Toshitaka NAKAMURA^1,2, Hironaka FUJII², Noriyuki JUNI² and Naoto TSUTSUMI^1*

¹Department of Polymer Science and Engineering, Kyoto Institute of Technology, Matsugasaki, Sakyo-ku, Kyoto 606-8585, Japan
²Core Technology Center, Nitto Denko Corporation, 1-1-2 Shimohozumi, Ibaraki, Osaka 567-8680, Japan

(Received November 8, 2005; Accepted December 28, 2005)

To improve light extraction from organic electroluminescent (EL) devices, we introduced a diffusive substrate with 25 μm thickness consisting of high refractive index resin and scattering particles. It is expected that the diffusive substrate with high refractive index matrix converts the waveguided emission into external emission from both glass substrate and indium–tin-oxide/organic layer. We used the ray tracing method to optimize the scattering effect and to verify the coupling out effect of the diffusive high refractive index substrate. With the use of the ray tracing calculation, an increase in the external emission up to a factor of 2.7 was expected compared to use of a common glass substrate. Experimentally, the coupling out effect of the diffusive high refractive index substrate strongly depended on the thickness of electron transporting layer (ETL) due to the well-known interference effect. The current efficiency increased by a factor of 1.3 for an organic EL device with a 60-nm-thick ETL and by a factor of 6.8 for one with a 120-nm-thick ETL.

Key words: organic electroluminescent device, high refractive index, scattering particle, wave-guided light

^*To whom all correspondence should be addressed.