The use of a polarity matching and high-energy exciton generating host in fabricating efficient purplish-blue OLEDs from a sky-blue emitter

Abstract

We reveal in this communication a new finding regarding the use of a sky-blue emitter to generate purplish-blue emission from organic light emitting diodes (OLEDs) with a polarity matching and high-energy exciton generating host. The resulting device exhibits CIExy coordinates of (0.155, 0.063) and a 3.5% external quantum efficiency, with a 1.2 lm W−1 power efficiency at 100 cd m−2 as a sky-blue emitter, 1-((9,9-diethyl-9H-fluoren-2-yl)ethynyl)pyrene with CIExy of (0.190, 0.241) is doped into a host of 4,4′-bis(9-carbazolyl)-biphenyl, for example. The resulting purplish-blue emission enables a greater than 100% color saturation. The extraordinarily marked blue-shift may result from a low doping concentration to prevent bathochromic shift due to emitter segregation, a polarity matching host to further disperse the emitter, and an efficient host and guest energy level pairing that enables excitons to be generated on the host to trigger short wavelength emission. Furthermore, the host is capable of generating excitons with higher energy to facilitate the triggering of emission with a shorter wavelength. The high efficiency may be attributed to the low doping concentration preventing efficiency roll-off caused by concentration-quenching, the excitons generated on the host facilitating the occurrence of the effective host-to-guest energy transfer, and the employed host possessing an effective host-to-guest energy transfer effect. Notably, the new approach also works for other light-blue emitters in yielding a highly desirable deep-blue light, provided their molecular structure is free of steric hindrance.