Surface recombination of minority charge carriers is a significant loss mechanism in crystalline-Si (c-Si) solar cells. For n+ (phosphorous) doped regions a sufficient surface passivation is achieved by using a silicon nitride (SiNX) film deposited by Plasma Enhanced Chemical Vapour Deposition (PECVD). However, on p+ boron doped regions, SiNX does not passivate the surface. Instead, a stack of layers comprising of a thin silicon dioxide (SiO2), or aluminium oxide (Al2O3), and a SiNX film is commonly used to passivate boron doped regions.In this study we investigated the passivation quality of boron doped emitters by varying the composition of SiO2/SiNX stack layers. For this purpose, n-PERT (passivated emitter, rear totally-diffused) solar cells with boron doped front side emitter and phosphorous doped back-surface-field (BSF), as well as symmetrical boron doped structures, were fabricated on 6-inch n-type wafers.The results show that the optimum passivation is achieved by a stack layer of a thermal SiO2, with a thickness of at least 10 nm, and a SiNX layer with a low refractive index. The chemical composition of SiNX capping layer plays an important role for surface passivation. A more Si-rich SiNX layer show significant degradation in surface passivation of the stack, due to the increase in the density of interface states (Dit) and fixed positive charges (Qtot) at the interface.