An organic light-emitting device including a barrier layer that includes a silicon oxide layer and a silicon-rich silicon nitride layer. The organic light-emitting device includes a flexible substrate that includes a barrier layer and plastic films disposed under and over the barrier layer. The barrier layer includes a silicon-rich silicon nitride layer and a silicon oxide layer. The order in which the silicon-rich silicon nitride layer and the silicon oxide layer are stacked is not limited and the silicon oxide layer may be first formed and then the silicon-rich silicon nitride layer may be stacked on the silicon oxide layer. The silicon-rich silicon nitride layer has a refractive index of 1.81 to 1.85.