Enhanced efficiency and brightness in organic light- emitting devices with MoO3 as hole-injection layer

The organic light-emitting devices (OLEDs) using 4,4’,4”-tris{N-(3-methylphenyl)-N-phenylamin}triphenylamine (m-MTDATA) and MoO₃ or 1,3,5-triazo-2,4,6-triphosphorine-2,2,4,4,6,6-tetrachloride (TAPC) and MoO₃ as the hole-injection layer (HIL) were fabricated. MoO₃ can be expected to be a good injection layer material and thus enhance the emission performance of OLED. The highest occupied molecular (HOMO) of MoO₃ is between those of m-MTDATA or TAPC and N,N’-bis-(1-naphthyl)-N,N’-diphenyl-1,1’-biphenyl-4,4’-diamine (NPB), which reduces the hole-injection barrier and improves the luminance of the OLEDs. The current efficiency is improved compared with that of the device without the MoO₃ layer. The highest luminous efficiency of the device with 2-nm-thick MoO₃ as HIL is achieved as 5.27 cd/A at 10 V, which is nearly 1.2 times larger than that of the device without it. Moreover, the highest current efficiency and power efficiency of the device with the structure indium-tin oxide (ITO)/TAPC (40 nm)/MoO₃ (2 nm)/TcTa:Ir(ppy)₃ (10%, 10 nm)/ tris-(8-hydroxyquinoline) aluminium (Alq) (60 nm)/LiF (1 nm)/Al are achieved as 37.15 cd/A and 41.23 lm/W at 3.2 V and 2.8 V, respectively.