Highly efficient organic light-emitting devices employing an ultrathin non-doped phosphorescence emitter within a thermally activated delayed fluorescence interface exciplex

Abstract

High-efficiency phosphorescent organic light-emitting devices (PHOLEDs) based on a doping-free host-guest luminous system have been fabricated. The highly simplified design philosophy puts emphasis on an orange ultrathin non-doped phosphorescent nanolayer (UNPN, < 1nm) inserted in an interface exciplex-forming electron donor/acceptor (D/A) planar structure. Two kinds of hole transporting materials and one electron transporting material are introduced as electron donors and acceptor, respectively, for the modulation of exciplex property and emission process. Meanwhile, the UNPN thickness has been optimized to simultaneously realize efficient exciplex formation and complete energy transfer from exciplex to phosphor. As a result, PHOLEDs based on 4,4′,4′′-tris(N-carbazolyl)-triphenylamine/bis(4,6-(3,5-di-(3-pyridyl)phenyl))-2-methylpyrimidine interface exciplex and a 0.3nm-thick UNPN have achieved a power efficiency of 53.1lm/W, a luminance efficiency of 53.3cd/A and an external quantum efficiency of 19.5%, respectively. The high efficiencies are attributed to the elimination of leakage current across D/A interface, efficient reverse inter-system crossing of exciplex and complete host-guest energy transfer, which significantly alleviate triplet energy loss through the non-radiative triplet states of exciplex.