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 power efficiency at 100 cd/m2 as a sky-blue emitter, 1-((9,9-diethyl-9H-fluoren-2-yl)ethynyl)pyrene, with CIExy of (0.19, 0.24) 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 be resulted from a low doping concentration to prevent bathochromic shift due to emitter segregation, a polarity matching host to further disperse the emitter, and a proper host and guest energy level paring that enables exciton to generate on host to trigger short wavelength emission. Furthermore, the host is capable of generating excitons with higher energy to facilitate triggering emission with a shorter wavelength. The high efficiency may be attributed to the low doping concentration preventing concentration-quenching caused efficiency roll-off, the exciton generated on host facilitating the occurrence of the efficiency 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 whose molecular structure is free of steric hindrance.