Hydrophilic Conjugated Polymers for Sustainable Fabrication of Deep‐Red Light‐Emitting Electrochemical Cells

Abstract

It is crucial to develop functional electronic materials that can be processed from green solvents to achieve environmentally sustainable and cost‐efficient printing fabrication of organic electronic devices. Here, the design and cost‐efficient synthesis of two hydrophilic and emissive conjugated polymers, TQ‐OEG and TQ2F‐OEG, are presented, which are rendered hydrophilic through the grafting of oligo(ethylene glycol) (OEG) solubilizing groups onto the thiophene‐quinoxaline conjugated backbone and thereby can be processed from a water:ethanol solvent mixture. It is shown that the introduction of the OEG groups enables for a direct dissolution of salts by the neat polymer for the attainment of solid‐state ion mobility. These properties are utilized for the design and development of light‐emitting electrochemical cells (LECs), the active materials of which can be solution cast from a water:ethanol‐based ink. It is specifically shown that such an LEC device, comprising an optimized blend of the TQ2F‐OEG emitter and a Li salt as the active material positioned between two air‐stabile electrodes, delivers deep‐red emission (peak wavelength = 670 nm) with a radiance of 185 µW m⁻² at a low drive voltage of 2.3 V. This study contributes relevant information as to how polymers and LEC devices can be designed and fabricated to combine functionality with sustainability.