Improving the turn-on time of light-emitting electrochemical cells without sacrificing their stability

The effect of ionic liquids (ILs) with different intrinsic ionic conductivities on the performance of LECs consisting of the archetype Ir-iTMC bis(2-phenylpyridine)-2,2'-bipyridine-iridium(III) hexafluorophosphate, [Ir(ppy)₂bpy]PF₆, as the active electroluminescent component, was studied. Prior to the deposition of the active layer, a thin layer (100 nm) of poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS) was spin-coated to increase the reproducibility of the devices. The active layer consisted of [Ir(ppy)2bpy]PF6 mixed with one of the three different ILs at Ir-iTMC:IL molar ratios of 1:0, 1:1, and 4:1. All LECs showed a homogeneous emitting area, which together with the similar emission spectra is an indication of a high compatibility of the Ir-iTMC with the different ILs. The devices employing the IL with the highest intrinsic conductivity show efficacy decay curves that are more similar to the luminance decay curves and hence maintain a rather constant efficacy over time.