To provide a device with high efficiency and high reliability by selecting an energy barrier against hole injection from a hole transport layer to an electron transport layer higher than a barrier against reverse electron injection.
A conducting layer 12 is a p-type contact and a conducting layer 15 is an n type-contact. An negative terminal of a power source 17 is connected to the conducting layer 15, and a positive terminal is connected to the conducting layer 12. When voltage is applied to the conducting layer 12, 15 from the power source 17, electrons injected from the conducting layer 5 is carried to a hole transport layer 13 through an electron transport layer 14, holes injected from the conducting layer 12 are injected to the hole transport layer 13, the electrons and the holes are recombined to radiate photons. Supposing that the work functions of the conducting layers 12, 15 are EM1, EM2, the conducting band level and the valence band level of the hole transport layer 13 are EC1, EV1, those of the electron transport layer 14 are EC2, EV2, the materials for the hole transport layer 13 and the electron transport layer 14 are selected so that inequality, (EC1-EC2)<(EV1-EV2) is satisfied.
LEE HSING-CHUNG
HARVEY III THOMAS B
SO FRANKY
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