Efficient Organic Light‐Emitting Diodes based on Sublimable Charged Iridium Phosphorescent Emitters

Abstract

AbstractThe synthesis and characterization of two new phosphorescent cationic iridium(III) cyclometalated diimine complexes with formula [Ir(L)2(N‐N)]+(PF6–) (HL = (9,9‐diethyl‐7‐pyridinylfluoren‐2‐yl)diphenylamine); N‐N = 4,4′‐dimethyl‐2,2′‐bipyridine (1), 4,7‐dimethyl‐1,10‐phenanthroline (2)) are reported. Both complexes are coordinated by cyclometalated ligands consisting of hole‐transporting diphenylamino (DPA)‐ and fluorene‐based 2‐phenylpyridine moieties. Structural information on these heteroleptic complexes has been obtained by using an X‐ray diffraction study of complex 2. Complexes 1 and 2 are morphologically and thermally stable ionic solids and are good yellow phosphors at room temperature with relatively short lifetimes in both solution and solid phases. These robust iridium complexes can be thermally vacuum‐sublimed and used as phosphorescent dyes for the fabrication of high‐efficiency organic light‐emitting diodes (OLEDs). These devices doped with 5 wt % 1 can produce efficient electrophosphorescence with a maximum brightness of up to 15 610 cd m–2 and a peak external quantum efficiency of ca. 7 % photons per electron that corresponds to a luminance efficiency of ca. 20 cd A–1 and a power efficiency of ca. 19 lm W–1. These results show that charged iridium(III) materials are useful alternative electrophosphors for use in evaporated devices in order to realize highly efficient doped OLEDs.