Patent ID: 7084564

Claim:
An organic light emitting device, comprising: an anode layer formed on a substrate; a first mixing layer formed over the anode layer, wherein a material of the first mixing layer is a mixture of a hole transport material and an electron transport material; a mixing layer formed on the first mixing layer; wherein a material of the mixing layer is a mixture of an organic light emitting material, the hole transport material and the electron transport material; a second mixing layer formed on the mixing layer, wherein a material of the second mixing layer is a mixture of the hole transport material and the electron transport material; and a cathode layer formed over the second mixing layer; wherein, when a volume ratio of the hole transport material to the electron transport materials in the mixing layer is X %, a volume ratio of the hole transport material to the electron transport materials in the first mixing layer decreases gradually from 99% to X % starting from a surface adhered to the anode layer, wherein a volume ratio of the hole transport material to the electron transport material in the second mixing layer increases gradually from X % to 99% starting from a surface adhered to the mixing layer.