The current and electroluminescence(EL) of magnetic field dependent organic light-emitting diode(OLED) with the structure of ITO/NPB(40 nm)/BAlq(60 nm)/BCP(5 nm)/LiF(0.8 nm)/Al were measured at room temperature.It has been found that the efficiency increases by up to 34% as the magnetic field increases to 10 mT,which suggests that the increase of device efficiency is due to the conversion of triplets into singlets through triplet-triplet annihilation.The current-voltage characteristic curves show that the r...