Organic light-emitting diodes(OLEDs) composed of a novel fluorene derivative of 2,3-bis(9,9-dihexyl-9H-fluoren2-yl)-6,7-difluoroquinoxaline(F2Py) were fabricated,and exciplex emission was observed in the device.To depress the exciplex in an OLED for pure colour light emission,4,4'-N,N'-dicarbazole-biphenyl(CBP) was inserted as a separator at the donor/acceptor interface.It was found that the device without the CBP layer emitted a green light peaking at 542 nm from the exciplex and a shoulder peak about 430 nm from F2Py.In contrast,the OLED with CBP layer emitted only a blue light peak at about 432 nm from F2Py.Device efficiencies were calculated by a simulative mode in an injection controlled type mechanism,and the results showed that exciplexes yield much lower quantum efficiency than excitons.The device with CBP has a higher power efficiency as no exciplex was present.
