The Key Techniques Research Of Back Surface Field In Bifacial N-type Crystalline Silicon Solar Cells

In the 21^st century,the situation of global energy shortage and environmental degradation facing mankind is becoming more and more serious,the development of traditional fossil energy has encountered bottleneck,hence renewable energy is being supported and developed as strategic targets by many countries.Solar photovoltaics has many advantages compared to other renewable energy,such as no pollution,strong compatibility and various installation place.Photovoltaics is expected to exceed hydropower generation and become the second energy industry,with the cost per kilowatt hour decreasing.It is estimated that by 2021,the global new photovoltaic installation will reach 109 GW,and the total photovoltaic capacity will add up to720 GW.Therefore,upgrading the industrialization of solar cell technology has become the key to the application of photovoltaics.Currently p-type solar cells are the main products on the market,but n-type silicon has been recognized gradually,researched and promoted because of the characteristics of high minority carrier lifetime,low degradation and more suitable for high efficiency cell structure.Our country has also set up projects for high efficiency and low-cost n-type silicon solar cells.The main purpose of this research is to solve the key problems of the n-type silicon solar cell's back surface field in the industrial application,study the efficiency loss mechanism of n-type silicon solar cell,and find the industrial solution.To take full advantages of n-type silicon,this paper optimizes the performance of back surface field in the cell production process,enhances the sunlight absorption and management,increased the cell efficiency through bifacial structure and back contact structure design,and realizes the industrial production.The main research achievements are as follows:?1?The simulation results indicate that recombination from back surface non-contact area and power loss caused by bulk resistance contribute to the main energy loss of n-type solar cells.In this study,phosphorous ion implantation technology was applied to fabricate the back surface field,and the effects of implantation process parameters on back surface field were investigated.The best conversion efficiency was achieved by using implantation dose 3.00×10¹⁵ atoms/cm²,annealing temperature 900?and annealing time 20min.Meanwhile,the industrialization process of n-type solar cell is integrated to get the mass production average efficiency more than 21%,through tuning of back side polishing,chemical passivation and bulk resistivity.?2?In this study,selective back surface field was fabricated on normal n-type solar cell by etch-back mask and wet chemical etching method.The relationship between sheet resistance after etching and surface doping concentration,recombination current and cell efficiency was investigated.With sheet resistance increasing,the recombination current decreased,and the cell efficiency achieved the best value when the Rsheet is 60?/?.Considering both the electrical property increasing and printing alignment problem,200?m mask width was chosen to an excellent electrical property.Finally,with the optimization of back contact and passivation,the selective back surface field can increase open-circuit voltage by 8 mV,short-circuit current concentration by 0.65 mA/cm² and the cell efficiency by 0.4%,compared to the normal process.The maximum cell efficiency reached 21.08%tested by the third party.?3?In order to further improve the shielding of solar cell front electrodes,explored and used the conventional solar cell equipment,bifacial IBC solar cell was fabricated by screen printing,and the process flow was optimized.The study found that,with the etching sheet resistance increasing,the Voc and Isc increased before the etching sheet resistance reached 95?/?,while the Voc and Isc decreased when the etching sheet resistance above 105?/?because of the low doping concentration.The IBC solar cell's efficiency reached the best when the etching sheet resistance was 95?/?after boron diffusion.Meanwhile,new screen pattern of the back surface was adopted to make an obviously improvement on Voc,Isc,FF,and Eff.The cell conversion efficiency increased 1.24%and the average cell efficiency reached 20.5%.The best cell efficiency reached 21.08%tested by the third party.