High-efficiency and low-voltage organic light-emitting device(OLED) with a composite hole transport layer(c-HTL) of m-MTDATA doped into NPB was demonstrated.With Alq3 as the emitting and electron transport layer,the maximum luminous efficiency of OLED using c-HTL reached 5.3 cd/A which was much higher than that(3.4 cd/A) of the device with NPB as HTL.The c-HTL can improve the device efficiency by a factor of ~1.5,which is because the dopant of m-MTDATA(5 wt%) reduced the hole mobility of c-HTL and thereby p...