Highly efficient blue fluorescent organic light-emitting diodes with a high emitter/host ratio

Abstract

Blue organic light emitting diodes are made based on 4,4′-bis(9-ethyl-3-carbazovinylene)-1,1′-biphenyl (BCzVBi) as a fluorescent emitter mixed with two charge transport hosts, 4,4′-bis(carbazol-9-yl)biphenyl and Bis[2-(2-hydroxyphenyl)-pyridine]beryllium. It is found that the device efficiency increases as BCzVBi concentration increases. An extremely high 6.1% external quantum efficiency (EQE) with Commission Internationale de L'Eclairage coordinate of (0.18, 0.31) is obtained when the BCzVBi concentration reaches 50 wt. %, which is exceedingly high above a typical 1-2 wt. % concentration for typical fluorescent emitters. The 6.1% EQE is also much higher than the expected 3% value calculated using the prevailing theorem.