The challenges afflicting cesium lead halide perovskite nanocrystals (PNCs) are long-term stability and deterioration of photoluminescence (PL) properties with time, hindering its commercialization applicability. The presence of surface defects on cesium lead bromide (CsPbBr 3 ) PNCs commonly lead to the degradation of PL properties via ligand loss. In this work, we explored benzoic acid post-treatment to improve the PL and long-term stability of green-emitting CsPbBr 3 PNCs. The surface defects are passivated via co-ordination of carboxyl group with under coordinated surface lead atoms. The photoluminescence quantum yield is in unity with benzoic acid (BA) post-treatment, also reflected in PL decay profiles. The BA-CsPbBr 3 PNCs exhibit excellent stability for more than a year. Thirty-six percent of the initial PL intensity is preserved for BA-CsPbBr 3 PNCs, while the PL is completely quenched for untreated CsPbBr 3 PNCs within 24 h of continuous UV illumination (λ ex = 365 nm). Nearly 21% of the PL is preserved for BA-CsPbBr 3 PNCs, whereas the PL is quenched instantly for untreated PNCs with ethanol treatment. The green emission from the fabricated down-conversion LED device plotted in CIE 1931 demonstrated high color purity.
Colloidal cesium lead halide (CsPbX3) perovskite nanocrystals (PNCs) have been shown to exhibit very bright tunable photoluminescence (PL) in the entire visible range and narrow emission widths with composition control. However, challenges afflict the stability of PNCs, which limits their usage in practical applications. Surface passivation with an additional ligand could be an excellent, easy, and facile approach to enhance the photoluminescence and stability of PNCs. To address the issue of stability, we introduce the abundantly available ascorbic acid as a surface capping ligand to achieve high photoluminescence and stability of CsPbX3 PNCs via post-treatment. Ascorbic acid helps in improving the photoluminescence (PL) quantum yield of all halide variant PNCs, particularly CsPbBr3 and CsPb(Br/I)3 PNCs. With ascorbic acid post-treatment, the luminescence decay profiles are improved with a significant increase in the PL lifetime. As a proof-of-concept, we recorded PL data of untreated and ascorbic acid-treated PNCs for a considerable amount of time and found that ascorbic acid-capped PNCs exhibit exceptional ambient stability, photostability, and thermal stability. The pure CsPbI3 PNCs, which are thermodynamically unstable at room temperature, become ultrastable in the presence of ascorbic acid, where they showed the preservation of the luminescent phase for 55 d since the date of synthesis when stored in open atmospheric conditions. The ascorbic acid-treated CsPb(Br/I)3 PNCs also exhibited excellent stability with no trace of halide segregation, unlike the as-synthesized mixed halide perovskites, wherein a blue shift of PL is observed with a significant loss in emission. Stabilizing CsPbX3 PNCs of different halide compositions via a simple surface treatment with ascorbic acid could form the basis for futuristic light-emitting applications.
Cesium−lead halide (CsPbX 3 ) perovskite nanocrystals (PNCs) have attracted significant attention from researchers because of their essential optoelectronic properties, especially long charge-carrier transfer, high efficiency in visible-light absorption, long excited-state lifetimes, etc. Because of these properties, these materials exhibit outstanding charge transfer and charge separation, which allows them to be used for solar cell applications. Recently, CsPbX 3 perovskites have emerged as photocatalysts. In photovoltaics or photocatalysis, upon photoexcitation, the exciton dissociates, and the electron/ hole is transmitted from the conduction/valence bands to the electron/hole acceptors. Therefore, it is essential to understand how charge transfer occurs at the PNC interface, which can help a researcher maximize the output in solar cells and photocatalytic efficiency. Specifically, we emphasize using PNCs as electron and hole donors in this review. We have outlined different chargetransfer dynamics based on critical factors and discussed their optoelectronic properties. Electron/hole-transfer dynamics are the most concerning characteristic; thus, we reviewed the relevant literature that reported efficient electron/hole-transfer performance. In the end, we highlighted recent developments in the use of PNCs as photocatalysts in organic synthesis.
Colloidally synthesized cesium lead halide (CsPbX3; X = Cl, Br, and I) perovskite nanocrystals (PNCs) often suffer from poor ambient and environmental stability conditions, limiting their practical applications. The commonly used surfactant oleylamine is converted to the oleylammonium cation, which pulls out the halide anion from the PNC surface, thus disrupting the structural integrity and stability of the nanocrystal. We developed a simple, completely amine-free colloidal synthesis with a hot injection method under open-atmospheric conditions and introduced bromooctane as a bromine precursor to overcome the above issues. These as-synthesized amine-free PNCs show a photoluminescence quantum yield (PLQY) of around 60%, and the size of PNCs is ∼25 nm. Moreover, these amine-free PNCs were highly stable in colloidal solutions and thin films for more than 5 months under ambient conditions, with 66% of their initial PLQY. In addition, these PNCs show exceptional stability under different environmental conditions, with 44% of the initial PL even after water treatment under 6 h and 28% of the initial PL under ethanol treatment of 120 min. Furthermore, they exhibit excellent photostability for 96 h and retain 36% of their initial PL under ceaseless UV light irradiation at 365 nm (8 W/cm2). In addition, these PNCs have good stability upon heat treatment and maintain 34% of the initial PL upon heating up to 90 °C. Finally, we fabricated a green-emitting down-conversion light-emitting diode (LED) using these amine-free PNCs. Therefore, we envision that these amine-free CsPbBr3 PNCs are perhaps ideal candidates for perovskite-based display applications.
In recent years, colloidal cesium lead halide (CsPbX3) perovskite nanocrystals (PNCs) have attracted significant attention from researchers due to their unique optical properties and potential use in optoelectronic applications. In colloidal synthesis, oleic acid and oleylamine are commonly used as surface-capping ligands. Although oleylamine plays a crucial role in maintaining the colloidal stability and surface passivation of PNCs, its dynamic equilibrium with oleic acid leads to the formation of labile oleylammonium, which pulls halides from the surface of PNCs and thus degrades the crystals. In this Perspective, we summarize the various approaches for eliminating the amines to make high-quality, photostable, and amine-free CsPbX3 PNCs. In addition, we look over the prospects of these PNCs regarding stability in different environmental conditions, photoluminescence properties, and optoelectronic device performance. This perspective will give a broad overview of amine-free PNCs starting from their synthesis, challenges, and optoelectronic properties to their future prospects.
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