Effective hole-injection layer for non-doped inverted top-emitting organic light-emitting devices

Non-doped inverted top-emitting organic light-emitting diode with high efficiency is demonstrated through employing an effective hole-injection layer composed of MoO_x. One reason for high efficiency lies on the energy-level matching between MoO_x and hole-transport, and another is due to the Ohmic contact formed between MoO_x and Ag. Both of them lead to an improvement of the hole-injection capability from Ag top anode. Moreover, the symmetrical current of “hole-only” device with MoO_x shows better hole-injection capability, which is independent of the deposition sequence. The optimized device with MoO_x hole-injection layer exhibits maximum current efficiency of 3.7 cd/A at a raised luminance level of 14,900 cd/m² and a maximum luminance of 47,000 cd/m² under 18 V.