Electrical and optical analysis of dielectric layers for advanced passivation of BBr3 diffused p+ emitters in n-type c-Si solar cells

Abstract

Due to a different surface concentration and type of minority charge carriers compared to n+ emitters (on p-type substrates), novel surface passivation methods are required when using p+ emitters on n-type silicon for which a number of efficiency records have been achieved in recent years [1,2,3]. In this study emitter saturation current densities j0e of two BBr3 diffused emitters passivated by a variety of dielectric stacks are compared using following processes: SiOx by dry thermal oxidation, direct and remote plasma enhanced chemical vapor deposited SiNx, atomic layer deposited Al2O3, SiOx remaining from the RCA standard cleaning process [4] yielding the lowest j0e of 17.5 fA/cm² for a sample passivated by an Al2O3/SiNx stack. Furthermore, the j0BSF values of POCl3 diffused n+ surfaces passivated by several passivation layers are determined as they are applied at the solar cell rear side. The resulting combined j0e and j0BSF values j0combined are compared with IV characteristics of solar cells passivated by the corresponding passivation of emitter and BSF on front- and rear side. As passivation layers are additionally employed as antireflection coatings also the spectral reflectance of the investigated passivation stacks with optimized thickness was determined.