Highly efficient iridium(iii) phosphors with a 2-(4-benzylphenyl)pyridine-type ligand and their high-performance organic light-emitting diodes

Abstract

A series of new cyclometalated iridium(III) complexes containing a methyl or a trifluoromethyl substituted 2-(4-benzylphenyl)pyridine molecular framework have been synthesized and characterized. All these complexes are amorphous and possess excellent thermal stabilities. Arising from the propensity of the tetrahedral geometry of the CH2 moiety in the benzyl group, this could make the metal complexes less crystalline, attain more morphologically stable thin-film formation and reduce the triplet–triplet annihilation process, especially in the solid state. The optical, electrochemical, and photo- and electrophosphorescence traits of these iridium(III) phosphors have been studied in terms of the electronic nature of the pyridyl ring substituents. Electrophosphorescent organic light-emitting diodes (OLEDs) with attractive device performance can be fabricated based on these materials. The best electroluminescent (EL) performance can be obtained with a maximum current efficiency (ηL) of 76.3 cd A−1, a maximum power efficiency (ηP) of 51.1 lm W−1, a maximum external quantum efficiency (ηext) of 21.4% and a pure green CIE color coordinates of (0.27, 0.64). The present work provides a simple way to enhance the OLED performance by simply modifying the molecular design of the benchmark emitters, which show great potential for application in multicolor displays.