Abstract
Metal oxides are intensively used for multilayered optoelectronic devices such as organic light-emitting diodes (OLEDs). Many approaches have been explored to improve device performance by engineering electrical properties. However, conventional methods cannot enable both energy level manipulation and conductivity enhancement for achieving optimum energy band configurations. Here, we introduce a metal oxide charge transfer complex (NiO:MoO3-complex), which is composed of few-nm-size MoO3 domains embedded in NiO matrices, as a highly tunable carrier injection material. Charge transfer at the finely dispersed interfaces of NiO and MoO3 throughout the entire film enables effective energy level modulation over a wide work function range of 4.47 – 6.34 eV along with enhanced electrical conductivity. The high performance of NiO:MoO3-complex is confirmed by achieving 189% improved current efficiency compared to that of MoO3-based green OLEDs and also an external quantum efficiency of 17% when applied to blue OLEDs, which is superior to 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile-based conventional devices.
Highlights
Metal oxides are intensively used for multilayered optoelectronic devices such as organic light-emitting diodes (OLEDs)
Through interaction between the matrix material and the dopant layer, the nonidentical band position of the two materials promotes charge transfer, which, in turn, modifies the energy level at the interface of the two materials of the surface charge transfer doping (SCTD) system. This phenomenon is localized to a 10 nm thick area at the interface of the bilayer, and is unsuitable for multilayered optoelectronic applications where the charge flows vertically to the charge transfer region of the SCTD system
We evaluated HATCN besides nickel oxide (NiO):MoO3-complex as a hole injection layer (HIL), which is widely used in various OLED structures, to clarify the generality of the NiO:MoO3-complex
Summary
Metal oxides are intensively used for multilayered optoelectronic devices such as organic light-emitting diodes (OLEDs). Metal oxide thin films are considered an attractive material for various functional applications because of their favorable energy band structure, excellent processability, and high stability[1,2,3] This material system is intensively applied to multi-layered optoelectronic devices such as quantum-dot light-emitting diodes (QLEDs) and organic light-emitting diodes (OLEDs) for ensuring efficient charge transport and charge injection into the emission layer[4,5,6,7,8,9,10]. NiO:MoO3-complex is applied to an additional optoelectronic configuration of blue phosphorescent OLEDs, and their high capability and generality is verified on the basis of excellent performance (32.6 cd A−1 and 17% external quantum efficiency (EQE)), which is even higher than that of device using 1,4,5,8,9,11-hexaazatriphenylene-hexacarbonitrile (HATCN)
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