n-Type Silicon Solar Cells with Implanted Emitter

Abstract

Ion implantation, which is the state of the art doping technology in microelectronics, is being reintroduced for silicon solar cell processing. High volume manufacturing of solar cells with implanted phosphorus emitters has just begun. However, boron implantation for emitter formation in n-type solar cells seems to be more complicated. Some publications have presented high emitter saturation current densities and low effective lifetimes after implantation and annealing. In this work we present an evaluation of boron implanted emitters for front junction solar cells with a phosphorus BSF. By adapting the annealing conditions we were able to achieve low emitter saturation current densities for the boron implanted emitters. Simulations of the rear side design show that a well passivated full area BSF allows a high degree of flexibility in the choice of base resistivity, whereas a local BSF can lead to slightly higher efficiencies only for low resistivity material. Solar cells with an implanted emitter and locally diffused BSFs were built with an efficiency of 21.7 %, which is comparable to boron diffused reference cells.