Surface-Engineered Poly(ethylene oxide)-Grafted Quantum Dot Inks for Green-Solvent-Processed Electroluminescent Devices

Quantum dots (QDs) are promising emissive materials for next-generation optoelectronics, but conventional oleic acid (OA) capping necessitates toxic, nonpolar solvents such as toluene and chloroform, hindering environmentally sustainable solvent-based processing. Here, we report a green, solution-processable ligand-exchange strategy in which thiol-terminated poly(ethylene oxide) (PEO-SH) replaces OA on QDs, enabling stable dispersion in ethanol and water. By tuning the molecular weight of PEO, we identify PEO with Mn ≈ 2000 g/mol as an optimal ligand that provides a balanced combination of chain length and surface coverage, resulting in long-term colloidal stability and high photoluminescence quantum yield in polar media. Using these QD-PEO2k inks, we fabricate multilayer quantum dot light-emitting diodes (QLEDs) from ethanol and water/ethanol co-solvents, achieving a maximum external quantum efficiency of 2.12% and a current efficiency of 9.19 cd A-1. These results successfully serve as a proof-of-concept for generating functional electroluminescence from water/alcohol-based QD inks. Ultimately, this work establishes a foundational step toward reducing toxic solvent dependency and advancing sustainable manufacturing in solution-processed optoelectronics.