Simultaneous Boron Emitter Diffusion and Annealing of Tunnel Oxide Passivated Contacts Via Rapid Vapor-Phase Direct Doping

Abstract

n-type silicon-based tunnel-oxide passivating contact (TOPCon) solar cells are a cell concept reaching highest power conversion efficiencies. In this article, we demonstrate a substantial simplification of processing such TOPCon solar cells by reducing the number of high temperature processes. To this end, rapid vapor-phase direct doping (RVD) processes are applied for emitter formation and simultaneous annealing of the TOPCon layers within one process. RVD emitters with sheet resistances of 200 Ω sq -1 reach low emitter saturation current densities of 26 fA cm -2 on textured surfaces. Thermal interface oxides of the TOPCon layers were adapted to withstand the increased thermal budged of the RVD process. Optimized layers exhibit a saturation current density of less than 1 fA cm -2 and a contact resistance of 5 mΩ cm 2 . The best solar cell with the simultaneous emitter diffusion and TOPCon annealing during the RVD process reaches a confirmed efficiency of 23.3%, similar to a reference with sequential BBr 3 diffusion and subsequent TOPCon deposition and annealing reaching 23.1%.