Photovoltaic cells are the core modules of solar photovoltaic power generation systems, which largely determine the cost of system installations. In 1839, the French physical scientist E. Becquerel found that a “voltaic cell” composed of two pieces of metal immersed in a solution would generate additional “voltaic potential” when illuminated, resulting in a “photovoltaic effect” phenomenon, and thus a photovoltaic cell was made. The early photovoltaic cells had the problems of low energy conversion efficiency and high production cost. For the large-scale application of photovoltaic cells, scientists have been committed to solving these two problems. In the early 1950s, Bell Laboratories in the United States produced for the first time a practical monocrystalline silicon photovoltaic cell with a photoelectric conversion efficiency of 6%, opening a new era of photovoltaic power generation.
Solar photovoltaic cells are usually made of crystalline silicon or thin-film materials. The former is obtained by cutting, ingot casting or forging, and the latter is a thin film attached to a low-cost substrate. Crystalline silicon cells include monocrystalline silicon solar cells and polycrystalline silicon solar cells. The maximum laboratory conversion efficiency of monocrystalline silicon cells can reach 24.7%, and the maximum laboratory efficiency of polycrystalline silicon solar cells has exceeded 20%. At present, crystalline silicon is still the mainstream of solar photovoltaic cells. As represented by Professor Martin Green of the University of New South Wales in Australia, it is a world leader in the research of monocrystalline silicon solar cells.
Japan is the fastest growing country in the photovoltaic power generation industry, surpassing the United States in less than 10 years. In 2001, four of the top ten solar cell manufacturers in the world were Japan, namely Sharp, Kyoto Ceramics, Sanyo and Mitsubishi. In 2002, the global output of solar cells and photovoltaic modules was about 600MW, of which Japan accounted for 45%, the United States accounted for 25%, and Europe accounted for about 22%. Since 1995, solar cells have developed rapidly with an annual growth rate of 30%. By the end of 2004, the total output of solar cells in the world had exceeded 1200MW. China’s solar cell output continues to break through. By the end of 2005, China’s solar cell module production capacity had reached 400MW. However, the development of China’s photovoltaic market is relatively lagging. The annual installed capacity accounts for a relatively small proportion of the annual solar cell output. Most solar cells need to be exported abroad, and most of the raw material polysilicon is imported from abroad. Among the top ten solar cell manufacturers in the world in 2007 were Suntech in China, Motech Taiwan, and Yingli Baoding.
Although crystalline silicon solar cells account for more than 90% of the entire photovoltaic market, many solar cell manufacturers in various countries have regarded thin-film solar cells as the focus of future development. They have more development potential due to less materials, small quality, smooth appearance, and convenient installation.
The Solar Energy System Research Institute of Sun Yat-sen University installed 6 different types of solar cell grid-connected photovoltaic systems and analyzed the power generation data. In the case of relatively balanced energy output requirements, monocrystalline silicon and HIT modules have the best performance when the solar radiation is high, and they are suitable for use in areas with strong solar radiation and high-sky sky. Cadmium telluride has advantages in areas with high solar radiation, less clouds or cloudy areas. In areas with large changes in solar radiation and four distinct seasons, polysilicon and copper indium gallium selenium solar radiation have a greater impact and are not suitable for use. Amorphous silicon can only show its advantages in areas with low solar radiation and rainy areas.