Merits of narrow spectral blue fluorescence emitters in strong micro-cavity top emission OLEDs

Abstract

The top emission organic light emitting diode (TEOLED) structure can realize the high efficiency and high color purity through the micro-cavity effect. The characteristics of TEOLED are enhanced by improving the electrodes structures or designing cavities through organic layers. Apart from these factors, the optical characteristic of the emitting material is another very important aspect to improve the TEOLED characteristics. In the present study, we investigated the influence of the narrow full width at half maximum (FWHM) of emitter on the blue light emitting device characteristics through the simulations and experiments. We analyzed the radiance, current efficiency, and blue index characteristics of TEOLED using several emitters having different FWHM values. As the FWHM became narrower, the radiant out-coupling spectrum could overlap sufficiently with original one; so the radiance was improved, but the current efficiency was affected due to the decrease in luminosity factor. Additionally, the blue index value is an important in TEOLED structure, as display applications uses it. TEOLED having the same emission peak value, the narrower FWHM emitter is advantageous in terms of the blue index because of the improved color purity. The narrower the FWHM, the just noticeable color difference is low. The color stability according to the viewing angle is also improved. From the optical simulation results, the optimum condition of the emitter FWHM varies from 14 to 16 nm and the emission peak shifts from 460 to 462 nm. With these emitter conditions, the TEOLED device has excellent color purities and the highest blue efficiency characteristics. • Analyzes the efficiency of TEOLED device according to the FWHM of the blue emitter. • Efficiency is analyzed through optical simulation. • The viewing angle characteristics in terms of the FWHM of the blue emitter were also observed. • In order to obtain a TEOLED device with outstanding characteristics, we suggest the optimal conditions of wavelength and FWHM of blue emitter.