Design Of A Light-Beam-Induced-Current Detection System For Solar Cell Damage Detection

Solar cell defect detection is an important part of the solar cell production process.Among the existing technologies,light-beam-induced-current(LBIC)mapping technique has the advantage of high resolution and has been used for mapping the spatial distribution of defects in solar cell.It’s great significance to solar cell defect evaluation.The biggest shortcoming of LBIC mapping technique is the long measurement time,which severely limits the application of LBIC technology in industry.For this reason,a set of high-speed and high-resolution LBIC imaging system was designed in this paper,and the selection of measurement light source is optimized.At the same time,this system was applied to investigate the damage of continuous laser to solar cell.To reduce the measurement time,this paper has designed a high-speed LBIC system.The system utilizing galvanometer as scanning component,source meter as measuring component and f-theta lens to achieve high-speed and high-precision scanning.Aiming at the noise introduced from power line caused by too fast measurement speed of source meter,the soft threshold wavelet transform is used to reduce noise and realize high-precision current measurement.The test result shows that the beam spot diameter is 34μm,and the measurement speed is 1902 points/s.In order to select the detection light wavelength and power,theoretical and experimental researches have been carried out.A two-dimensional finite element model is established to investigate the influence of light source wavelength and power density on the measurement results.Simultaneously,experimental research is carried out.Both numerical and experimental results show that the defect detection capability is not affected by power density,but related to wavelength.When the penetration depth of the light source is consistent with the defect depth,the defect detection capability is the strongest.Based on the designed high-speed LBIC system,the laser damage mechanism of solar cells was experimentally studied.A silicon solar cell was irradiated by 1080 nm continuouswave(CW)laser to induce damage to the solar cell,then using LBIC system to measure the spatial variation of photocurrent of the solar cell.The results showed that with the increase of laser power density or irradiation time,solar cell damage first occurred inside,and then the surface began to be damaged;before the surface melted,the lose efficacy zone had already occurred inside the cell.When the laser irradiates fingers with high power density,the fingers will melt,and the photocurrent on the side of the irradiated position away from electrode will decrease.In severe cases,the solar cell will have cracks perpendicular to fingers,lead to lose efficacy.The research results in this paper can provide references for the detection and location of solar cell defects,defects and short circuits areas,and the research on damage mechanism of solar cells irradiated by CW laser.