Liquid-phase crystallization (LPC) of thin silicon layers on glass substrates is a technique to fabricate solar cells with low energy and material consumption and open-circuit voltages comparable to multicrystalline silicon wafer cells. We studied the impact of different passivation layers deposited with plasmaenhanced chemical vapor deposition (PECVD) on the cell quality. Silicon nitride (SiNx) and ultrathin silicon oxide (SiOx) layers with varying thicknesses were used. In addition, we plasma-treated the SiNx surface to form a thin silicon oxynitride (SiOxNy) passivation layer. Plasma oxidation is an attractive alternative to PECVD, since thicknesses of ultrathin layers can be controlled easier as compared with PECVD.We found that the cell performance is influenced by the passivation layer. Particularly, cells on the 9 nm PECVD SiOx passivation layer are worse than cells on the 11 nm SiOxNy layer. We modeled cell parameters employing ASPIN3 to estimate effective diffusion lengths. Using transmission electron microscopy as well as electron energy loss spectroscopy, we studied the effect of the plasma treatment on the morphology and elemental distribution at the interface between passivation layer and LPC-Si absorber. Our best interdigitated back contacted solar cell with an efficiency >14% is based on the SiOxNy layer.