Chemically resistant and thermally stable quantum dots prepared by shell encapsulation with cross-linkable block copolymer ligands

• Published in: NPG Asia materials 2020, Vol.12 (1), Article 19
• Main Authors: Ko, Jaewan, Jeong, Byeong Guk, Chang, Jun Hyuk, Joung, Joonyoung F., Yoon, Suk-Young, Lee, Doh C., Park, Sungnam, Huh, June, Yang, Heesun, Bae, Wan Ki, Jang, Se Gyu, Bang, Joona
• Format: Article
• Language: English
• Subjects: 639/301/357/1017; 639/638/455/957; Barriers; Biomaterials; Block copolymers; Chemistry and Materials Science; Crosslinking; Encapsulation; Energy Systems; Lewis acid; Ligands; Materials Science; Nanocomposites; Nanomaterials; Nanoparticles; Optical and Electronic Materials; Optoelectronics; Organic chemistry; Oxidation; Oxidizing agents; Photovoltaic cells; Polymethyl methacrylate; Quantum dots; Robustness; Shells (structural forms); Solar cells; Spectral emittance; Structural Materials; Surface and Interface Science; Surface defects; Thermal stability; Thin Films
• ISSN: 1884-4049; 1884-4057
• DOI: 10.1038/s41427-020-0200-4

Endowing quantum dots (QDs) with robustness and durability have been one of the most important issues in this field, since the major limitations of QDs in practical applications are their thermal and oxidative instabilities. In this work, we propose a facile and effective passivation method to enhance the photochemical stability of QDs using polymeric double shell structures from thiol-terminated poly(methyl methacrylate- b -glycidyl methacrylate) (P(MMA- b -GMA)-SH) block copolymer ligands. To generate a densely cross-linked network, the cross-linking reaction of GMA epoxides in the PGMA block was conducted using a Lewis acid catalyst under an ambient environment to avoid affecting the photophysical properties of the pristine QDs. This provides QDs encapsulated with robust double layers consisting of highly transparent PMMA outer-shell and oxidation-protective cross-linked inner shell. Consequently, the resulting QDs exhibited exceptional tolerance to heat and oxidants when dispersed in organic solvents or QD-nanocomposite films, as demonstrated under various harsh conditions with respect to temperature and oxidant species. The present approach not only provides simple yet effective chemical means to enhance the thermochemical stability of QDs, but also offers a promising platform for the hybridization of QDs with polymeric materials for developing robust light-emitting or light-harvesting devices. Nanomaterials: Protecting dots from defects A treatment that makes nanoparticles robust and thus more useful for optoelectronics has been developed by researchers in South Korea. Quantum dots are semiconductor particles just a few tens of nanometers in diameter. These tiny dimensions restrict the motion of electrons, which gives the dots properties similar to those of an atom. Specifically, they efficiently absorb and emit spectrally pure light, making them useful for displays, photodetectors and solar cells. However, quantum dots are sensitive to heat, moisture and oxidization. Joona Bang, Korea University, Seoul, and colleagues improved the thermochemical stability of quantum dots by surrounding them with a physical barrier to suppress the creation of surface defects. This protective shell was made using a cross-linkable polymer ligand and was shown to reduce the deleterious effects of exposure to high temperatures and an oxidizing agent. Quantum Dot: Shell cross-linking endows stability: Simple and facile cross-linking chemistry was employed to form the robu