Organic Light-Emitting Diodes Based on a Solution-Processable Benzimidazole-Functionalised Cationic Iridium Complex

A cationic iridium(iii) complex with formula [Ir(ppy)2(pybmz)]+(PF6)– (ppy = 2-phenylpyridine; pybmz = 2-(pyridin-2-yl)-N-hexylbenzimidazole) was synthesised. The photoluminescence spectrum of the complex showed an orange–red emission peak at 590 nm with a quantum efficiency of 18 % and a luminescence lifetime of 1.2 µs in solid state. The complex was used as a phosphorescent dopant in light-emitting diodes with the configuration ITO/PEDOT : PSS(50 nm)/PVK (70) : PBD (30) : complex (x wt-%, x = 5, 20, 50, 100)(75nm)/TPBI(50nm)/Ba(4 nm)/Al(150 nm) [ITO = indium tin oxide; PEDOT = poly(ethylenedioxythiophene); PSS = poly(styrene sulfonic acid); PVK = polyvinylcarbazole; PBD = 5-(4-tert-butylphenyl)-2-(bi-phenyl-4-yl)-1,3,4-oxadiazole; TPBI = 1,3,5-tris-(2-N-phenylbenzimidazolyl) benzene]. The best device performances were obtained for the non-doped (100 wt-%) material, with an external quantum efficiency of 5.6 %, a luminous efficiency of 9.3 cd A–1, and a power efficiency of 3 lm W–1. High brightness of 8700 cd m–2 and luminous efficiency of 8 cd A–1 were realised at a current density of 110 mA cm–2.