Deep-Blue Phosphorescent Ir(III) Complexes with Light-Harvesting Functional Moieties for Efficient Blue and White PhOLEDs in Solution-Process

The photoluminescence (PL) efficiency of emitters is a key parameter to accomplish high electroluminescent performance in phosphorescent organic light-emitting diodes (PhOLEDs). With the aim of enhancing the PL efficiency, this study designs deep-blue emitting heteroleptic Ir(III) complexes (tBuCN-FIrpic, tBuCN-FIrpic-OXD, and tBuCN-FIrpic-mCP) for solution-processed PhOLEDs by covalently attaching the light-harvesting functional moieties (mCP-Me or OXD-Me) to the control Ir(III) complex, tBuCN-FIrpic. These Ir(III) complexes show similar deep-blue emission peaks around 453, 480 nm (298 K) and 447, 477 nm (77 K) in chloroform. tBuCN-FIrpic-mCP demonstrates higher light-harvesting efficiency (142%) than tBuCN-FIrpic-OXD (112%), relative to that of tBuCN-FIrpic (100%), due to an efficient intramolecular energy transfer from the mCP group to the Ir(III) complex. Accordingly, the monochromatic PhOLEDs of tBuCN-FIrpic-mCP show higher external quantum efficiency (EQE) of 18.2% with one of the best blue coordinates (0.14, 0.18) in solution-processing technology. Additionally, the two-component (deep-blue:yellow-orange), single emitting layer, white PhOLED of tBuCN-FIrpic-mCP shows a maximum EQE of 20.6% and superior color quality (color rendering index (CRI) = 78, Commission Internationale de L'Eclairage (CIE) coordinates of (0.353, 0.352)) compared with the control device containing sky-blue:yellow-orange emitters (CRI = 60, CIE coordinates of (0.293, 0.395)) due to the good spectral coverage by the deep-blue emitter.