The Research On The Performances Of MWT/PERC Solar Cells Effected By Rear Laser Ablation

The technologies of Metal Wrap Through(MWT)and Passivated Emitter and Rear Contact(PERC)are applicated for the novel type of high efficiency thin Si solar cells.These cells combine the rear passivation effect with the unique cell structure of MWT,which are able to obtain higher conversion efficiency and reduce the loss of materials.Since the rear passivation layer is insulative,a certain pulse of laser needs to be applied to a local area on the rear surface to achieve a good electronic path.The electrical performances and the spot shapes can be effected by the different laser parameters and patterns.So the conversion efficiency can be improved by adjusting the laser parameters.In addition,the cells’bowing phenomenon of thinner silicon wafer can be effected by the laser ablation area and patterns,so a reasonable design is a way to improve the bowing.Therefore,the research on the laser ablation process is very important,which caused extensive research and discussion in recent years.This dissertation focused on the laser ablation process in the mono-crystalline silicon MWT/PERC solar cells,including the optimal matching of related laser parameters,the design of the optimal laser ablation rate on rear surface,the optimization of line width based on the optimal laser ablation rate,the mechanism of cells bowing,the influence of different laser ablation area on cells bowing and the design of a new laser ablation pattern on the rear surface.Through the above researches,the cells bowing was improved,as well as improving the electrical performances.Based on the principle of laser ablation process,the laser power,laser scanning speed,and laser repetition frequency were discussed in this dissertation,and the optimal matching schemes was proposed.After that,through the theoretical analysis and experiments,this thesis proposed a scheme of optimal laser ablation rate.On the basis of them,the better matching scheme of line width and line density were proposed,which improved the conversion efficiency of the solar cells by nearly 0.10%abs.In addition,the related pattern parameters of laser ablation on rear surface was discussed and the matching of the relevant parameters was achieved based on the optimal laser ablation rate.Aiming at the cells bowing,combined with Ⅰ-Ⅴ test data,Abaqus finite element analysis(FEA)and experiments,the optimal laser ablation rate was determined in this dissertation and the electrical performances and the bowing of the solar cell were ideal.Keeping the laser ablation area as a constant,this thesis proposed a novel Al-Si contact pattern.The stress was more dispersed by this pattern after firing and cooling in order to improve the bowing.Through experiments,compared with the conventional pattern,the bowing of the new dot pattern was reduced by 0.397 mm,i.e.reduces by 18.704%.The bowing was improved by this type of dot pattern,which provided ideas and methods for subsequent improvement of bowing effect.All the work done in this dissertation were verified by theory,simulation and experiments,which can be used in production in the future.It was not only authentic and reliable,but also innovative,which provided ideas and basis for further to improve the conversion efficiency and reduce the bowing of the thin Si solar cells.