Solar Cell Types
The most commonly used semiconductor materials for the Special materials are used for the construction of photovoltaic cells. These materials are called construction of PV cells is Silicon. Several forms of Silicon are used for the construction viz:
Silicon solar cells can differ in their crystal structure. In monocrystalline solar cells, the silicon is in the form of a single crystal with a uniform crystal lattice structure. This homogeneous form of the crystal permits them to generate more energy from sunlight than crystals with a non-uniform crystal structure. Monocrystalline silicon is, however, relatively expensive to manufacture, and more energy has to be expended in the fabrication of these solar cells. This in turn affects the 'energy return time'.
The polycrystalline variant is different. Here, the silicon consists of numerous small individual crystals. The solar cells are cheaper to manufacture and the energy return time is considerably shorter and their efficiency is somewhat less than the monocrystalline
Amorphous silicon can absorb 40 times more solar radiation than single-crystal silicon. This is one of the main reasons why amorphous silicon can reduce the cost of photovoltaics. Amorphous silicon can be coated on low-cost substrates such as plastics and glass. This makes amorphous silicon ideal for building-integrated photovoltaic products.
Polycrystalline thin films:
Numerous thin-film technologies are currently being developed to decrease the amount of light absorbing material required to produce solar cells. This could lead to a reduction in the processing costs; however it could also lead to a reduction in the energy conversion efficiency.
Copper Indium Diselenide
Copper indium diselenide or CIS for short, has an extremely high absorptivity. This means that 99% of the light illuminated on CIS will be consumed in the first micrometer of the material. The addition of a small amount of gallium will improve the efficiency of the photovoltaic device. This is commonly referred to as copper indium gallium diselenide or CIGS photovoltaic cell.
Cadmium telluride or CdTe is another well-known polycrystalline thin-film material. Similar to copper indium diselenide, CdTe also has a very high absorptivity and can be produced using low-cost techniques. The properties of CdTe can be altered by the addition of alloying elements such as mercury and zinc.
Basic Factors on which the performance of the different types of Solar cell materials depends upon are:
The crystallinity of a material indicates how perfectly ordered the atoms are in the crystal structure. Silicon, as well as other solar cell semiconductor materials, can come in various forms: single-crystalline, multicrystalline, polycrystalline, or amorphous. In a single-crystal material, the atoms making up the framework of the crystal are repeated in a very regular, orderly manner from layer to layer. In contrast, in a material composed of numerous smaller crystals, the orderly arrangement is disrupted moving from one crystal to another. One classification scheme for silicon uses approximate crystal size and also includes the methods typically used to grow or deposit such material.
he absorption coefficient of a material indicates how far light having a specific wavelength (or energy) can penetrate the material before being absorbed. A small absorption coefficient means that light is not readily absorbed by the material. Again, the absorption coefficient of a solar cell depends on two factors: the material making up the cell, and the wavelength or energy of the light being absorbed. Solar cell material has an abrupt edge in its absorption coefficient. The reason is that light whose energy is below the material's bandgap cannot free an electron. And so, it isn't absorbed.
The bandgap of a semiconductor material is an amount of energy. Specifically, it's the minimum energy needed to move an electron from its bound state within an atom to a free state. This free state is where the electron can be involved in conduction. The lower energy level of a semiconductor is called the "valence band." And the higher energy level where an electron is free to roam is called the "conduction band." The bandgap (often symbolized by Eg) is the energy difference between the conduction band and valence band.