Enabling a bright orange–red emission with a high EQE with a seven-member-ring based fluorescent emitter with a matching host

Abstract

A bright orange–red organic light-emitting diode (OLED) with an extraordinarily high external quantum efficiency (EQE) was achieved by using a seven-member-ring based fluorescent emitter with a matching host. The emitter, 3-(N,N-diphenylamino)-7-(β,β-dicyanoethenyl)-5,5-spirofluorenyl-5H-dibenzo[a,d]-cycloheptene, was composed of a spirally configured cis-stilbene/fluorene moiety with an ambipolar character, and the matching host was 1-butyl-9,10-naphthalene-anthracene (BANE). An orange–red emission peaking at 617nm with an EQE continuously rolling up to its observable maximum luminance was obtained as a 1.5wt% of the red emitter was doped into the BANE host. For examples, the EQEs were increased from 5.01±0.015% to 5.76±0.02%, and 6.43±0.04% as the luminance was increased from 10,000 to 15,000 and 20,000cd/m2, respectively. The high efficiency at high brightness as well as an unusual efficacy roll-up may be attributed to both the efficiency-effective device architectural factors, including low injection barriers, balanced carrier injection, effective host-to-guest energy transfer, and effective exciton generation on both host and guest, and the ambipolar emitter that showed an increasing balance in carrier injection as the applied voltage continued to increase.