Highly stable siloxane-encapsulated perovskite nanocrystal hybrid composite for color-converting layer in display

Abstract

Organic-inorganic hybrid perovskites nanocrystals (PNCs), with ABX$_3$ structure (A: organic cation, B: metal cation, X: halide anion), are promising color-converting material due to their superior optical properties that meets the high luminescence efficiency and high color standard of Rec. 2020, compared to inorganic quantum dots. However, the external environments such as moisture, heat, and light can easily cause the degradation of PNCs because of their intrinsic instability with ionic nature and thus leads to loss of optical properties. To solve these problems, synthesizing PNC/polymer composite is an effective method to prevent permeation of oxygen and moisture to surface of PNCs. Recently, my group reported siloxane-encapsulated PNC composite which exhibited high stability. However, the composite encounter limited stability in high temperature and high blue light irradiation. To guarantee stability in high temperature condition, the passivation of PNCs by surface ligands with robustness and functionality is also necessary. Therefore, stable PNCs with robust ligand that chemically interacts with the polymer matrix should be developed. In this thesis, PNC stability was significantly enhanced by chemical encapsulation for color converter. Initially, I synthesized M-PNC (Methacrylate-functionalized PNC) with robust siloxane ligand to give compatibility and functionality for cross-linking to siloxane matrix. Then, M-PNC was encapsulated in siloxane matrix via in-situ sol-gel reaction, where the PNCs were chemically dispersed in matrix at the initial stage of resin synthesis. Subsequently, to form solidified composite film (M-PNC/siloxane film), UV-curing process was followed. As a result, M-PNC/siloxane film showed long-term stability in various harsh environments (ambient air, water, 85 ℃ / 85% relative humidity, polar solvents, and blue light irradiation) without additional protecting layer (inorganic shell or barrier film). Wide color gamut white LED (125% of NTSC 1931, 93% of Rec. 2020) was demonstrated by introducing red-emitting inorganic phosphor KSF (K$_2$SiF$_6$:Mn$^{4+}$), which out performs conventional inorganic quantum dots. Finally, the M-PNC-based color-converting layer was fabricated to show potential towards high-resolution display.