Highly phosphorescence iridium complexes and their application in organic light-emitting devices

Area of Science:

• Organometallic Chemistry
• Materials Science
• Photophysics

Background:

• Iridium(III) complexes are extensively studied for their photoluminescent properties.
• Tuning the electronic structure of iridium(III) complexes is crucial for achieving desired emission colors and efficiencies.
• Developing highly efficient phosphorescent emitters is key for next-generation organic light-emitting devices (OLEDs).

Purpose of the Study:

• To synthesize and characterize a new series of iridium(III) mixed ligand complexes.
• To investigate the photophysical properties, including emission spectra and quantum yields.
• To evaluate the performance of these complexes in organic light-emitting devices.

Main Methods:

• Synthesis of four iridium(III) mixed ligand complexes: TBA[Ir(ppy)2(CN)2] (1), TBA[Ir(ppy)2(NCS)2] (2), TBA[Ir(ppy)2(NCO)2] (3), and [Ir(ppy)2(acac)] (4).
• Characterization using UV-vis absorption, emission spectroscopy, IR, NMR, and cyclic voltammetry.
• Fabrication and testing of organic light-emitting devices (OLEDs) using complex 4 as an emitter.

Main Results:

• The complexes exhibit tunable lowest energy MLCT transitions from 463 to 494 nm.
• Emissions were observed in the blue, green, and yellow regions of the visible spectrum.
• Unprecedented phosphorescence quantum yields of up to 97% and excited-state lifetimes of 1-3 microseconds were achieved.
• Complex 4 demonstrated a maximum external quantum efficiency of 13.2% and a power efficiency of 37 lm/W in an OLED device.

Conclusions:

• The high quantum yields are attributed to an increased energy gap between the triplet emitting state and the deactivating e(g) level, achieved through ligand selection.
• The developed iridium(III) complexes are promising candidates for highly efficient phosphorescent emitters in OLED applications.
• The study highlights the importance of ligand field strength in optimizing the photophysical properties of iridium(III) complexes.