Solar Energy Materials and Solar Cells, Vol.157, 326-330, 2016
Bifacial, fully screen-printed n-PERT solar cells with BF2 and B implanted emitters
For boron implants made with ion implanters designed for PV applications, a variety of ion species BFx, (x=0.2) is implanted, while BF2 accounts for the lions share. We investigate the impact of the BF2 implantation dose and the annealing conditions on the resulting electrical characteristics of industrial bifacial n-type PERT solar cells. For an annealing temperature of 950 degrees C, we observe a steep increase in the emitter saturation current density for BF2 implant doses above 1.75 x 10(15) cm(-2). We compare co-annealed BF2- and B-implanted solar cells and achieve maximum energy conversion efficiencies of 20.6% with BF2 and 21.0% with B, respectively. Separate annealing processes for the p(+) and n(+) doped regions result in even higher energy conversion efficiencies of 20.8% with BF2 and 21.5% with B emitter implant. An optimized double-layer ARC applied on the separately annealed cells further increases the efficiency up to 20.9% for BF2 and up to 21.8% for B emitter implant All efficiency values are independently confirmed. The solar cells have bifacial factors between 97.3% and 99.4%. The BF2-implanted solar cells with highest efficiency feature an emitter with a sheet resistance of 180 Omega/sq. contacted by a commercially available Ag/Al paste with specific contact resistance of less than 10 mfg cm(2). (C) 2016 Elsevier B.V. All rights reserved.