High efficiency screen-printed n-type silicon solar cell using co-diffusion of APCVD boron emitter and POCl3 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. In a single high temperature step, a BSG/SiOx stack deposited by APCVD and a POCl3 back surface field diffuse into the wafer to form the boron doped emitter and phosphorus doped back surface field. The SiOx 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. This resulted in an initial sheet resistance of 76 Omega/square with good uniformity and a final p(+) emitter sheet resistance of 97 Omega/square after boron rich layer removal. 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 POCl3 gettering effect. 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 enhancement. (c) 2017 Elsevier B.V. All rights reserved.