Realizing efficient red thermally activated delayed fluorescence organic light-emitting diodes using phenoxazine/phenothiazine-phenanthrene hybrids

Abstract

Abstract The development of highly efficient red and deep red organic emitting materials with nature of thermally activated delayed fluorescence (TADF) lags far behind the exploitation of blue and green emitters. Two novel TADF emitters, 7,10-bis(phenoxazine)-2,3-dicyanopyrazino phenanthrene (PXZ-DCPP) and 7,10-bis(phenothiazine)-2,3-dicyanopyrazino phenanthrene (PTZ-DCPP), were designed and synthesized by employing phenoxazine (PXZ) or phenothiazine (PTZ) as the electron donor unit and 2,3-dicyanopyrazino phenanthrene (DCPP) as the electron acceptor unit. Small energy differences between the lowest singlet and triplet excited states and relatively long fluorescence lifetimes were obtained. Organic light-emitting diodes (OLEDs) containing PXZ-DCPP and PTZ-DCPP demonstrated high maximum external quantum efficiencies (EQEs) of 17.4% and 12.3% with maximum power efficiencies of 27.8 and 8.1 lm/W, respectively. Orange and red electroluminescence spectra centered at 608 and 640 nm were achieved with Commission Internationale de L'Eclairage coordinates of (0.56, 0.43) and (0.62, 0.36), respectively. More importantly, the two TADF OLEDs exhibited slight efficiency roll-off with the EQEs of 12.9% and 6.1% at a luminescence of 1000 cd/m2.