We also developed novel processes for the formation of p +/p ++ selective B emitter by a) single B diffusion with selective etch back and b) two-steps diffusion with implanted B in field region and APCVD B diffusion under the metal grid. This paste reduced the full area metallized Joe,metal from >1100 fA/cm 2 to ~700 fA/cm 2. In addition, we demonstrated metallized recombination current density of ~31 fA/cm 2 for this advanced homogeneous B emitter with industrial screen-printed, fire-through contacts with 40 μm wide grid lines, floating busbars and implementation of an advanced Ag-Al paste which resulted in local or reduced area metal-Si contact under the grid lines with virtually no emitter surface etching. Next, consistent with our roadmap, we developed advanced homogeneous more » implanted B emitter (150-180 Ω/⌫) passivated with ALD Al 2O 3 layer capped with PECVD SiN x/SiO x double-layer antireflection coating This gave a very low recombination current density of 10-15 fA/cm 2 prior to metallization. During this research project, first we developed a technology roadmap to drive the 21% n-PERT cell efficiency from 21% to 23% by transforming the cell design to n-TOPCon and establishing the requirements for each layer, including B emitter, rear n-TOPCon, n-base Si and screen-printed contacts. The overall objective of this program is to achieve ~23% bifacial n-type cell efficiencies by developing and implementing optimized homogeneous or selective boron (B) emitter on front and tunnel oxide passivated contact (TOPCon) on rear side, in combination with advanced fine-line screen-printing metallization with floating busbars. Finally, a peak cell efficiency of 20.3% was achieved and each recombination component in terms of saturation current density was calculated and analyzed to understand the cell for further efficiency = , Additionally, bulk lifetime was investigated before and after the high temperature step that resulted in an increase from 1.2 ms to 1.5 ms due to a POCl 3 gettering effect. This resulted in an initial sheet resistance of 76 Ω with good uniformity and a final p + emitter sheet resistance of 97 Ω after boron rich layer removal. The SiO x layer on top of BSG acts as a masking layer to prevent cross-doping of phosphorus as well as a blocking layer for boron out-diffusion. In a single high temperature step, a BSG/SiO x stack deposited by APCVD and a POCl 3 back surface field diffuse into the wafer to form the boron doped emitter and phosphorus doped back surface field. We present the fabrication and analysis of Passivated Emitter and Rear Totally Diffused (PERT) solar cells on n-type silicon using a co-diffusion process.
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