5 years ago

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

Deep-Blue Phosphorescent Ir(III) Complexes with Light-Harvesting Functional Moieties for Efficient Blue and White PhOLEDs in Solution-Process
Vijaya Gopalan Sree, Myungkwan Song, Woosum Cho, Athithan Maheshwaran, Ho-Yeol Park, Yeong-Soon Gal, Sung-Ho Jin, Ganguri Sarada
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. Highly efficient deep-blue phosphorescent Ir(III) complexes with light-harvesting groups are introduced for blue and white phosphorescent organic light-emitting diodes. Intramolecular energy transfer from a high triplet energy donor (mCP-Me) to the Ir(III) complex (tBuCN-FIrpic) is found to increase the photoluminescence efficiency of tBuCN-FIrpic-mCP. Therefore, tBuCN-FIrpic-mCP shows high external quantum efficiency of 18.2% with intense blue coordinates (0.142, 0.181) in a solution-process.

Publisher URL: http://onlinelibrary.wiley.com/resolve/doi

DOI: 10.1002/adfm.201701002

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