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.

Mastery over the shape of a colloidal nanocrystal has proven to be a powerful tool to control its properties and broaden the range of applications. This is particularly relevant in the case of branched semiconductor nanocrystals, which are of special interest due to their unique optoelectronic properties. An archetypal example of a branched shape in nanocrystals is represented by particles made of a core from which four arms/pods are grown, so-called tetrapods. Many research groups have investigated these structures, driven by their potential use in optics, in which their geometry helps to efficiently capture photons from a wide range of incident angles. In addition, tetrapods have increasingly attracted much attention because of their ability to self-assemble into, for instance, percolating networks, providing an efficient way to create electronic pathways in devices that rely upon charge transport. This has stimulated in part the development of synthetic protocols to control the growth of uniform arms in particles of different sizes and, thus, to tune their functionalities, expanding the configurations that can be built via self-assembly. Recently, researchers have designed several innovative approaches for the synthesis of tetrapods, which include the combination of different material components in the same particle to achieve multiple properties. In this review, we will focus on metal chalcogenide semiconductor tetrapod-shaped nanocrystals and summarize recent progress on their synthesis methods, highlighting the various routes that aim to fabricate hybrid tetrapod nanostructures. We will examine the fundamental optoelectronic properties of tetrapod-shaped nanocrystals and provide an up-to-date overview of the strategies developed for their self-organization into different architectures. Finally, we will review their applications in photovoltaics, optoelectronics, and mechanical devices.

Recently lead halide perovskite nanocrystals (PNCs) have attracted intense interest as promising active materials for optoelectronic devices. However, their extensive applications are still hampered by poor stability in ambient conditions....

Anion-exchange with metal chloride salts in CsPbBr3 perovskite nanocrystals.

Cesium lead halide perovskite nanocrystals (NCs) CsPbX3 (X=Cl, Br, and I) have been prominent materials in the last few years due to their high photoluminescence quantum yield (PLQY) for light‐emitting diodes and other significant applications in photovoltaics and optoelectronics. In colloidal CsPbX3 synthesis, the most commonly used ligands are oleic acid and oleylamine. The latter plays an important role in surface passivation but may also be responsible for poor colloidal stability as a result of facile proton exchange leading to the formation of labile oleylammonium halide, which pulls halide ions out of the NC surface. Herein, a facile, efficient, completely amine‐free synthesis of cesium lead bromide perovskite nanocrystals using hydrobromic acid as halide source and tri‐n‐octylphosphane as ligand under open‐atmospheric conditions is demonstrated. Hydrobromic acid serves as labile source of bromide ion, and thus this three‐precursor approach (separate precursors for Cs, Pb, Br) gives more control than a conventional single‐source precursor for Pb and Br (PbBr2). The use of HBr paved the way to eliminate oleylamine, and thus the formation of labile oleylammonium halide can be completely excluded. Various Cs:Pb:Br molar ratios were studied and optimum conditions for making very stable CsPbBr3 NCs with high PLQY were found. These completely amine‐free CsPbBr3 perovskite NCs synthesized under bromine‐rich conditions exhibit good stability and durability for more than three months in the form of colloidal solutions and films, respectively. Furthermore, stable tunable emission across a wide spectral range through anion exchange was demonstrated. More importantly, this work reports open‐atmosphere‐stable CsPbBr3 NCs films exhibiting strong PL, which can be further used for optoelectronic device applications.