Research On The Rapid Surface Texturization Of Monocrystalline Silicon

Photovoltaic power is an important part of solar energy utilization. It is a kind of clean and inexhaustible renewable green new energy. High efficiency and low cost are always constant pursuit for photovoltaic industry. At present, for efficient monocrystalline cells, the surface reflectivity is one of the important factors to influence the solar photoelectric conversion efficiency. The texture on solar cell surface can effectively reduce solar cell surface reflectivity. Currently, surface texturization of monocrystalline silicon for solar cells has been a mature technique, and chemical etching is the most often used system. But the longer texture time, usually for 30 min⁴0 min, is an universal existence problem. This thesis is focused on improving the texture production efficiency of monocrystalline silicon solar cell system, which is named rapid surface texturization. The target is to enhance the corrosion rate of the monocrystalline silicon in lye solution combined with the actual solar cell production system and the application process, to research the key factors and link of the texture to improve the silicon solar cell production efficiency, and to determine the specific production process scheme. Finally a uniformly distributed texture "pyramid" structure with low reflectivity which can be grown within 10 min¹5 min was achieved. The following items were studied in this thesis:First, on the basis of conventional texture technology, the concentration of the lye solution was improved to enhance the rate of silicon surface corrosion so that the texture can be formed in a shorter time. The effect of temperature, corrosion time, composition and remove of the surface damages on surface texturization in the NaOH/isopropyl alcohol (IPA) solution with shorter time was studied. Scanning electron microscope (SEM) was used to observation the surface texture topography, and spectral response tester was used to measure the surface reflectivity and the results were compared. Well-proportioned texturisation was obtained in 2.5%NaOH(in mass, the same below) and 10%IPA aqueous solution at 80℃with 15 min. The texturization was better when adding 3%Na₂SiO₃ in the solution, and the lowest reflectivity could be 9.5%. The work using other additives (1, 4-Cyclohexanediol, CHX and Sodium dodecylbenzene sulfonate, SDBS) instead of IPA was studied. It is found that CHX can increase the corrode rate, but the surface texture topography is uneven. SDBS is cheap but the corrode rate is slow. It costs longer time to obtain surface texturization. IPA is still considered to be the most suitable additive.Before texture making, the cleaning and removing of surface damage layer have better effect for conventional system. However, from experiments, although RCA cleaning makes texturization be more uniform and the reflectivity be smaller. The advantage is not clear. Meanwhile the cost and time consuming are increased. It has some environment problem. Removing surface damages before silicon texturing makes slow corrosion rate. It is difficult to form a complete pyramid structure texture in a short time. It can be concluded that the cleaning and removing of surface damages of silicon wafer before texturing is disadvantage to the productive efficiency.Tetramethylammonium hydroxide (TMAH)/IPA as the escharotic was used to texture monocrystalline silicon instead of traditional reagent NaOH/IPA, with the surfactant additive sodium dodecyl sulfate (SDS). In this work the concentration of TMAH, etching time and temperature in the solution, and the addition of SDS on the surface texturization of silicon was investigated. From the experimental studies, it is found that the texture with pyramid structure can be formed within 10 min in 2% (in mass, the same below) TMAH/5% IPA solution. In addition, the addition of 0.0004% SDS into the TMAH/IPA solution could reduce the pyramid size and the surface reflectivity of the silicon wafer.