Novel bluish green benzimidazole-based iridium(iii) complexes for highly efficient phosphorescent organic light-emitting diodes

Abstract

Three multifluorinated benzimidazole-based iridium [Ir(III)] complexes abbreviated as 1F-Ir, 2F-Ir, and 3F-Ir were designed and synthesized. Their photoluminescent, thermal, and electrochemical properties were investigated in detail. These Ir(III) complexes exhibited strong bluish green emission with a high quantum efficiency of 0.68–0.81. Organic light-emitting diodes (OLEDs) with the simple structure of ITO/1,1-bis(4-(N,N-di(p-tolyl)amino)phenyl)cyclohexane (TAPC) (20 nm)/4,4′-N,N′-dicarbazole-biphenyl (CBP):Ir(III) complex (30 nm)/1,3,5-tris(N-phenylbenzimidazol-2-yl)benzene (TPBi) (50 nm)/8-hydroxyquinolinato lithium (Liq) (2 nm)/Al were fabricated to evaluate the potential applications of these fluorinated Ir(III) complexes. Good device performance (current efficiency: 48.0–70.1 cd A⁻¹ and external quantum efficiency: 15.6–21.7%) was achieved. In particular, OLEDs with 2F-Ir as a dopant emitter showed the best performance with a maximum current efficiency of 70.1 cd A⁻¹ and a maximum external quantum efficiency of 21.7% along with low efficiency roll-off. In this study, a very simple strategy has been reported to regulate the emitting color and improve the luminous efficiency of the Ir(III) phosphorescent emitters with great potential for practical applications in the field of OLEDs.