Sol-Gel Synthesized Siloxane Encapsulated Quantum Dot Resin with Excellent Dispersion and Stability

Abstract

Semiconducting nanocrystals, also known as quantum dots (QDs), have great potential to apply wavelength converting materials for next-generation display applications due to their unique optical properties such as narrow emission spectra, color tenability depending on size, wide color garmut, and high photoluminescence quantum yield (PLQY). However, QDs have various limitations for practical applications because of weakness to oxygen and moisture, which can cause degradation of their luminescence. Mostly, QDs are mixed with polymer resins to coat on the film or dispense on the LED packaging. Thus, uniformly dispersed QD in matrix resin should be prepared and its cured product of coating or bulk films should have thermal and moisture stability to be practically applied. However, currently used QD/polymer resin is hard to be uniformly dispersed due to low compatibility between QDs and polymer resin. Also, its cured products are vulnerable to heat and moisture since polymer has low thermal stability and QDs are easily attacked by oxygen and water in the polymer matrix. Recently, we reported new siloxane encapsulated QD (core: CdSe / shell: CdZnS / ligand: oleic acid, from Ecoflux) (SE-QD) resin through in-situ sol-gel condensation reaction of 3-methacryloxypropyltrimethoxysilane (MPTS) and diphenylsilanediol (DPSD) in the existence of QDs. [1] The photo-cured SE-QD resin containing methacrylate groups shows almost permanent dispersion stability of QD in siloxane matrix and its cured films show long-term stability in harsh environment (85 oC in air and 85 oC & 85 %RH). However, photo-curing of SE-QD resin is not desirable for practical application. Because it is difficult for completely curing of the resin due to UV light absorption of QDs and their photo-oxidation degradation. Also, thermal stability is limited due low degradation temperature of methacrylate. Herein, we fabricate new siloxane encapsulated QD (TSE-QD) resin which is thermally cured (especially hydrosilylation curing). The siloxane matrix for TSE-QD was already confirmed to show higher thermal stability over 180 oC and better optical transparency to be used as the LED encapsulant. [2] The fabricated TSE-QD resin is successfully cured by hydrosilylation reaction with no degradation of QD even during high temperature sol-gel reaction and thermal curing process. Especially, the cured films of TSE-QD resin represent better thermal stability (at 120 oC in ambient condition) compared to our previous photo-cured SE-QD. It is also stable at high temperature & high humidity condition (85 oC & 85 %RH) and better photo-stability. Therefore, the siloxane encapsulated QD resin has great potential for QD based display applications.