Macroscopic Discolorization in Quantum Dot Color Converters for Microdisplay Applications

Quantum dot color converters (QDCCs) currently have the unsolved problems of photostability and discolorization in appearance after long-term operation in microdisplays. Instead of polymer-to-carbon conversion and/or impurity precipitation, the macroscopic bright-yellow-to-dark-brown discolorization is determined by microscopic interfacial chemical reactions of the QD-ligand-polymer system. The phenomenon has been confirmed to be related to multiple factors, including chemical transformation of the QD shell and partial degradation of the polymer, resulting in increased optical reflectance and reduced photoluminescence (PL) intensity in QDCCs. Our finding suggests that the photoexcitation of QDs in the polymer matrix should lead to detached surface ligands along with photocatalytic reactions, oxidizing the QD shell together with degrading the polymer chains.