Oxadiazol Based Small Molecule Electron Transporting Materials For Solution-Processed OLED And Their Properties

Owing to the potential applications on the fields of large-size flexible displays and solid-state lighting sources,organic light emitting diodes?OLEDs?have attracted much attention.Comparing to the conventional vacuum evaporation techniques,solution-processed OLEDs are more compatible with the applications of large-size flexible displays and solid-state lighting sources,because of the more convenient manufactory,low cost and easier to make large area roll-to-roll manufacturing processes.The most emitters are oil soluble,and the ETLs?electron transporting layers?are on the top of them.To protect the emitting layer,it is necessary to study alcohol-soluble electron transporting material.In this work,two novel alcohol-soluble ETMs?electron transporting materials?with similar structure are designed and synthesized,then the compounds are characterized by nuclear magnetic resonance,high resolution mass spectrum,element analysis and Fourier transfer infrared spectra.Utilizing ultraviolet-visible spectra,currency-voltage curves and phosphorescent spectra,energy level?3.72 eV and 3.65eV?,LUMO?Lowest Unoccupied Molecular Orbital??-2.52 eV and-2.44 eV?and triplet energy?2.79 eV and 2.66 eV?of PhOXDPO and Ph2OXDPO were calculated respectively.Gaussian simulation is taken to prove the existence of the insulation linkage by intramolecular P=O bond,which is compliant with the charge-exciton separation mode.By thermogravimetric analysis and differential scanning calorimetry,the decomposition temperature?247?and 408??and the glass transition temperature?117?and 151??of diphenyl?4-?5-phenyl-1,3,4-oxadiazol-2-yl?phenyl?phosphine oxide?PhOXDPO?and??1,3-phenylenebis?1,3,4-oxadiazole-5,2-diyl??bis?4,1-phenylene??bis?diphenylphosphine oxide??Ph2OXDPO?are measured,which have showed good thermal stability of target molecules.X-ray diffraction spectra implies that the film·s formed by spin-coating are featureless,and atomic force microscope results suggest that the thermal stability of film·s are good.Alcohol solubility study exhibits that the solubility of target compounds in isopropanol and n-butanol are good.The space-charge-limited currency electron mobility by carrier-only devices is afforded.The electron mobility of PhOXDPO and Ph2OXDPO is as high as 6.6×10^-4 cm²·V^-1·s^-1 and 6.0×10^-4 cm²·V^-1·s^-1.Based on target compounds,red,green and blue OLEDs are fabricated,which shows that PhOXDPO and Ph2OXDPO are able to apply on full-color OLEDs as ETMs.Green phosphorescent OLEDs are optimized with the emitter of Host2:IrG=95:5.The device based on PhOXDPO shows maximum current efficiency of 49.503 cd·A^-1.And on the luminance of 1000 cd·m^-2,the efficiency roll-off is only 1.49%.OLEDs utilizing Ph2OXDPO as ETLs also achieves high efficiency and low roll-off.Comparing to no-ETLs control device,OLEDs based on TPBI by vacuum evaporation and Bphen by solution process,inducing target compounds as alcohol soluble ETMs can increase the devices efficiency greatly and lower down the roll-off.With higher electron mobility,lower HOMO value and higher triplet energy,PhOXDPO is a better ETMs than Ph2OXDPO.