Classification of photovoltaic cells
Silicon solar cells can be classified into monocrystalline silicon, polycrystalline silicon, and amorphous silicon solar cells. Photovoltaic cells can be further classified into several types based on their variety:
1. Monocrystalline silicon photovoltaic cells
Monocrystalline silicon photovoltaic cells are among the earliest developed, most efficient, and most widely produced types of photovoltaic cells. In my country, the average conversion efficiency of monocrystalline silicon photovoltaic cells has reached 19%, while the highest recorded conversion efficiency in the laboratory exceeds 24.7%. These photovoltaic cells typically use high-purity monocrystalline silicon rods as raw materials, requiring a purity of 99.9999%.
2. Polycrystalline silicon photovoltaic cells
Polycrystalline silicon photovoltaic cells are photovoltaic cells that use polycrystalline silicon material as their substrate. Because polycrystalline silicon is mostly produced through casting instead of the pulling process used for monocrystalline silicon, production time is shortened and manufacturing costs are significantly reduced. Furthermore, since monocrystalline silicon rods are cylindrical, photovoltaic cells made from them are also discs, resulting in lower planar utilization when assembled into photovoltaic modules. Compared to monocrystalline silicon photovoltaic cells, polycrystalline silicon photovoltaic cells exhibit certain competitive advantages.
3. Amorphous silicon photovoltaic cells
Amorphous silicon photovoltaic cells are a new type of thin-film battery made from amorphous silicon. Amorphous silicon is a semiconductor with an amorphous crystal structure. Photovoltaic cells made from it are only 1 micrometer thick, equivalent to 1/300th the thickness of monocrystalline silicon photovoltaic cells. Its manufacturing process is greatly simplified compared to monocrystalline and polycrystalline silicon, consuming less silicon material and significantly reducing unit power consumption.
4. Copper indium selenide photovoltaic cells
Copper indium selenide (CIGS) photovoltaic cells are semiconductor thin films deposited on glass or other inexpensive substrates using copper, indium, and selenium as the basic materials. Because CIGS cells have excellent light absorption performance, their film thickness is only about 1/100 that of monocrystalline silicon photovoltaic cells.
5. Gallium arsenide photovoltaic cells
Gallium arsenide (GaAs) photovoltaic cells are a type of III-V compound semiconductor photovoltaic cell. Compared to silicon photovoltaic cells, GaAs photovoltaic cells have a higher photoelectric conversion efficiency. The theoretical efficiency of silicon photovoltaic cells is 23%, while the conversion efficiency of single-junction GaAs photovoltaic cells has reached 27%. They can be fabricated into thin-film and ultra-thin solar cells, absorbing 95% of sunlight. GaAs photovoltaic cells only require a thickness of 5-10 μm, while silicon photovoltaic cells require a thickness greater than 150 μm.
6. Cadmium telluride photovoltaic cells
Cadmium telluride (CdTe) is a compound semiconductor with a band gap optimally suited for photoelectric energy conversion. Photovoltaic cells made from this semiconductor have high theoretical conversion efficiencies, with the highest practically achieved efficiency reaching 16.5%. CdTe photovoltaic cells are typically manufactured on a glass substrate. The first layer on the glass is a transparent electrode, followed by thin layers of cadmium sulfide, cadmium telluride, and a back electrode. The back electrode can be a carbon paste or a thin metal layer. Many deposition techniques exist for CdTe, such as electrochemical deposition, near-space sublimation, close-range vapor transport, physical vapor deposition, screen printing, and spraying. The thickness of the CdTe layer is typically 1.5-3 μm, and a thickness of 1.5 μm is sufficient for CdTe's light absorption.
7. Polymer photovoltaic cells
Polymer photovoltaic cells utilize the different redox potentials of different redox polymers to create a unidirectional conductive device similar to an inorganic PN junction by multi-layering on the surface of a conductive material.
