Efficient organic light-emitting diodes with low efficiency roll-off at high brightness using iridium emitters based on 2-(4-trifluoromethyl-6-fluoro phenyl)pyridine and tetraphenylimidodiphosphinate derivatives

Add time:07/15/2019    Source:sciencedirect.com

Using 2-(4-trifluoromethyl-6-fluorophenyl)pyridine (tfmfppy) as the cyclometalated ligand and tetraphenylimidodiphosphinate (tpip) derivatives as ancillary ligands, three iridium complexes (1: Ir(tfmfppy)2tpip; 2: Ir(tfmfppy)2ftpip, ftpip = tetra(4-fluorophenyl)imidodiphosphinate; 3: Ir(tfmfppy)2tfmtpip, tfmtpip = tetra(4-trifluoromethylphenyl)imidodiphosphinate) showing phosphorescence at 514, 513 and 508 nm in CH2Cl2 were synthesized, respectively. By using these complexes as emitters, the organic light emitting diodes with the concise configuration of indium tin oxides/1,1-bis(4-(di-p-tolyl-amino)phenyl)cyclohexane (60 nm)/1 or 2 or 3: bis[3,5-di(9H-carbazol-9-yl)phenyl]di-phenyl silane (8 wt%, 30 nm)/1,3,5-tri(1-phenyl-1H-benzo[d]imidazol-2-yl)phenyl (90 nm)/lithium fluoride (1 nm)/aluminium (100 nm) showed bright green light with maximum luminance higher than 40 000 cd m−2. The maximum current efficiency (ηc) values for 1, 2 and 3 based devices (GIr1, GIr2 and GIr3) were 77.49, 66.57, and 53.26 cd A−1 at relatively high brightness of 8025, 5286 and 5169 cd m−2, respectively. In addition, the efficiency roll-off ratios from the peak efficiency to the brightness of 10 000 cd m−2 are less than 10% for all the devices. We believe that the good electron mobilities of the phosphorescent emitters lead to the high devices efficiency and low efficiency roll-off. The results suggest that these complexes have potential application in organic light emitting diodes.

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