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Positional Isomeric Cyano-Substituted Bis(2-phenylpyridine)(acetylacetonate)iridium Complexes for Efficient Organic
Jia-Xun Xie1,2, Chih-Chien Lee2, Lin-Ming Huang3
1Organic Electronics Research Center, Ming Chi University of Technology, New Taipei City 24301, Taiwan.
ACS Applied Materials & Interfaces
|August 25, 2023
Summary
Researchers developed new cyano-substituted iridium complexes for efficient yellow-to-red phosphorescent organic light-emitting diodes (PhOLEDs). These materials offer a simple design strategy for high-performance PhOLEDs with reduced molecular weight.
Area of Science:
- Materials Science
- Organic Electronics
- Photochemistry
Background:
- Bis(2-phenylpyridine)(acetylacetonate)iridium [Ir(ppy)2(acac)] is a standard green emitter in phosphorescent organic light-emitting diodes (PhOLEDs).
- Developing efficient emitters for the yellow to red region remains a key challenge in PhOLED technology.
Purpose of the Study:
- To synthesize and characterize novel cyano-substituted Ir(ppy)2(acac) complexes for yellow-to-red emission.
- To investigate the effect of cyano substitution position on the electronic and photophysical properties of iridium complexes.
- To evaluate the performance of these complexes as emitters in PhOLED devices.
Main Methods:
- Synthesis of three positional isomeric cyano-substituted Ir(ppy)2(acac) complexes: Ir(3-CN), Ir(4-CN), and Ir(10-CN).
- Theoretical investigation and single-crystal X-ray diffraction analysis.
- Photoluminescence quantum yield (PLQY) and phosphorescence lifetime measurements.
- Fabrication and characterization of PhOLED devices utilizing the synthesized complexes.
Main Results:
- The synthesized complexes emit in the yellow to red region (544-625 nm).
- Cyano substitution tunes electron distribution and coordination bond length, enhancing charge transfer and reducing the energy gap.
- High PLQYs were achieved: 83% for Ir(3-CN), 54% for Ir(4-CN), and 75% for Ir(10-CN).
- The device with Ir(3-CN) showed a maximum external quantum efficiency (EQE) of 25.4%, current efficiency of 56.9 cd A-1, power efficiency of 68.7 lm W-1, and brightness of 61,340 cd m-2.
- Excellent efficiency stability was observed with minimal roll-off at high brightness.
Conclusions:
- Positional cyano substitution on the ppy ligand is an effective strategy for designing efficient yellow-to-red phosphorescent emitters.
- The developed complexes offer a simple molecular design with reduced weight for high-performance PhOLEDs.
- These findings provide a pathway for developing advanced materials for next-generation display and lighting applications.
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