Silicon-based thin film technology is a technology that uses silane and other gases as raw materials and uses low-temperature plasma enhanced chemical vapor deposition to produce silicon-based thin-film batteries on glass substrates. The band gap difference of different silicon-based thin film materials can be used to prepare multi-layered cells with different band gaps to achieve a larger range of solar light absorption.
(1) Amorphous silicon thin film solar cells.
The basic feature of amorphous silicon is the short-range order of atoms and the long-range disorder. Single crystal silicon is anisotropic, polycrystalline silicon, microcrystalline silicon and nano silicon are multi-directional, and amorphous silicon is isotropic. The thickness of crystalline silicon is generally 200~300μm, but the absorption layer of crystalline silicon only needs about 25μm, which is enough to absorb a large amount of solar energy. Amorphous silicon has a higher potential energy than crystalline silicon and is in a metastable state. Amorphous silicon can be converted into polycrystalline silicon, microcrystalline silicon and nano silicon through appropriate heat treatment. The density, conductivity and energy gap can be adjusted by changing the alloy composition and doping composition. Compared with crystalline silicon, the material and manufacturing cost are low. In the visible light range, the absorption coefficient is much higher than that of crystalline silicon. The thickness is less than 1μm to fully absorb light energy, which is less than 1% of the equivalent thickness of crystalline silicon. The manufacturing process is carried out at low temperature. , The deposition temperature is only 100~300℃, with high production efficiency, low energy consumption and good working conditions. But the disadvantage is that its photoelectric conversion efficiency can only reach 13% in the laboratory, and it can only reach 10% in actual production.
(2) Polycrystalline silicon thin film solar cells.
Polycrystalline silicon film is a solar cell material that not only maintains the advantages of crystalline silicon and amorphous silicon, but also overcomes the weaknesses of amorphous silicon. Like amorphous silicon, polysilicon films can be deposited on the surface of various inexpensive materials to form polysilicon films. The process is simple, the cost is low, the light absorption rate is high, and there is no light attenuation. According to the size of its crystal grains, it is called nano-silicon (nc-Si) at about 10nm, and micro-silicon (μc-Si) at 10~30nm. The other is composed of some fine polysilicon embedded in amorphous silicon. These polycrystalline silicon thin films alone or in combination with amorphous silicon can be made into a variety of new thin-film solar cells. The weakness compared with crystalline silicon is that it has low doping rate, low photoelectric conversion rate and light attenuation.
(3) The structure of the silicon thin film cell.
Figure 1 shows the cell structure of polysilicon and amorphous silicon. The picture (a) shows the structure of a polycrystalline silicon thin film cell. Its structure is similar to that of crystalline silicon, except that the silicon material is changed from crystalline silicon to a polycrystalline silicon thin film. The substrate can be glass, low-purity polycrystalline silicon or SiC. A PN junction is made on this substrate, and then an anti-reflection film and a metal electrode are prepared to finally become a polycrystalline silicon thin-film solar cell. (B) It is the cell and energy band structure of the amorphous silicon thin film cell. The structure of the amorphous silicon cell is different from the PN structure in crystalline silicon, but the PIN structure. The intrinsic absorption layer I must be added between the PN to form the PIN structure. The built-in electric field formed by the PI junction and the IN junction crosses the I intrinsic layer to generate a photovoltaic voltage. The figure also shows the band structure of PIN. The I intrinsic absorption layer is also called the photosensitive region, which is the source of photovoltaic current generation. (C) It is a laminated amorphous silicon thin-film cell structure, that is, a laminated cell is formed by superimposing multiple PIN batteries. The efficiency and stability are greatly improved, and the production cost increases less, but too much interface will bring Certain influence.