The improved organic electrophosphorescence devices(PhOLEDs) are fabricated by inserting an ultrathin CBP layer as triple exciton block layer at the interface between hole transport layer(HTL) and emitting layer(EML),and their electrical and emitting properties are investigated.The PhOLEDs have the ITO anode/NPB/CBP(x nm)/CBP:Ir(ppy)3/BCP/Alq3/LiF/Al cathode structure.For the PhOLEDs with 2 nm CBP ultrathin layer,the maximum efficiency is 13.1 cd/A at 8 V.Compared with the device without CBP ultrathin layer...