Solar cells and their classification

A solar cell is a device that uses the photovoltaic effect to convert light energy into electrical energy, also known as photovoltaic device. The phenomenon that matter absorbs light energy to generate electromotive force is called photovoltaic effect. This phenomenon occurs in both liquid and solid substances. However, only in solids, especially in semi-heterosomes. Only with higher energy conversion efficiency, people often refer to solar cells as semiconductor solar cells.

Solar cells are mostly made of semiconductor materials and have been developed so far. There have been many types of purple, in various forms.

(1) Classification by structure

According to different structures, solar cells can be divided into the following five categories.

①Homojunction solar cells Homojunction solar cells are solar cells in which one or more P-N junctions are composed of the same semiconductor material. Such as silicon solar cells, arsenic rubber solar cells and so on.

②Heterojunction solar cell Heterojunction solar cell is a solar cell that uses two semiconductor materials with different forbidden band widths to form a hetero P-N junction at the interface, such as tin oxide/silicon solar cells, cuprous sulfide solar cells If the lattice structure of the two heterogeneous materials is similar, and the quality at the interface is well matched, then it is called a heteroplane solar cell, such as AlGaAs/GaAs heterogeneity and solar cells battery etc.

③Schottky junction solar cell Schottky junction solar cell is a “Schottky potential hybrid” solar cell composed of metal and semiconductor contacts, also called MS solar cell. The principle is based on the self-Terky effect of rectifying contact when metal-semiconductor contacts under certain conditions. At present, cells with this structure have been developed into metal oxide semiconductor solar cells. Namely MOS solar cells: metal insulator-semiconductor solar cells, namely MIS solar cells, such as aluminum/silicon Schottky junction solar cells, aluminum/silicon Schottky base station solar cells, etc.

④Multi-junction solar cells Solar cells formed by multiple P-N junctions are called multi-junction solar cells, also known as compound junction solar cells, and are divided into vertical multi-junction solar cells and horizontal multi-junction solar cells.

⑥ Liquid junction solar cells Solar cells composed of semiconductors immersed in an electrolyte are called liquid junction solar cells, also known as photoelectrochemical cells.
According to the structure of solar cells, the physical meaning is relatively clear, so it has been adopted by the country as the basis for the naming method of solar cells.

(2) Classification by material

Solar cells can be divided into the following categories according to different materials.

①Silicon solar cell This kind of cell is a solar cell with silicon as the base material, such as single-product silicon solar cell, multi-product male solar cell, amorphous silicon solar cell, etc. To make multi-product silicon solar cells, solar-grade silicon with a low purity can be used. Polysilicon materials also include ribbon silicon, cast silicon, thin-film multi-product silicon, etc. The solar cells made from them have two types: thin-film and sheet-like.

②Compound semiconductor solar cell This kind of solar cell refers to a solar cell made of compound materials with semiconductor properties composed of two or more elements. Such solar cells can also be divided into four categories: crystalline inorganic compounds, amorphous inorganic compounds and organic compounds, and oxide semiconductors. The former includes III-V group compound semiconductors gallium arsenide, gallium phosphide, indium phosphide, indium phosphide, etc., II-IV group compound semiconductors cadmium sulfide, zinc sulfide, etc., as well as their solid solutions (such as aluminum arsenic, arsenic phosphorus, etc.). etc.); the latter such as glass semiconductors, organic semiconductors, oxide semiconductors (such as MnO, Cr2O3, FeO, Fe2O3, Cu2O, etc.).

③Organic semiconductor solar cells refer to solar cells made of organic semiconductor materials that contain a certain number of carbon-carbon bonds and have a conductivity between metals and insulators. There are molecular crystals such as naphthalene, anthracene, and pyrene, and aromatic hydrocarbon-halogen complexes , arene-metal halide and other charge transfer complexes and polymers.

(3) Classification by shape

solar cells are divided into two types: bulk and thin-film solar cells according to the thickness of the semiconductor. Bulk solar cells refer to bulk crystals made of monocrystalline silicon and polycrystalline silicon, which are then processed into flakes as flake semiconductors for solar cells. Bulk crystalline silicon solar cells are widely used in electricity. Among the bulk crystals, the semiconductors of III-V compounds such as GaAs and InP are amorphous silicon systems, which attract attention with the conversion efficiency expected to reach 30% to 40%. The substrate and processing costs of such materials are very high, so the current focus is on aerospace and concentrator cells.

A thin-film solar cell refers to a solar cell with a semiconductor layer thickness of 50 μm or less. Thin-film solar cells include silicon-based thin-film solar cells, Ⅱ-VI compound thin-film solar cells and chalcopyrite-based solar cells. The representative of silicon-based thin-film solar cells is amorphous silicon (a-Si) solar cells, which have been mass-produced in China and abroad. The thickness of amorphous silicon solar cells is only 0.3 μm. In addition, while making further use of the advantages of amorphous silicon, it is also making up for its shortcomings. Therefore, it is expected that the conversion efficiency of amorphous silicon solar cells will be greatly improved by using thin-film solar cells such as polysilicon and microcrystalline silicon. High expectations are placed on multi-junction thin-film solar cells combined with polysilicon stacks. In the compound thin film system, small-scale Cu(InGa)Se2(CIGS) solar cells are also being sold. In addition, large-area modules made of CdTe thin-film solar cells have also entered the residential sector.

There are also organic materials and dye-sensitized batteries that will be new materials in the future.