Optical outcoupling enhancement in organic light-emitting diodes using a gradually varying refractive index dielectric structure

초록

To provide a practical method to enhance the optical outcoupling of organic light-emitting diodes (OLEDs), we propose the use of a gradual refractive index dielectric (GRID) structure. The GRID structure of the sequentially varying WO3 : CaF2 composition ratio was fabricated using a sequential codeposition method. Optical outcoupling from surface plasmon polariton (SPP) modes is promoted owing to the large refractive index of WO3, and the formation of waveguide modes in the GRID structure is impeded owing to the irregular surface morphology of CaF2. The efficiency of the OLEDs was improved by more than 20% using the GRID multicathode OLED (MC-OLED) structure, without requiring an additional patterning process. In addition, the emission spectra remained almost unchanged following the introduction of the GRID MC structures, and the angular distribution of luminance became similar to that of Lambertian emission. Owing to the high performance and simple low-cost fabrication processes, the outcoupling enhancement method using a GRID structure is expected to be a practical solution to improving the luminous efficiency of OLEDs, with applications including high-performance mobile display devices and large-area televisions. (C) 2015 The Japan Society of Applied Physics

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