Red ionic iridium-based transition metal complex light-emitting electrochemical cells (iTMC-LECs) with emission centered at ca. 650 nm, maximum efficiency of 0.3%, maximum brightness above 650 cd m-2, and device lifetime well above 200 and 33 h at brightness levels of 10 and 210 cd m-2, respectively, are realized by the introduction of a p-type polymer interface to the standard design of [Ir(ppy)2(pbpy)]+[PF6]- (Hppy = 2-phenylpyridine, pbpy = 6-phenyl-2,2'-bipyridine) iTMC-LEC. The unexpected color shift from yellow to red is studied in detail with respect to operation conditions and material combination. The experimental data suggest that either exciplex formation or subordinate, usually suppressed optical transitions of the iTMC might become activated by the introduced interface, causing the pronounced red shift of the peak emission wavelength.
Keywords: iTMC; interface effect; iridium; light-emitting electrochemical cell; red emission.