Cesium halide lead (CsPbX 3 ) perovskite nanocrystals (NCs) have been extensively studied in recent years for their unique capability of postsynthesis anion exchange, providing facile tunability of band gaps and optical properties. In this work, we demonstrate for the first time a simple approach to the tunable anion exchange of CsPbX 3 perovskite NCs via radiation chemistry of inert halohydrocarbons. The anion exchange extents are monitored by shifting of fluorescence emission peaks and ultraviolet−visible absorbance edges and are precisely controlled by tuning the absorbed doses and the adjustable addition of halohydrocarbons. At the same absorbed doses, the anion exchange extents by halohydrocarbons are dependent on the linear attenuation coefficients of halohydrocarbons. Radiation-induced anion exchange can passivate defects in CsPbX 3 NCs, resulting in the fluorescence enhancement. The morphology of perovskite NCs almost remains intact after radiation-induced anion exchange.
It is still challenging to achieve both good stability and high PLQYs for perovskite NCs because of their ionic nature and structural defects. In this work, tungstosilicic acid (TSA) is used for the surface passivation of cesium lead halide perovskite NCs. Near-unity PLQY is achieved for CsPbBr3 NCs after surface passivation with a suitable amount of TSA. XRD in conjunction with XPS analysis shows that TSA binds hydrophobic chains of OAm onto the surface of CsPbBr3 NCs. XPS results also demonstrate that TSA passivation can change the charge distribution of the cations on the surface layers, which can enhance the interaction with surface traps. PL decay analysis reveals that trap states arising from the surface defects are significantly decreased after TSA passivation. TSA-passivated CsPbBr3 NCs demonstrate long-term ambient stability and good resistances to polar solvents and maintain about 80% of their initial PL intensity after storage under ambient conditions for 50 days. It is further found that TSA passivation is able to improve the PLQYs of a broad spectrum of CsPbX3 (X = Cl, Br, I) NCs without hindering the tunability of the band gaps and PL colors of CsPbX3 NCs via anion exchange.
Surfactant ligands are important in the synthesis of inorganic perovskite nanocrystals (NCs), not only for stabilizing NCs but also for surface defect passivation. A new polymerizable surfactant ligand with a multidentate L-cysteine head, a long oleoyl tail, and a polymerizable styrenyl group (NOSVC) is designed for the postsynthesis treatment and stabilization of colloidal CsPbBr 3 NCs in this work. 1 H nuclear magnetic resonance and X-ray photoelectron spectroscopy analysis show that the L-cysteine head has strong interactions with the NCs. The absolute photoluminescence quantum yields of the colloidal NCs are increased from 45.1% of the pristine NCs stabilized with oleic acid/oleyl amine to 91.8% after NOSVC treatment. NOSVC-stabilized CsPbBr 3 colloidal NCs show enhanced stabilities when exposed in polar solvents. The NOSVCstabilized CsPbBr 3 NCs in a solid film state allow for a photopolymerization to be carried out with the assistance of a photoinitiator. The polymerized films of NOSVC-treated NCs exhibit significantly enhanced stability against thermal radiation, ultraviolet irradiation, and humidity. We also fabricated self-healing polymer films incorporating NOSVC-treated CsPbBr 3 NCs as a green filter for a white light-emitting diode device. The green light-emitting films are very stable in humid environments, revealing the great application potential of NOSVC-treated CsPbBr 3 NCs in flexible display and lighting devices.
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