Nondestructive Testing Of Silicon Solar Cells Based On Lock-in Infrared Thermography

The energy crisis and green house effect are becoming more and more serious, the solar cell, as a kind of green energy has been widely used in various fields in our life. The defect detection technology plays an important role in the production process of solar cells. Therefore, the nondestructive testing technology of solar cell has an significant effect on the development of solar cell.In this research, we selected three different kinds of solar cells (monocrystalline silicon, multicrystalline silicon and thin film silicon) as the research objects. We described and classified the defect from the fundamental structure, optical-electrical characteristic and production process of silicon solar cells. Several common solar cell detection methods were introduced and compared from the principle and characteristics. Based on the comparative results, we select an effective nondestructive testing technology-lock-in thermography technology as the main research method.In this thesis, two kinds of lock-in thermography technology were used to the detection and analyses for the defect of silicon solar cell. The first one is dark current lock-in thermography technology (DLIT),0.5 V forward and reverse bias applied on the solar cell, we can obtain some information of leakage current (linear or nonlinear) by comparing the thermal image analyzing. Increasing the value of reverse bias to 30 V, we can obtain some important information of defect by comparison the change of defect area. The second one method is illuminated lock-in thermography technology (ILIT), on the basis of DLIT technology with LED lights and 850 nm infrared light irradiation. Based on the comparative of the thermal image and compared with the results of DLIT, we can obtain the cause of defect. The characteristics of defect can be described by detecting the relationship between the surface temperature of solar cell sample surface and time. We also can determine the defect depth and size by calculate the amplitude and phase. Finally, in order to verify the validity and accuracy of this method, we test the same solar cell samples with Corescan method by comparing the relationship between series and parallel resistance and dark current.