Monocrystalline silicon solar cells
Among silicon-based solar cells, monocrystalline silicon solar cells boast the highest conversion efficiency and the most mature technology. High-performance monocrystalline silicon cells are built upon high-quality monocrystalline silicon materials and related mature processing techniques. Monocrystalline silicon cell manufacturing technology is nearly mature; techniques such as surface texturing, emitter passivation, and zoned doping are generally employed in cell fabrication. The main types of cells developed are planar monocrystalline silicon cells and grooved buried-grid monocrystalline silicon cells. Improving conversion efficiency primarily relies on the microstructure treatment of the monocrystalline silicon surface and zoned doping processes.
Monocrystalline silicon solar cells undoubtedly boast the highest conversion efficiency and still dominate in large-scale applications and industrial production. However, due to the high price of monocrystalline silicon materials and the corresponding complex cell manufacturing processes, the cost of monocrystalline silicon remains high, making it very difficult to significantly reduce its cost. To save on high-quality materials and find alternatives to monocrystalline silicon cells, thin-film solar cells have been developed, with polycrystalline silicon thin-film solar cells and amorphous silicon thin-film solar cells being typical examples.
Polycrystalline silicon thin-film solar cells
Typical crystalline silicon solar cells are fabricated on high-quality silicon wafers with a thickness of 350-450 μm, which are sawn from pulled or cast silicon ingots. Therefore, more silicon material is actually consumed. To save material, researchers began depositing polycrystalline silicon thin films on inexpensive substrates in the mid-1970s, but due to the small grain size of the grown silicon films, they failed to produce valuable solar cells. Research into obtaining thin films with large grain sizes has continued, and many methods have been proposed. Chemical vapor deposition (CVD) is the most common method for fabricating polycrystalline silicon thin-film solar cells, including low-pressure chemical vapor deposition (LPCVD) and plasma-enhanced chemical vapor deposition (PECVD). In addition, liquid phase epitaxy (LPPE) and sputtering deposition methods can also be used to fabricate polycrystalline silicon thin-film solar cells.
Polycrystalline silicon thin-film solar cells use far less silicon than monocrystalline silicon, do not suffer from efficiency degradation, and can potentially be fabricated on inexpensive substrates. Their cost is far lower than that of monocrystalline silicon cells, while their efficiency is higher than that of amorphous silicon thin-film cells. Therefore, polycrystalline silicon thin-film solar cells will soon dominate the solar cell market.
Amorphous silicon thin-film solar cells
Two key issues in developing solar cells are improving conversion efficiency and reducing cost. Due to their low cost and ease of mass production, amorphous silicon thin-film solar cells have received widespread attention and rapid development. There are many methods for preparing amorphous silicon thin-film solar cells, including reactive sputtering, PECVD, and LPCVD. The reactant gas is SiH4 diluted with H2, and the substrate is mainly glass or stainless steel sheet. The amorphous silicon thin film can be processed into single-junction cells and tandem solar cells through different cell manufacturing processes.
Amorphous silicon solar cells hold great potential due to their high conversion efficiency, low cost, and light weight. However, their low stability directly impacts their practical applications. If the stability and conversion efficiency issues can be further resolved, amorphous silicon solar cells will undoubtedly become one of the main development products in the solar cell industry.
