Fabrication of Cross-Linked Quantum Dot/Colorless-Polyimide Nanocomposites for Highly Efficient and Long-Term Stable Light-Emitting Diodes

Quantum dot (QD)/colorless-polyimide (CPI) nanocomposites were fabricated and utilized as the color conversion layer in a light-emitting diode. CPIs with different lengths and end groups were synthesized and used both as surface ligands on the QDs and matrix polymers. Thereafter, nanocomposites were fabricated by the cross-linking reaction between the diphthalic anhydride-terminated matrix CPI and diamine-terminated CPI that was grafted onto the QDs. The degree of cross-linking in the nanocomposites was controlled by varying the length of the matrix CPI and QD concentrations; the highest quantum efficiency was observed at the highest degree of cross-linking because of the improved dispersion of the QDs. The cross-linked QD/CPI nanocomposite exhibited superior fluorescent properties and stability against heat and moisture to the un-cross-linked QD/CPI and QD/poly(methyl methacrylate) nanocomposites. Light-emitting diodes with high color accuracy and a wide color gamut were successfully fabricated using the cross-linked QD/CPI nanocomposite.