The organic light-emitting diodes (OLEDs) with a structure of ITO/CuPc(25 nm)/NPB(40 nm)/Alq3(xnm)/C60(ynm)/LiF(1 nm)/Al(100 nm) are prepared.The results show that the current density-voltage curve shifts to right with the increase of the thickness of Alq3,which reduces the power efficiency.However,if the thickness of Alq3 is too thin,there would be serious exciton quenching caused by the cathode of LiF/Al.The device with 45 nm Alq3 has the best power efficiency for the devices without C60 inserting layers....