Significant surface related degradation (SRD) is observed in samples passivated with either SiNx:H or AlOx:H/SiNx:H during treatment at 150 degrees C and 1 sun equivalent illumination intensity. Degradation of SiNx:H passivation is caused by a decrease of chemical passivation quality whereas degradation of AlOx:H/SiNx:H is caused by a decrease of fixed charge density. SRD is, however, strongly suppressed on highly doped silicon surfaces resulting from a diffusion step. Device simulations indicate that this cannot only be explained by reduced sensitivity to changes at the silicon surface due to the diffused region, and implications for defect formation are discussed.