells have great potential due to their high conversion efficiency, low cost and light weight. But at the same time, because of its low stability, it directly affects its practical application. If it can further solve the stability problem and improve the conversion rate, then the amorphous silicon solar cell is undoubtedly one of the main development products of solar cells.
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