Extremely low efficiency roll-off in vacuum- and solution-processed deep-red/near-infrared OLEDs based on 1,8-naphthalimide TADF emitters

Abstract

Deep-red to near-infrared (DR-NIR) organic light-emitting diodes (OLEDs) based on purely organic thermally activated delayed fluorescence (TADF) emitters usually suffer from serious efficiency roll-offs. Herein, a series of 1,8-Naphthalimide-derivatives-based wedge-shape emitters, 2DN and 2PN, were designed and synthesized by adopting multiple donor units and isopropyl modification strategies. 2DN and 2PN exhibited strong DR-NIR TADF in the range 646–755 nm in toluene and films. The OLEDs, fabricated by both vacuum-deposition and solution-processed methods, all exhibited desired DR-NIR electroluminescence in the range 629–701 nm, and significantly reduced efficiency roll-offs (8.4% for 2DN and near zero for 2PN at 100 cd m−2), which benefit from short delayed lifetime (36.4 us for 2DN and 14.0 us for 2PN) and negligible π-π stacking in aggregation states. It indicates that the efficiency roll-offs of DR-NIR TADF OLEDs can be greatly reduced by designing emitters with appropriate design of molecular structures.