Polycrystalline Silicon Solar Cell Production Process
Author: Source: Datetime: 2016-09-22 11:50:04
Large-scale production of polycrystalline silicon solar power battery are widely used in the solar power portable generator which can be used for portable power bank,the front electrode metal diffusion source and back-contact electrode, antireflection film,etc. With the improvement of the level of technology and the screen material,screen printing process in the production of solar cells will be more widely used.
1. Formed-emitting Region
PN junction is formed by screen printing, instead of the conventional tube furnace diffusion process. Usually printed on the front of phosphorus in the polycrystalline silicon paste, metal paste containing aluminum reverse printing. After printing, the diffusion can be completed in a belt furnace (usually at a temperature of 900 degrees), so, printing, drying, diffusion can be formed continuous production. Emitter region formed by screen printing technology diffusion surface is generally relatively high concentration, the surface of solar powered portable generator carrier recombination larger, in order to overcome this drawback, the process uses the following selection technology emitting region, so that the conversion efficiency of the battery to give further improvement.
2. Select Emitting Region Process
In the diffusion process of polycrystalline silicon cells, select the area of technology is divided into launching localized corrosion or two-step diffusion method. Localized corrosion is a dry method (such as reactive ion etching) method or chemical corrosion, heavy diffusion layer region between the metal electrodes etched. Initially, Solarex reactive ion etching method applied in the same device, the first reaction with a large etching portable solar power generator off heavily doped layer between the metal electrodes, lifePo4 batteries and then a small power deposition layer of silicon nitride film, the antireflection film and play the dual role of cell surface passivation. Make a conversion efficiency of more than 13% of the battery in the 100cm2 polycrystalline. In the same area, the application of two diffusion method, the case of the absence of mechanical suede conversion efficiency of 16%.
3. Forming a Back Surface Field
PN junction is usually in the back of the mesh belt furnace after thermal annealing A slurry is formed by screen printing and, at the same time the process of forming the back surface of the junction, impurities in the polysilicon has good suction effect, aluminum gettering process in general high-temperature zone is complete, the measurement results show that the gettering effect can decrease the minority carrier lifetime of polysilicon portable solar power generator front-temperature processes caused restored. Good back surface field can significantly increase the open-circuit voltage of the battery.
4.Screen printing Metal Electrode
In the large-scale production for portable solar power generator, the screen printing process compared with vacuum evaporation, metal plating and other processes, has more advantages in the current process, the front printed material generally choose silver-containing slurry, mainly due to a good silver conductivity, weldability and low diffusion properties in silicon. Conductivity metal layer by screen printing, annealing the formed slurry depends on the chemical composition, the content of the vitreous, the coarsening of the screen, and sintering conditions of the screen plate thickness. First eighty years, screen printing has some drawbacks, ⅰ) gate line width as large, typically greater than 150 microns; ii) large shading caused, battery low fill factor; iii) is not suitable for surface passivation, the surface of the main high concentration diffusion, solar powered portable generator or else contact resistance is large. Advanced methods currently used may qualify wide screen printing 50 micron grid lines, more than 15 microns thickness, sheet resistance of 2.5 - 4mΩ, this parameter can meet the requirements of high-performance batteries. It was on the 15x15 cm Mc-Si on the screen-printed electrodes and electrodes made by solar evaporation were compared, the parameters are almost no gaps.
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