Ion-implanted PERC solar cells with Al2O3/SiN x rear passivation

Abstract

Ion implantation is an attractive candidate for PERC solar cells due to the single-sided emitter phosphorus doping. The oxide, which is formed during the implant anneal, can be used as rear passivation of PERC cells. However, the SiO2/SiNx rear passivation is very sensitive to the rear surface roughness and surface preparation. Hence, in this paper we evaluate Al2O3/SiNx rear passivation layers in combination with an oxide passivated ion-implanted emitter. We obtain emitter saturation current densities of 93 fA/cm2, which is significantly lower compared to a typical POCl3 diffused emitter with 140 fA/cm2. Ion-implanted PERC cells with Al2O 3/SiNx rear passivation show conversion efficiencies up to 20.0% which is comparable to POCl3-diffused PERC cells. The emitter dopant profile can be adjusted by the thermal budget of the anneal in order to optimize the process window between Jsc and FF losses. The IQE and reflectance of implanted and POCl3-diffused PERC cells in the long wavelength regime are almost identical which demonstrates the successful implementation of the Al2O3/SiNx rear passivation to PERC cells with ion-implanted emitters. Future work will focus on simplifying the process flow in order to obtain a lean industrially manufacturable PERC process, leveraging the single side doping via ion implantation.