Polycrystalline silicon solar cell production process

Written by Polycrystalline silicon solar cell

Monday, 06 October 2008 09:50

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As we all know, there are many advantages of using solar energy, photovoltaic power generation will provide the essential humanity of energy, but, to make solar power generation has a larger market, the overwhelming majority of consumers to accept and raise the photoelectric conversion efficiency of solar cells, Lower production costs should be our pursuit of the greatest goals. At present, solar cells from the international development process of their development trend can be seen as the single crystal silicon, polycrystalline silicon, ribbon silicon, thin film materials (including the microcrystalline silicon thin film, film-based compounds and dye film). From the industrial development, the focus has been to the single crystal polycrystalline direction, as the main reason; [1] could be the beginning and end of the supply of solar cells less and less material; [2] on the solar cell, a square substrate more Cost-effective, through the casting and direct access to the solidification method of polysilicon materials can be square; [3] polysilicon production process progress, automatic casting furnace each production cycle (50 hours) can produce over 200 kg Silicon ingot, grain size to achieve centimeter-level; [4] because of the past 10 years of single crystal silicon technology research and development soon, in which technology has been used in the production of polycrystalline silicon cells, for example, choose to launch corrosion knot back Field on the surface, corrosion suede, and body surface passivation, thin metal gate electrode, the use of screen printing technologies can reduce the width of the gate electrode to 50 microns to 15 microns high above, rapid thermal annealing technology for polycrystalline Silicon production process could significantly reduce the time to process a single heat time of one minute can be completed using the technology in the 100 square centimeters of silicon chip to make the conversion efficiency of the battery over 14%. It was reported that in 50 to 60 micron silicon substrate produced by the cells of more than 16% efficiency. The use of mechanical groove, screen printing technology in more than 100 square centimeters on the efficiency of grain more than 17%, non-mechanical groove in the same area on the efficiency of 16%, using buried gate structure, mechanical groove in the 130 square centimeters of the polycrystalline Cell efficiency 15.8 percent.

     The following two ways of polysilicon battery technology for discussion.

     Laboratory efficient battery technology

     Laboratory techniques are usually not taken into battery production costs and the possibility of large-scale production, the only study to achieve the most efficient ways and means to provide specific materials and processes can be achieved by the limit.

     On the absorption of light

     The light is absorbed:

    (1) reduce the reflective surface.

    (2) to change the battery in the light path of the body.

    (3) using the back of the reflector.

     The single crystal silicon, the application of the anisotropy of chemical corrosion in the way (100) produced on the surface of the pyramid-shaped pile structure, reduce the surface of optical reflection. But to depart from the crystalline silicon (100) surface, using the above methods can not be made uniform Flock, currently the following:

     Laser groove

     Laser groove of the way in the production of polycrystalline silicon surface inverted pyramid structure, in the spectral range 500 ~ 900nm, the reflection rate of 4 to 6 percent, double the production of the surface and by a very reflective film. In (100) single crystal silicon surface chemical production Flock reflectivity of 11%. Laser in the production of suede-smooth surface plating than double layer antireflection (ZnS/MgF2) short-circuit the battery to improve the current 4%, mainly long-wave (greater than the wavelength of 800nm) dipped into the battery. Flock laser production problems in etching, surface damage caused by the introduction of some of the impurities at the same time, through chemical treatment to remove the surface layer injury. The method is usually made by the solar cell short-circuit current high, but not open circuit voltage is too high, mainly due to increased cell surface area, improve the current rise complex.

     Chemical groove

Application mask (Si3N4 or SiO2) isotropic corrosion, etching solution for acid etching solution, but also for the high concentration of sodium hydroxide or potassium hydroxide solution, this method can not be formed by anisotropic etching to form the kind of Tip-like structure. It is reported that the method is formed to face down the 700-micron spectral range of 1030 to significantly reduce the role of reflection. However, mask-general in the formation of a high temperature, caused by polysilicon materials performance, particularly on the low quality of polycrystalline materials, reduce the minority carrier lifetime. The application of technology in 225cm2 made of polycrystalline silicon cell conversion efficiency of 16.4 percent. Mask layer can also be used to form the screen printing method.

     Reactive ion corrosion (RIE)

     This method is not a mask for the corrosion process, the formation of special low-reflectivity Flock, in 1000 to 450 microns wide spectrum reflectivity can be less than 2%. From the optical point of view, is an ideal method, but the problem is serious damage on the surface of silicon, the cell open circuit voltage and fill factor decreased.

     Produced by reflective film

     For efficient solar cells, the most common and most effective way is to reduce evaporation ZnS/MgF2 double-reflective film, the best depends on the thickness of the oxide layer below the thickness and surface characteristics of the battery, for example, the surface is smooth surface or suede , The reflection process by evaporation also Ta2O5, PECVD deposition Si3N3, and so on. ZnO films can also be used as anti-material cut.

     Metal Technology

     In the production of high-performance batteries, metal electrodes of batteries with the design parameters, such as the doping concentration on the surface, PN deep end, the metal material to match. Laboratory Battery general area is relatively small (area less than 4cm2), it needs fine-line metal gate (less than 10 microns), the general method used for lithography, electron beam evaporation, e-plating. Industrial production is also used in the plating process, but a combination of evaporation and lithography, does not belong to low-cost technology.

     Electron beam evaporation and electroplating

     In general, applications are plastic stripping process, the evaporation Ti / Pa / Ag multi-layer metal electrodes, it is necessary to reduce the metal electrode caused by the series resistance, often require relatively thick layer of metal (8 to 10 microns). The disadvantage is that electron beam evaporation caused by silicon surface / interface passivation layer damage, so increase the surface, technology, the use of short-term evaporated Ti / Pa layer, layer of silver in the evaporation process. Another problem is that silicon metal and a larger contact area, is bound to lead to increase the rate of minority carrier compound. Technology, used the tunnel junction contact method, in between silicon and metal into a thin layer of oxidation (generally a thickness of 20 microns or so) application of low work function metal (such as titanium, etc.) in the surface of silicon sensors A steady accumulation of e-layer (may also be the introduction of a fixed charge is to deepen anti-type). Another way is to open in the passivation layer on a small window (less than 2 microns), and then deposition of a wide metal gate line (usually 10 microns) to form a mushroom-like shaped electrode, the method used in the 4cm2 Mc-Si on the battery to reach 17.3 percent conversion efficiency. At present, the mechanical groove on the surface also used the Shallow angle (oblique) technology.

Last Updated on Thursday, 13 November 2008 04:27

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