Electrical And Mechanical Properties Research Of Crystalline Silicon For Solar Cells

With the improvement of people's awareness of environmental protection and the government's strong support for environment-friendly energy,solar energy has been vigorously supported by the state due to its inexhaustible advantages and the characteristic of pollution-free in photoelectric conversion process.In the photovoltaic industry,crystalline silicon solar cells account for more than 80%of the share,and its highest laboratory efficiency has exceeded 27%.The current development direction of commercial crystalline silicon solar cells is low cost and high efficiency.The main way to reduce the cost is to continuously reduce the thickness of the crystalline silicon.The main way to improve the efficiency is to handle well surface passivation of the crystalline silicon,thereby reduce the surface recombination and improve the photoelectric conversion efficiency(PCE).With the advancement of solar cell thinning,more and moer warpage and fragment will appear.Even the presence of subtle impact on the mechanical properties of silicon wafers in production may lead to unqualified chips.The quality of surface passivation of silicon solar cells is directly affects the PCE.In addition,when the crystalline silicon solar cell or the silicon-based microelectronic device is run in the irradiation environment,high-energy irradiation particles will introduce defects in the silicon,which is disadvantage to the device.Therefore,this thesis focuses on the study of the mechanical and electrical performance parameters of crystalline silicon for solar cells in practical production and working environments,and the following conclusions are obtained:The effects of Cu contamination on the mechanical properties of polycrystalline silicon grains,SA grain boundary,?3 grain boundary and R boundary were studied.It was calculated that the hardness of grains,SA grain boundaries and ?3 grain boundaries are not much different,between 11?12GPa,while the hardness of the grain boundary R reached 18 GPa.After the introduction of Cu contamination,the hardness of all grain boundaries and grain decreased,and the hardness of R boundary decreased by 33%.The electrical performance of V2 and VO defects introduced by neutron irradiation in pn junction were quantitatively calculated by DLTS.The activation energy and defect density of V2 and VO are calculated when the irradiation dose is 5×10cm-2,1×1012cm-2,6×1012 cm-2,1×1013cm-2 and 5×1013 cm-2.It was found that the density of V2 and VO defect states had a linear relationship with the radiation dose,and the proportionality coefficients were calculated to be 0.18 and 0.38,respectively.And through the current and voltage test,it was also found that as the density of V2 and VO defect states increases,the ideal factor ? and the reverse current IR increase,that is,the device performance deteriorates.The effects of Al2O3,TiO2 and HfO2 on the surface passivation of single crystal silicon were studied,and the photo-intensified effect of the material was explored.It was found that the optimal annealing temperatures for Al2O3,TiO2 and HfO2 were 450?,500? and 300?,and HfO2 and Al2O3 had the same photo-enhancement effect,while TiO2 had the photo-reducement effect.We speculate that this is because HfO2 has a field passivation and chemical passivation mechanism similar to Al2O3,that is,both of them can capture and pin negative charges after illumination,thereby enhancing the field passivation effect.While the fixed positive charge will be generated under light conditions in TiO2,which may instead weaken the field passivation effect.