Study Of Monocrystallion Sillicon Texturization For Solar Cells

Reducing the cost and increasing the efficiencies of monocrystallion silicon solar cells have been hot topics since the first device prepared early. From the development history of monocrystallion silicon solar cells it is seen that light trapping structure has gained much attentions. A perfect light trapping structure increases the absorption of light most to achieve a high efficieny. Texturization is the easiest and most effective light trapping structure. It not only reduces the surface reflectivity, but also tilts incident lights to increase the optical path.Anisotropic texturization of monocrystalline has been known for years. The aqueous alkaline solution, such as NaOH with isopropyl alcohol (IPA) as a surface-active additive, was widely used for texturing. IPA is essential in the approach in respect that it improves the wettability of the wafer surface, results in the removal of hydrogen bubbles adhering on the wafer surface which prevent the continuing texturization. But IPA is volatile especially in a heated etching bath, it must be constantly added to the solution to compensate the lost due to volatilization. The cost of IPA plays a dominant role in the cost reduction of current industrial texturing process based on alkaline solution. In order to reduce the texturization cost people have been looking for new etching solutions and methods for years.In this paper, texturization of (100)-oriented monocrystalline silicon wafers has been studied, especially metal grids-based texturization. The diffuse reflectance testing system, AFM and SEM are used to characterize the textured silicon.NaOH solutions with metal grids are used to etch monocrystalline silicon wafers. A textured silicon with average reflectance of 15.8% is obtained. In spite of no surface-active additive is needed in this method, however the reflectance of textured silicon is not as low as that obtained by conventional texturization process.In order to reduce reflectance, a metal grids-based texturization approach of monocrystalline silicon wafers with sodium carbonate solution is proposed. Using this etching process a low reflectance of silicon surface is obtained for solar cells and the cost is lower than conventional texturization process. In the present work metal grids with suitable openings are used to capture hydrogen bubbles and remove them from the silicon surface, which are created due to the texturing reaction and sticked on silicon surface to prevent from the texturing process. The reflectivity, the surface morphology and the etching rate are used to evaluate this texturization method. The influences of the size of the openings and the separation between grids and wafers on reflectance are studied. Under optimized conditions, uniform pyramids are fabricated. An average reflectance of 10.7% is obtained without any anti-reflectance coatings. Compared to the traditional methods this new texturization process doesn't need any surface-active additive. The material cost of etching process has been reduced from 0.064USD/wafer to 0.025USD/wafer. The proposed technique offers a new way to fabricate textured surfaces for silicon solar cell.