Dielectric layers are of major importance in crystalline silicon solar cells processing, especially as antireflection coatings and for surface passivation purposes. In this paper we investigate the fixed charge densities (Q(fix)) and the effective lifetimes (tau(eff)) of phosphorus (P) and boron (B) doped silicon nitride layers deposited by plasma-enhanced chemical vapour deposition. P-doped layers exhibit a higher tau(eff) than standard undoped layers. In contrast, B-doped layers exhibit lower tau(eff). A strong Qfix decrease is to be seen when increasing the P content within the film. Based on numerical simulations we also demonstrate that the passivation obtained with P- and B-doped layers are limited by the interface states rather than by the fixed charges. (C) 2012 Elsevier B.V. All rights reserved.