An OLED device includes: a first substrate having a bonding surface; a second substrate having a first surface; a coloring unit including an OLED layer and optionally a color-transformation layer, the OLED layer being formed on a selected one of the first and second substrates, the color-transformation layer being formed on the second substrate; and a pixel circuit with TFT functions disposed on the first substrate and coupled to the OLED layer. The bonding surface of the first substrate and the first surface of the second substrate are in direct bonding.