| With the development of solar energy,as clean energy,the demand for solar cells with high photoelectric conversion efficiency are now gradually increasing.However,the solar cell production process is complicated.With a multi-layer structure,the causes of defects in different structures of the solar cell are also different.Dark Lock-in Thermography(DLIT)has successfully separated the surface and underlying defects of microelectronic devices.The research for DLIT method used to distinguish defects with different depth of solar cells has a great significance for specifying the physical mechanism of inducing of the defects and improving the fabrication level.Firstly,the heat dissipation mechanism of silicon solar cells was analyzed.The internal defects of solar cells were equivalent to periodic oscillating heat source.On the basis of heat conduction equation and various boundary conditions and combinations,the mathematical model of the defect thermal wave source was established.The thermal transfer function of the defect heat wave source and the point and line spread functions were calculated.The effection of the internal defects to surface temperature signal of the solar cell was clarified.The model was used to study the thermal wave diffusion behavior of solar cell defects,and the phenomena are expounded and summarized.Based on the above research,the defects depth resolution deconvolution strategy was proposed.The feasibility of the methods were verified by simulation analysis.Secondly,based on the theory of dark lock-in thermography and deconvolution strategy,the defect depth resolution of DLIT imaging system for silicon solar cell was established,and DLIT imaging software and defect depth resolution software were developed.The coordination control between software system and hardware system was realized.Finally,monocrystalline silicon solar cell scribing samples and proton irradiation samples with different scales(shape,size,depth)defects were prepared.The influences of relevant experimental parameters on the signal-to-noise ratio of DLIT imaging were analyzed to select the optimal parameters for subsequent experiments and ensure the accuracy of the experiments.The DLIT depth resolution imaging experiments were conducted to the above samples silicon solar cell,achieving accurate separation of defects at different depths and obtain defects depth information with a resolution of 1 μm. |
