Using an embedded nanocomposite scattering film for increasing out-coupling of white phosphorescent organic light-emitting devices

For the lighting purpose, white organic light-emitting devices (OLEDs) need to be operated at a high current density to ensure an ample flux, which will lead the limited lifespan of the device. This situation could be improved through diversified light-extraction methods. In this study, transparent photoresist mixed with titanium oxide (TiO2) nanoparticles of different sizes could be utilized to form an internal extraction structures between the indium-tin-oxide and glass substrate and thereby the out-coupling efficiency of white OLEDs could be significantly improved by this sophisticated device architecture engineering. The high refractive index of TiO2 is essentially operative for increasing the refractive index of nanocomposite film and thus diminishing the total internal reflection between the interfaces. In addition, the nanoparticles served scattering function to multiply the ratio of the substrate and radiation modes. By employing nanocomposite substrate with mixed dual-sized nanoparticles, we obtained external quantum efficiencies of the white phosphorescent OLEDs that were about 1.6 times higher than that of the control device at the high luminescence of 104 cd/m(2).