Study On The Preparation And Performance Of Front Emitter And N-Type Bifacial Solar Cell

In recent years,with the development of photovoltaic industry,N-type crystalline silicon solar cells have attracted more and more attention.The main reason is that N-type crystal silicon solar cells have advantages of high lifetime,no light induced degradation and good weak light effect for solar cell modules.For the N type solar cell,boron diffusion was the critical technology to form PN junction which directly influences the cell performances.Boron emitter as the key factors affecting the performance of N-type solar cell performance.At present,there was no clearly technology to form high quality boron emitter.The technology of liquid source BBr₃ diffusion and spin coating boron source diffusion are studied systematically.Finally,the optimized technology was selected through experiment to fabricate N-type solar cell.Firstly,in this thesis,the PC1D software was used to simulate the effects of different front boron emitter?different surface concentration and junction depth?on the performance of solar cells.The optimized boron emitter can be get by simulation results,which can provide an optimized direction for this experiment.Secondly,the liquid source BBr₃ diffusion technology was used to form a front boron emitter of N-type solar cell.Different boron doped emitter curve was get by changing the diffusion process conditions.The influences of drive-in temperature,drive-in time and the flow of liquid boron sources on front emitter were studied.Through experiment and simulation,the best diffused conditions was found for liquid source BBr₃ diffusion technology.At the same time,the German WEP ECV-CVP21was used to test the surface concentration and junction of the silicon wafer after diffusion,which makes a further study on the effects of boron emitter on the performance of solar cell.The SiO₂ nanosphere was used to assist boron spin-on dopant diffusion technology to form a front boron emitter of n type solar cell.Scanning electronic microscope,four probe method,minority carrier lifetime measurement and ECV measurement were used to test the properties of Si wafer after diffusion.According the test,we can deeply study the effects of SiO₂ nanosphere,diffusion temperature and diffusion time on the properties of boron emitter.In order to make a further improvement on boron emitter,the nanosphere SiO₂ and in-situ oxidation were combined to remove boron rich layer,which is extremely harmful to boron emitter.In the end,the high quality boron emitter was prepared by optimizing diffusion conditions.Finally through the comparison of the above two technology of preparing boron emitter,the SiO₂nanosphere assisted boron spin-on dopant diffusion technology was selected as the optimal boron emitter preparation technology.The boron surface concentration decreased from 7×10¹⁹cm³ to2.8×10¹⁹cm³ and the junction depth increased from 0.3?m to 0.6?m by changing the diffusion conditions which can improve the properties of boron emitter.On the other hand,the SiO₂ nanosphere and in situ oxidation was combined to remove boron rich layer enhanced the wafer minority carrier lifetime and the passivation effect of boron emitter.Finally,the boron emitter of N-PERT solar cell was prepared by this process,the efficiency of the solar cell has reached 20.26%.The performance of prepared solar cell were tested,including IV test,QE test,EL test and the study of light induced degradation phenomenon.Compared to the ordinary process,the efficiency of the solar cell was improved 0.23%absolutely by using the optimized boron emitter technology.