Saturated and Multi‐Colored Electroluminescence from Quantum Dots Based Light Emitting Electrochemical Cells

Novel light emitting electrochemical cells (LECs) are fabricated using CdSe‐CdS (core‐shell) quantum dots (QDs) of tuned size and emission blended with polyvinylcarbazole (PVK) and the ionic liquid 1‐butyl‐3‐methylimidazolium hexafluorophosphate (BMIM‐PF₆). The performances of cells constructed using sequential device layers of indium tin oxide (ITO), poly(3,4‐ethylenedioxythiophene)‐poly(styrenesulfonate) (PEDOT:PSS), the QD/PVK/IL active layer, and Al are evaluated. Only color saturated electroluminescence from the QDs is observed, without any other emissions from the polymer host or the electrolyte. Blue, green, and red QD‐LECs are prepared. The maximum brightness (≈1000 cd m^‐2) and current efficiency (1.9 cd A^‐1) are comparable to polymer LECs and multilayer QD‐LEDs. White‐light QD‐LECs with Commission Internationale d'Eclairage (CIE) coordinates (0.33, 0.33) are prepared by tuning the mass ratio of R:G:B QDs in the active layer and voltage applied. Transparent QD‐LECs fabricated using transparent silver nanowire (AgNW) composites as the cathode yield an average transmittance greater than 88% over the visible range. Flexible devices are demonstrated by replacing the glass substrates with polyethylene terephthalate (PET).