Highly Efficient Solution-processed Organic Light-Emitting Diodes Based On Small Molecular Materials

Organic light-emitting diodes(OLEDs)have received immense attraction for their potential in flexible displays and light sources.Almost all OLED devices are prepared via vacuum evaporation and solution processes,but the former generally requires more cost due to its complex production system,which hinders the application of OLEDs.So,it is necessary to study low-cost solution process for its commercialization.As it is well known,unlike phosphorescence materials consisting of rare metals such as iridium or polymers difficult to be purified,purely organic traditional fluorescence and thermally activated delayed fluorescence(TADF)molecules with small energy gaps can be easily synthesized with low cost for light-emitting materials in solution-processed OLED devices.However,there are few high-efficiency solution-processed all-fluorescence white OLEDs reported especially utilizing small molecules up to now,which proves the necessity of our work.A solution-processed non-doped device structure was designed and utilized for hightriplet TADF molecules.With such a device structure,the exciton quenching which generally hinders the performance of devices at high current density in solution-processed blue OLEDs can be greatly suppressed,leading to a maximum external quantum efficiency(EQE)of 12.8% for the blue light-emitting device based on a blue emitter 2,7-(bis(9,9-dimethylacridin-10(9H)-yl)9,9-diphenyl-9H-thioxanthene-10,10-dioxide(DMAC-DPTX).Efficient white OLEDs were also fabricated based on the blue emitter DMAC-DPTX by introducing a yellow emitter(2-(4-phenoxa-zinephenyl)thianthrene-9,9',10,10'-tetraoxide)(PXZDSO2)as a complementary dopant.Notably,a maximum EQE of 19.4% was achieved in the same device structure of the blue light-emitting device by solely doping PXZDSO2 into the blue emitter DMAC-DPTX.It is also the best peformance among the reported solutionprocessed all-fluorescence white OLEDs up to now.To achieve high efficiency and high color-rendering index(CRI)white OLEDs at the same time,a red fluorescence material 5,10,15,20-tetraphenylbenzo[5,6]indeno [1,2,3cd]benzo[5,6]indeno[1,2,3-lm]perylene(DBP)was utilized to fabricate threecomponent single-emitting-layer white OLEDs.A maximum EQE of 16.4% with a CRI of 72 and a maximum EQE of 11.0% with a CRI of 88 were achieved,both of which are the highest efficiencies for the white OLEDs in the corresponding CRI ranges,respectively.