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

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 ohm 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 m ohm 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 BBr3 diffusion and subsequent TOPCon deposition and annealing reaching 23.1%.

Automated summary

In this article, a simplified processing method for n-type silicon-based TOPCon solar cells is proposed by reducing the number of high temperature processes. Rapid vapor-phase direct doping (RVD) technology is used for simultaneous emitter formation and annealing of the TOPCon layers. The optimized solar cells exhibit high efficiency and low contact resistance.