Small dose of phosphorescent dopant enabling high efficiency and bright solution-processed sky-blue organic light-emitting diodes

Abstract

In this work, we demonstrate the simultaneous use of thermally activated delayed fluorescence (TADF) material and a small dose of phosphorescent material to construct TADF-phosphorescent mixed emitting system, which enables the OLED exhibiting high device performance. To achieve this, a blue TADF material, 10,10'- (4,4′-Sulfonylbis (4,1-phenylene)) bis (9,9-dimethyl-9,10-dihydroacridine) (DMAC-DPS), and a conventional blue phosphor with similar emission color to DMAC-DPS, Bis [2-(4,6-difluorophenyl) pyridinato-C2, N] (picolinato) iridium (III) (FIrpic), are incorporated together into 1,3-Bis(carbazol-9-yl) benzene (mCP) host to constructed the mixed emitting system. The device has achieved the maximum current efficiency of 21.1 cd/A with FIrpic concentration of 1%; meanwhile, the luminance of the device has also been improved. There merits are superior to the optimized TADF OLED and the optimized phosphorescent OLED based on 16% FIrpic in device efficiency. In view of the expensive price of phosphorescent materials, the strategy presented here will greatly reduce the material cost without the cost of device performance. Through investigations on the energy transfer process and the film morphology in the mixed emitting system, the main cause of the improvement has been unveiled. The study may provide a simple but effective strategy to achieve low-cost, high-performance solution-processed OLEDs.