Mechanical Properties Of Crystalline Silicon Materials And Related Technology Of Solar Cells

Photovoltaic (PV) industry is globally booming due to the energy resource crisis, and the silicon solar cells used for optical-to-electrical conversion are the main products on the PV market. However, the bottle-neck restricting the wide application of silicon solar cell is still its high cost, among which the silicon material is a main cost item. Therefore, the silicon solar cell tends to become thinner and thinner in order to save the consumable material. But, thinning the wafer will cause the degradation of mechanical strength and the increase of breakage and warpage. These are very detrimental for the performance and yield of silicon solar cell. Thus, it is significantly necessary to investigate the mechanical properties of thin wafer and find an optimum way to reduce the mechanical strength degradation of thin wafer.This dissertation is focused on the mechanical properties of crystalline silicon solar cell, including the following aspects,(1) The effect of germanium doping on the mechanical properties of cast multicrystalline silicon has been investigated. It is found that the germanium can significantly enhance the mechanical strength of silicon material by 16-21%, compared to the conventional ones. This enhance effect can also be found after the phosphorus diffusion technology. It implies that germanium-doped silicon with strong mechanical strength is a promising substrate for thin solar cell.(2) The dislocation slip near grain boundary (GB) and the effect of GBs on the mechanical property of silicon have been investigated. It is found that the GB can cause a barrier for the slipping of dislocation, and therefore the dislocation cannot slip through the GB. Meanwhile, the GB can reduce on the characteristic parameters of silicon mechanical properties to some extent, such as young's modulus and hardness. The young's modulus and hardness at the GBs are averagely smaller than those in the grains.(3) The evolution of mechanical property during cell fabrication is studied. It is found that the texturing and Si₃N₄ film deposition can improve the wafer fracture strength, while the phosphorus diffusion, screen printing and metal contacts firing will decrease the fracture strength. The mechanical strength of solar cell can be effectively improved by modifying the busbar pattern on the rear. In summary, the achievements in this dissertation have supplies the necessary science understanding and technology support for the practical application of germanium-doped silicon solar cell on the mechanical properties, the interaction of dislocations with the GBs and the evolution of mechanical strength in the process of cell fabrication.