Research On Doping And Metallization For Crystalline Silicon Solar Cells

Crystalline silicon solar cells occupy a dominant position in the global photovoltaic market.With a constant demand for low cost,high-efficiency solar cell structures have gradually entered the industrialization stage such as Passivated emitter and rear cell(PERC),Heterojunction with intrinsic Thin-layer(HJT),Tunnel Oxide Passivated Contact(TOPCon)solar cell,etc..Although high-efficiency solar cells effectively have reduced the recombination of photo-generated carriers on the rear surface of the solar cell,the low sheet resistance of the emitter also limits the further improvement of efficiency,and the sheet resistance uniformity of high-efficiency solar cells has been one of the hot spots of industrialized technology.In addition,on the technology pathway of n-type high-efficiency solar cells,low-temperature rear metallization has gradually become the focus of attention in the photovoltaic industry as another important means of reducing costs.Three aspects of the establishment and simulation of the diffusion theory model,the diffusion process method,and the low-temperature rear metallization process were addressed in this paper:(1)A theoretical model of the non-uniform emitter process was established,aiming at investigating the cause of non-uniform sheet resistance in the process,resulting in the realization of accurate prediction on diffusion process trend.(2)The manufacturing process of a highly uniform emitter was realized,which solved the industry problem that tube diffusion is difficult to achieve high and uniform sheet resistance,and verified the guiding role of theoretical simulation in experiments.(3)A low-temperature preparation process of metallization of solar cells was first realized in China,and excellent performance was achieved on n-Pasha solar cells.The following results have been obtained:(1)The simulation of the phosphorus/boron diffusion process showed that the higher the drive-in temperature,the greater thickness of PSG/BSG,and the deeper concentration of phosphorus/boron in PSG/ BSG,the deeper junction and lower the sheet resistance were achieved.The device simulation showed that the cell performance under the condition of low doping concentration(high sheet resistance,shallow junction)was better than that with high doping concentration(low sheet resistance,deep junction).Uniform junction depth can obtain a better cell performance.Simulation of rear metallization contact characteristics showed that the specific contact resistivity between metal and semiconductors increased with the increase of work function.Device simulation showed that the lower the work function,the higher the open-circuit voltage and the higher the cell efficiency.(2)The manufacture of phosphorous emitters without metal contamination by ceramic roller inline diffusion(CRID)was investigated.With the target sheet resistance of 85 Ω/sq,the deviation of sheet resistance for CRID and tube diffusion(TD)were 3.2Ω/sq and 5.65Ω/sq,respectively.CRID can obtain a standard deviation of cell efficiency of 0.02%,which was 81.8%lower than the TD process.Combined with the Suns-Voc test,it was shown that the uniform emitter of CRID cell had the potential for higher efficiency improvement,which catered to the multi-busbar design of higher efficiency in the future.Comparing the performance of TD cells with different sheet resistance deviations at the same sheet resistance target,the results showed that the smaller of sheet resistance deviation,the higher shortwave response,and the higher Voc and efficiency.(3)The contact characteristics and performance of n-Pasha solar cells with Ti/Ag,Hf/Ag,Mg/Ag,and Ag as the rear metallization layer were investigated.The results showed that Mg rear contact to n-type crystalline silicon solar cells had good contact characteristics with the lowest serial resistance of 0.24 Ω.Compared with the Ag contact layer,the Voc of cell with Mg contact layer was increased by 47 m V,up to 8.95%(relative)and the FF of Mg contact cell was increased by 1.34%(absolute),resulting in a higher increase of efficiency by 1.5%(absolute)and 10.5%(relative),respectively.Thus,this new technique can be exactly catered to the demands of rear metallization for novel n-type silicon-based solar cells.The non-uniform emitter process model in this paper accurately predicted the profile impurity distribution of the actual process,which provided theoretical support for parameter optimization in the actual process innovation.The manufacturing process of high uniform emitter not only verified the guiding role of theoretical simulation in experiments,but also provided a technical pathway for the realization of the multi-busbar process.The lowtemperature manufacturing process of metallization not only verified the guidance of theoretical simulation but also provided a scheme for low-temperature metallization with low cost.