Influence of Phosphine Oxide containing Symmetrical and Asymmetrical Ancillary Ligands on Solution-Process Phosphorescence Organic Light-Emitting Diode Efficiency and Life Time.
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In order to achieve longer stability with high efficiency of organic light-emitting diodes (OLEDs), we designed and synthesized two new 2-phenylpyridine based Ir(III) dopants and a suitable host for the fabrication of green phosphorescent OLEDs (PHOLEDs). The solution-process green devices using bis[5-ethylhexyl-8-trifluoromethyl-5H-benzo(c)(1,5)naphthyridin-6-one](dipyridi nylphosphinate)iridium(III) (sym-Ir1) as dopant, (4'-(9H-carbazol-9-yl)-[1,1'-biphenyl]-4-yl)di-o-tolylphosphine oxide (m-CBPPO1) and TPBi as host. The optimized devices show excellent electroluminescence performances with maximum current efficiency (CE) of 68.72 cd/A, a maximum external quantum efficiency (EQEmax) of 20.82% with a notable (0.29, 0.62). The sym-Ir1 showed comparatively better stability compared it counterpart. We believe that the presence of undesirable isomers of the asym-Ir2 is the cause to the effective degradation of the solution processed devices.