This application relates to an OLED device, a manufacturing method thereof, and a display device. The OLED device includes a light emitting unit between an anode and a cathode. The light-emitting unit includes: a first carrier function layer for migration of first carriers, the first carrier function layer including a first material layer; a second carrier function layer for migration of second carriers having a polarity different from that of the first carriers, the second carrier function layer including a second material layer; a light emitting layer between the first material layer and the second material layer, the light emitting layer including a luminescent material; a first buffer layer between the light emitting layer and the first material layer. The first buffer layer is a mixed layer containing the luminescent material and the first material.