Efficiency and reliability improvement of silicon nanocrystals in silicon oxide light-emitting devices is reported. The emission power efficiency is enhanced up to ~1 % by depositing a ~15-nm silicon nitride buffer onto the active layer. The presence of this additional layer reduces the leakage current through the structure, leading to an effective increase of the power efficiency without significant effects on the operation voltages. Furthermore, the silicon nitride cools down the electrons that reach the top electrode. Both effects lead to a device degradation reduction of up to 50 %.