High performance blue-green and green phosphorescent OLEDs based on iridium complexes with N^C^N-coordinated terdentate ligands

Abstract

Highly efficient phosphorescent organic light-emitting diodes (PhOLEDs) based on two iridium complexes constructed by the N^C^N-coordinated terdentate ligands (also called pincer ligands) have been achieved. They exhibit high peak power efficiency (PE) and external quantum efficiency (EQE) values of 35.5 lm W⁻¹ & 15.8% for blue-green emission, 47.4 lm W⁻¹ & 16.7% for green emission, which maintain the high levels of 19.2 lm W⁻¹ & 14.5% and 30.6 lm W⁻¹ & 16.1% at rather high and practical luminance of 500 cd m⁻² with low driving voltages of less than 6 V. These values show almost a twofold enhancement over the most efficient PhOLEDs based on pincer iridium complexes ever reported. Here, the appropriate selection of a prominent electron-transport molecule TPBi as a host to match the dopant molecules (1 or 2) that possess sufficient hole-transport ability is critical in the remarkable EL-performance improvement compared to previous reports. We will present a comprehensive investigation that not only encompasses the conventional thermal, photophysical and electrochemical properties of both complexes, but also emphatically studies the charge carrier injecting/transporting and electroluminescent (EL) characteristics of two phosphorescent emitters doped in different hosts.