Heat- and water-proof film of quantum dot/siloxane composites

Ultrastable quantum dot/siloxane composite films have been developed by encapsulation of quantum dots in a siloxane host matrix, whose photoluminescence (PL) quantum yield (QY) exhibits no degradation under hot or humid environments for 40 days.

Article  |  Spring 2017

A recent surge of interest in “quantum dots” is derived from commercialized TV products based on these exciting materials. Quantum dots (QDs), semiconductor nanocrystals within a strong quantum confinement regime, exhibit narrow emission bandwidth and high emission quantum yield (QY) and have thus been considered an ideal fluorophore for high color-resolution display devices.

The large surface-to-volume ratio and relatively weak binding of surface ligands make QDs susceptible to oxidation, which had hampered the integration of these otherwise impeccable materials into commercial products. In fact, the recent commercialization was possible because barrier films protect QD/polymer film from oxygen and water. One obvious problem is that the barrier films are relatively expensive; therefore, the commercially available QD-based products can lose their edge in cost.

In a study led by Prof. Byeong-Soo Bae in the Department of Materials Science and Engineering at Korea Advanced Institute of Science and Technology (KAIST) and Prof. Doh C. Lee in the Department of Chemical and Biomolecular Engineering at KAIST, QD/polymer film that exhibits little to no degradation under heat or moisture has been developed. Siloxane encapsulation is a key to ultrastable film: bonding forms between the ligands on the QD surface and heat-resistive siloxane via a free radical addition reaction and sol-gel condensation reaction. Unlike previously available approaches, the QD/siloxane composite is based on chemical and robust bonding between QDs and resin, making the QDs disperse evenly in the matrix and keeping the siloxane passivation layer intact on the surface after QDs are exposed to harsh conditions. In fact, QD/siloxane composite films turn out to maintain their QY under various harsh oxidative conditions: 85°C/5% relative humidity (RH), 85°C/85% RH, strongly acidic, and strongly basic environments for 40 days. The QD/siloxane composite film appears to remain equally emissive even after being immersed into boiling water (100°C). Interestingly, the PL QY of the QD/siloxane composite film is noticeably enhanced when the film is exposed to a moist environment by adsorbing water molecules, which opens a new, facile avenue to curing dimmed QD-containing films. An article on this research entitled “Quantum Dot/Siloxane Composite Film Exceptionally Stable against Oxidation under Heat and Moisture” was published in November 2016 in the Journal of the American Chemical Society.

Hwea Yoon Kim, the graduate student in the Department of Materials Science and Engineering at KAIST in charge of the experiments explained, “Given its excellent stability, the siloxane-encapsulation method will push the envelope of QD composite films as an organic/inorganic hybrid system in display applications. I am aware that a lot of companies want to get rid of the need for barrier films, and I am happy that we have provided one solution that can resonate in the display industry.”

Reference: H. Y. Kim, D.-E. Yoon, J. Jang, D. Lee, G.-M. Choi, J. H. Chang, J. Y. Lee, D. C. Lee*, B.-S. Bae*, Journal of the American Chemical Society, 138, 16478-16485 (2016).

Additional link for more information:
http://pubs.acs.org/doi/abs/10.1021/jacs.6b10681 (Article)
http://www.sol-gel.net/ (Prof. Byeong-Soo Bae)
http://dclee.kaist.ac.kr/ (Prof. Doh C. Lee)

 polymer composite film (gray) monitored over 40 days of aging.