Development of High-Efficiency n-Type Front and Back Contact Passivated Emitter and Rear Locally Diffused Solar Cells Using Atmospheric Pressure Chemical Vapor Deposition of Phosphosilicate Glass and Laser Processing

Industrial bifacial n-type front and back contact (nFAB) silicon solar cells, consisting of a boron-doped p⁺ emitter and a phosphorus-doped n⁺ back surface field (BSF), are known to give good bifaciality, high and stabilized efficiency. One possible approach to further enhance the cell efficiency is to convert conventional passivated emitter and rear totally diffused (PERT) into rear locally diffused (PERL) structure. Herein, bifacial nFAB PERT and PERL cells are fabricated by combining atmospheric pressure chemical vapor deposition (APCVD) of phosphosilicate glass (PSG) as doping source and laser processing. For PERL cells, two approaches are studied to locally form phosphorus-doped BSF: 1) laser doping, and 2) laser ablation of a diffusion barrier layer. For ablation approach, an alkaline treatment is introduced immediately after laser process, which leads to the formation of locally textured BSF. Due to this locally textured contact, the resultant fill factor (FF) and series resistance (R_s) loss of the PERL cells are even less than that of the reference PERT cells. As a result, the champion cell of PERL shows a good efficiency of 21.3% with open-circuit voltage (V_oc) of 662 mV, short-circuit current density (J_sc) of 39.6 mA cm⁻², and a high FF of 81.1%.