Texturisation Etchant And Structure Of Monocrystalline Silicon Solar Cells

It is an important way to solve the energy problems and environmental issues by using photovoltaic power. Low-cost and high-efficiency are always the two crucial research goals of solar cells. Many measures have been taken to reduce the reflectance of incident light on the surface of solar cells to improve the conversion efficiency.This thesis improved surface morphology of monocrystalline silicon solar cells from both the chemical and physical aspects, using organic alkali etching solution (4-methyl ammonium hydroxide, TMAH) and one-sided texturisation method.The research on TMAH solution includes studying the effect of TMAH and isopropyl alcohol (IPA) concentration, reaction temperature and reaction time on the system. With the increase of TMAH concentration form 0% to 2%, the reflectivity decrease. 2% TMAH (with 10% IPA) can make surface reflectivity decreased to 13.38%. With the solution containing 2% TMAH, 8% IPA can minimize the surface reflectivity to 13.43% by changing IPA concentration form 0% to 18%. Silicon surface reflectance declines with the solution temperature. At 80°C and 90°C, the reflectivity is 13.47% and 13.40%. 80°C is appropriate given the experimental and control costs. A minimum reflectivity of 13.39% can be obtained after 30min reaction. The optimum conditions of TMAH solution is: 2% TMAH, 8% IPA at 80°C for 30min. Comparing with traditional NaOH texturisation, TMAH texturisation has advantages both on antireflection and on ionic contamination. TMAH pyramids have good uniformity and high coverage. The characteristic parameters of TMAH texturisation solar cells are superior to that of NaOH texturisation solar cells with Pm 2.37 W andη16.03%.In one-sided texturisation method, SiNx film is used to prevent back surface reacting with etching solution. 60nm SiNx film can prevent the NaOH solution and form a flat back surface with no pyramids. 30% NaOH solution can basically remove pyramids in 60s and the reflectivity decrease to 31.64%. After 120s, the silicon surface becomes more flat with the reflectivity of 35.63%. Three kinds of back surface morphology can be prepared, in which the performance parameters of flat back surface made by one-sided texturisation method are the best; flat back surface made by sawing pyramids has higher FF, Pm, andηthan normal texturisation back surface. The Rs has greater impact on the FF than Rsh. Flat back surface has better back surface field (BSF) for good uniformity. The BSF thickness of Group 2 is about 13μm, which is agreed with and the theoretical values deduced from the Al-Si phase diagram. In the wavelength range of 440nm-1000nm, Group 2 has the best external quantum efficiency (EQE). Group 3 has better long-wavelength EQE than that of Group 1.