A novel organic light-emitting diode by utilizing double hole injection layer

Highly efficient organic light-emitting diode is fabricated with a novel double hole injection layer consisting of MeO-TPD/CuPc. We observe that the insertion of such a double hole injection layer leads to a striking enhancement in the electrical property:higher luminance, power efficiency and lower driving voltage. It has the configuration of ITO/MeO-TPD (15 nm)/CuPc(15 nm)/NPB(15 nm)/Alq3 (50 nm)/LiF(1 nm)/Al(120 nm). Its turn-on voltage is 3.2 V, which is 2, 0.3 and 0.1 V lower than those of the device without hole injection layer (device A) and the devices using MeO-TPD (device B), CuPc (device C) as hole injection layer, respctively. The highest luminance of the novel device reaches 23893 cd/m2 at a drving voltage of 10 V. The maximum power efficiency of the novel decive is 1.91 lm/W, which is 43% (1.34 lm/W), 22% (1.57 lm/W) and 7% (1.79 lm/W) higher than those of devices A, B and C, respectively. The improvement is ascribed to its high hole injection and transport ability. The results are verified by using the J-V curves of "hole-only" devices.