Highly efficient organic light-emitting diodes employing the periodic micro-structured ITO substrate fabricated by holographic lithography.

The optical waveguide effect limits strongly the light out-coupling efficiency in organic light-emitting diodes (OLEDs). Patterning the transparent ITO anode on the substrate is a potential way to weaken the optical waveguide effect and enhance the light-emitting efficiency of OLEDs. Herein, the one-dimensional (1D) and two-dimensional (2D) periodic patterned ITO/glass substrates have been successfully fabricated by using the holographic lithography technology and used to fabricate highly efficient OLEDs. The periodic micro-structured ITO layer could manipulate the total internal reflection at the organic/ITO interfaces and enhance the scattering effect so as to improve the light out-coupling efficiency. The effect of different micro-structured ITO layers on the light-emitting efficiency was investigated in a kind of orange phosphorescent OLEDs based on the m-MTDATA:Ir(Flpy-CF 3) 3 /TmPyPB emissive layer. The orange OLEDs employing the 1D grating and 2D lattice patterned ITO/glass substrates show the external quantum efficiencies (EQEs) of 25.12% and 29.61%, respectively. The orange OLEDs fabricated with the 2D hole patterned ITO glass substrate demonstrate the best light-emitting performance with a current efficiency of 100.55 cd A−1, an EQE of 31.39% and a power efficiency of 121.50 lm W−1, respectively. The 1D grating and 2D patterned ITO microstructures have been successfully fabricated with the holographic lithography. The phosphorescent OLEDs employing the periodic patterned ITO/glass substrate improve the light out-coupling leading to signigicantly increased light-emitting efficiency. A power efficiency of 121.50 lm W−1 is achieved for yellow phosphorescent OLEDs employing the 2D hole-patterned ITO/glass substrate. Image 1 • The 1D and 2D patterned ITO/glass substrate via holographic lithography enhances the outcoupling of emitted light from the device structure. • The light-emitting efficiencies are greatly increased by using the patterned ITO/glass substrate. • A power efficiency of 121.50 lm W−1 and an external quantum efficiency of 31.39% are achieved for yellow phosphorescent OLEDs employing the 2D hole-patterned ITO/glass substrate. [ABSTRACT FROM AUTHOR]