The Simulation And Technology Of Silicon Surface Etch For Solar Cell

Along with the development of human society, energy problem is becoming more and more seriously, energy has become a "bottleneck" of human society continued development. Seek a new energy of low consumption, low pollution and low emission has become an urgent problem to be solved which including nuclear energy, geothermal energy, wind energy, biomass energy, solar energy and so on. And solar energy is the most important new energy of the new century because of the unique advantage:the inexhaustible, clean and don’t produce any pollution.The solar cell production process including:etch, diffusion, removal phosphorus silicon glass, PECVD, print and firing. Among them, the etch is used to form texture on wafer surface, the texture can effectively reduce the cell surface’s reflectivity and increase the cell’s short circuit current; it is one of the important factors that affect the solar cells photoelectric conversion efficiency. In generally, multicrystalline silicon wafer use the acid solution to etch the surface because of the isotropic principle.In this thesis, put forward a kind of ellipsoid model to simulate the texture morphology of multicrystalline silicon surface firstly, according to observe the morphology of surface that prepare by industrialization production. Keep the long axis length, change the short axis and the depth of the model, eventually, get five models with different sizes. And then use the software FDTD Solutions7.5to simulate and get the reflection spectrum of surface. Compare the difference between simulation result and calculated result, and explain the cause of the difference.Then, do the etch experiment in RENA cleaning machine by using two different kinds of acid solutions:high HF concentration solution (HNO3/HF/DI water=50L/150L/280L) and high HNO3concentration solution (HNO3/HF/DI water=250L/60L/170L), through the change of the belt speed of the RENA machine to change the much time, and get a series of different shape of texture, use laser scanning microscope observe the morphology of the surface, and use the reflection spectrometer to measure the reflection spectrum of the surface. The experimental results show that:the texture prepared in high HF concentration solution is covered with micro cracks, and in high HNO3solution is ellipsoid pits. This is because in the high HF concentration system, HNO3concentration is low, the reaction can only happen in the areas of the lower activation energy, such as crystal defect place; and in high HNO3concentration system, reaction begin in low activation energy area, and then spread to sides, and the etch rate at the edge of the pit is greater than the center, so the cracks grow wider. If etch time is too long, the edge regions etch too much, and the whole pit will become very wide and shallow, reflectivity increase, so the solution play a role of polish the silicon wafer. Finally, compare the simulation results with the experimental results, and we can get high HNO3concentration system is more suitable to the requirements of industrial production. In addition, in the high HNO3concentration system the surface morphology change with the etch time sensitively, so the control of the reaction time is particularly important.