ABSTRACT
Metal halide perovskites offer ample opportunities to develop advanced optoelectronic devices. This work showcases that the integration of metal halide perovskites into metal oxide nanoshells with controllable interior cavities can enable water-vapor-responsive dual-mode switching of fluorescence and structural color. Through a ship-in-a-bottle method to introduce a controlled amount of CsPbBr3 into MnO2 nanoshells, we have designed CsPbBr3@MnO2 yolk-shell nanostructures, which can uptake a defined amount of water to exhibit rapid (less than 1 s) and reversible (≥100 cycles) responses in both fluorescence on-off and color change when exposed to dynamic water vapor. These responses originate from the water-triggered phase transformation of CsPbBr3 to CsPb2Br5 and the structural color change of the MnO2 shell. The altered electronic and bonding structure at the oxide-halide interface, rapid water accumulation in the yolk-shell cavity, and protective effect of the oxide shell facilitate the reversible transformations. The response characteristics of the yolk-shell nanostructures have been further demonstrated in fabricating patterned films capable of multiple fluorescence/structural color responses, highlighting their potential for applications in advanced anticounterfeiting and encryption.
ABSTRACT
Daytime radiative cooling with high solar reflection and mid-infrared emission offers a sustainable way for cooling without energy consumption. However, so far sub-ambient daytime radiative coolers typically possess white/silver color with limited aesthetics and applications. Although various colored radiative cooling designs have been pursued previously, multi-colored daytime radiative cooling to a temperature below ambient has not been realized as the solar thermal effect in the visible range lead to significant thermal load. Here, we demonstrate that photoluminescence (PL) based colored radiative coolers (PCRCs) with high internal quantum efficiency enable sub-ambient full-color cooling. As an example of experimental demonstration, we develop a scalable electrostatic-spinning/inkjet printing approach to realize the sub-ambient multi-colored radiative coolers based on quantum-dot photoluminescence. The unique features of obtained PCRCs are that the quantum dots atop convert the ultraviolet-visible sunlight into emitted light to minimize the solar-heat generation, and cellulose acetate based nanofibers as the underlayer that strongly reflect sunlight and radiate thermal load. As a result, the green, yellow and red colors of PCRCs achieve temperatures of 5.4-2.2 °C below ambient under sunlight (peak solar irradiance >740 W m-2), respectively. With the excellent cooling performance and scalable process, our designed PCRC opens a promising pathway towards colorful applications and scenarios of radiative cooling.
ABSTRACT
Cs4PbBr6 nanocrystals (NCs) have been recently studied as they can enhance the light emitting efficiency and stability of CsPbBr3 NCs. However, the synthesis of Cs4PbBr6 NCs is often accompanied by the generation of CsPbBr3 NCs, and less attention has been paid to how to exactly control their formation. Here, we investigated the key factors in deciding the final products in the hot-injection synthesis by a modified amine-free method. We found that the molarity ratio of Cs/Pb dominated the final products, while the amount of bromine had a relatively small effect. In addition, introducing a certain amount of oleylamine into the amine-free reaction leads to the formation of Cs4PbBr6, instead of CsPbBr3 NCs. This clearly shows that the protection ligand oleylamine also plays an important role in the formation of Cs4PbBr6 NCs. This well understood and fine control of the synthesis may inspire a new CsPbBr3@Cs4PbBr6 core-shell structure, with the same chemical elements but a different crystal phase in the core and the shell. This nanostructure would open a new avenue for enhancing the stability of perovskite nanocrystals.
ABSTRACT
All-inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are highly attractive due to their outstanding optical and electrical properties. However, poor stability and easy anion exchanges between CsPbX3 nanocrystals with different halides limit their applications in light-emitting diodes (LEDs). To solve the problems, we developed an approach to in situ synthesize CsPbX3 NCs into porous silica colloidal spheres, which can effectively prevent anion exchange and increase photo stability. Based on our results, we first proved that the anion exchange between CsPbX3 nanocrystals is mainly driven by physical collision of the nanocrystals, not requiring a bridge such as a solvent. We subsequently used an optimized ratio of green, red, and blue SiO2/CsPbX3 composites as solid-state luminescent materials to fabricate single-layer white light-emitting diodes (WLEDs). No anion exchanges have been observed in the LED fabrication and lighting process.
