Solar cells are mostly made of semiconductor materials. So far, they have been developed in various types and forms. Various methods can be used to classify solar cells, such as different classifications according to different structures, different classifications according to different materials, different classifications according to different uses, and different classifications according to different working methods.
(1) Classified according to structure. According to different structures, solar cells can be divided into the following categories:
① Homojunction solar cells. The PN junction or gradient junction formed by the same semiconductor material is called a homojunction. Solar cells made of homogenous structures are called homojunction solar cells, such as silicon solar cells, gallium arsenide solar cells, etc..
Heterojunction solar cells. The junction formed by two semiconductor materials with different band gap widths is called heterojunction, and solar cells made of heterostructure are called heterojunction solar cells, such as tin oxide/silicon solar cells, cuprous sulfide/cadmium sulfide solar cells, gallium arsenide/silicon solar cells, etc. If the lattice structure of the two heterogeneous materials is similar and the lattice matching at the interface is better, it is called a heterogeneous solar cell, such as aluminum gallium arsenide/gallium arsenide heterogeneous solar cell.
③ Schottky solar cells. Solar cells that use the Schottky barrier at the metal-semiconductor interface are also called MS solar cells, such as platinum/silicon Schottky solar cells, aluminum/silicon Schottky solar cells, and so on. The principle is based on the Schottky effect of rectifying contact under certain conditions when metal-semiconductor contact is made. At present, it has developed into a solar cell made of a metal-oxide-semiconductor (MOS) structure and a solar cell made of a metal-insulator-semiconductor (MIS) structure. These are collectively referred to as conductor-insulator-semiconductor (CIS) solar cells.
④ Multi-junction solar cells. Solar cells formed by multiple PN junctions, also known as composite junction solar cells, include vertical multi-junction solar cells and horizontal multi-junction solar cells.
⑤ Liquid junction solar cell. Solar cells composed of semiconductors immersed in electrolyte are also called photoelectrochemical cells.
(2) Classified by material. According to different materials, solar cells can be divided into the following categories:
①Silicon solar cells. Refers to solar cells using silicon as the base material, such as monocrystalline silicon solar cells and polycrystalline silicon solar cells. Polycrystalline silicon solar cells include sheet polycrystalline silicon solar cells, ingot polycrystalline silicon solar cells, simple polycrystalline silicon solar cells, spherical polycrystalline silicon solar cells, and so on.
② Compound semiconductor solar cells. Refers to solar cells made of compound semiconductor materials with semiconductor characteristics composed of two or more elements, such as cadmium sulfide solar cells, gallium arsenide solar cells, cadmium telluride solar cells, indium copper selenide solar cells, indium phosphide solar cells, etc. Compound semiconductors mainly include:
·Crystal inorganic compounds, such as III-V compound semiconductor gallium arsenide, gallium phosphide, indium phosphide, indium antimonide, etc., II-I compound semiconductor cadmium sulfide, zinc sulfide, etc. and their solid solutions (such as aluminum arsenide, gallium arsenic phosphorus, etc.).
·Amorphous inorganic compounds, such as glass semiconductors.
·Organic compounds, such as organic semiconductors.
·Oxide semiconductors, such as MnO, Cr2O3, FeO, Fe2O3, Cu2O, etc.
③ Organic semiconductor solar cells. Refers to a solar cell made of a semiconductor material that contains a certain number of carbon-carbon bonds and has an electrical conductivity between metal and insulator. Organic semiconductors can be divided into 3 categories:
·Molecular crystals, such as naphthalene, organic anthracene, perylene, copper phthalocyanine, etc.
·Charge transfer complexes, such as arene-halogen complexes, arene-metal halides, etc.
④ Thin-film solar cells. Refers to solar cells made of simple elements, inorganic compounds, or organic materials that use thin films as the base material. Generally, the thickness of the film layer that can be independently formed without a substrate is taken as the approximate standard of the film thickness, and the thickness is specified to be about 1~2um. These films are usually made by methods such as glow discharge, chemical vapor deposition, sputtering, and vacuum evaporation. At present, there are mainly amorphous silicon thin film solar cells, polycrystalline silicon thin film solar cells, compound semiconductor thin film solar cells, nanocrystalline thin film solar cells, and microcrystalline silicon thin film solar cells. Amorphous silicon thin-film solar cells refer to solar cells made of amorphous silicon materials and their alloys, also known as amorphous silicon thin-film solar cells, a-Si solar cells for short. At present, there are mainly PiN (NiP) amorphous silicon thin film solar cells, integrated amorphous silicon thin film solar cells, laminated (cascade) amorphous silicon thin film solar cells, etc.
Classified according to the structure of solar cells, its physical meaning is relatively clear, so China’s national standards use it as the basis for the naming method of solar cells. In addition, solar cells can be divided into two categories: space solar cells and ground solar cells. Ground-use solar cells can be divided into two types: solar cells for power supplies and solar cells for consumer products. The technical and economic requirements for solar cells vary by application: the main requirements for space solar cells are high radiation resistance, high photoelectric conversion efficiency, excellent power area ratio and power quality ratio; the main requirements of solar cells for ground power supply are high photoelectric conversion efficiency, sturdiness and reliability, long life, low cost, etc.; the main requirements for solar cells for ground consumer goods are thinness, lightness, beauty and durability.