Carbazole derivatives with pyridinium ion as emitters for light-emitting electrochemical cells

Abstract

Light-emitting electrochemical cells (LEEC) are relatively easy-to-fabricate thin-film lighting devices. Therefore, LEECs have been already successfully used in high-end smart lighting applications such as light-emitting clothes and emissive textiles, rollable and stretchable wallpaper-like lamps, and biocompatible light sources for in vivo or epidermal medical devices. However, most of the LEECs utilize ionic metal complexes as emitters that consist of the rear element Iridium. Ionic small molecules (SM) as light emitters could be a better solution to the low-cost device. In the work, we have investigated purely organic ionic compound that could exhibit aggregate induced emission. The compounds consist of the carbazole group and pyridinium ion as a cation. Perchlorate was used as an anion. Emission spectra, fluorescence kinetics and photoluminescence quantum yield (PLQY) were measured in polymer doped thin films. Polymethyl methacrylate (PMMA) was used as an additive. Photoluminescence quantum yield is 73% in powder and 45% in the pure thin film. It is further decreasing on the increase of PMMA mass ratio in the system which is the proof of aggregation-induced emission effect. The sample with the emitter:PMMA at mass ratio 9:1 exhibited the same emission properties as neat films but in addition was also optically clear those this system was used in LEEC. The LEEC cells with the simple structure ITO/PEDOT:PSS/Emitter:PMMA(9:1)/Al were prepared. The maximum brightness was 27 cd/m2 with the turn-on voltage of 8.7 V and CIE coordinates x=0.21 and y=0.29.