Search

Halide perovskite nanocrystals have easily tunable emissions throughout the visible spectrum, making them an extremely promising material for light‐emitting applications. Whereas high quantum yield and long‐term colloidal stability have already been achieved for nanocrystals emitting in the red and green spectral range, the blue region currently lags behind with low quantum yields and insufficient colloidal stability. In this study, we present a facile synthetic and postsynthetic approach for obtaining two‐dimensional CsPbBr3 nanoplatelets (NPLs) with homogeneous‐thickness control of their solidified surface, resulting in sharp photoluminescence and electroluminescence peaks with a deep‐blue emission at 465‐nm wavelength owing to quantum confinement. The subsequent addition of a solidifying ligand solution seals the surface defects likely stemming from vacancies within a subensemble of weakly emissive NPLs. The overall photoluminescence quantum yield of the blue‐emissive colloidal dispersions is consequently enhanced by 65% ± 2%. [ABSTRACT FROM AUTHOR]

Although metal halide perovskites are candidate high‐performance light‐emitting diode (LED) materials, blue perovskite LEDs are problematic: mixed‐halide materials are susceptible to phase segregation and bromide‐based perovskite quantum dots (QDs) have low stability. Herein, a novel strategy for highly efficient, stable cesium lead bromide (CsPbBr3) QDs via in situ surface reconstruction of CsPbBr3–Cs4PbBr6 nanocrystals (NCs) is reported. By controlling precursor reactivity, the ratio of CsPbBr3 to Cs4PbBr6 NCs is successfully modulated. A high photoluminescence quantum yield (PLQY) of >90% at 470 nm is obtained because octahedron CsPbBr3 QD surface defects are removed by the Cs4PbBr6 NCs. The defect‐engineered QDs exhibit high colloidal stability, retaining >90% of their initial PLQY after >120 days of ambient storage. Furthermore, thermal stability is demonstrated by a lack of heat‐induced aggregation at 120 °C. Blue LEDs fabricated from CsPbBr3 QDs with reconstructed surfaces exhibit a maximum external quantum efficiency of 4.65% at 480 nm and excellent spectral stability. [ABSTRACT FROM AUTHOR]

Surface engineered iron oxide nanoparticles (IONPs) with catecholic ligands have been investigated as alternative T 1 contrast agents. However, complex oxidative chemistry of catechol during IONP ligand exchange causes surface etching, heterogeneous hydrodynamic size distribution, and low colloidal stability because of Fe 3+ mediated ligand oxidation. Herein, we report highly stable and compact (∼10 nm) Fe 3+ rich ultrasmall IONPs functionalized with a multidentate catechol-based polyethylene glycol polymer ligand through amine-assisted catecholic nanocoating. The IONPs exhibit excellent stability over a broad range of pHs and low nonspecific binding in vitro . We also demonstrate that the resultant NPs have a long circulation time (∼80 min), enabling high resolution T 1 magnetic resonance angiography in vivo . These results suggest that the amine assisted catechol-based nanocoating opens a new potential of metal oxide NPs to take a step forward in exquisite bio-application fields., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)

Organic optoelectronic devices that can be fabricated at low cost have attracted considerable attention because they can absorb light over a wide frequency range and have high conversion efficiency, as well as being lightweight and flexible. Moreover, their performance can be significantly affected by the choice of the charge-selective interlayer material. Nonstoichiometric nickel oxide (NiO x ) is an excellent material for the hole-transporting layer (HTL) of organic optoelectronic devices because of the good alignment of its valence band position with the highest occupied molecular orbital level of many p-type polymers. Herein, we report a simple low-temperature process for the synthesis of NiO x nanoparticles (NPs) that can be well dispersed in solution for long-term storage and easily used to form thin NiO x NP layers. NiO x NP-based organic photodiode (OPD) devices demonstrated high specific detectivity ( D *) values of 10 12 -10 13 jones under various light intensities and negative biases. The D * value of the NiO x NP-based OPD device was 4 times higher than that of a conventional poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)-based device, an enhancement that originated mainly from the 16 times decreased leakage current. The NiO x NP-based OPD device demonstrated better reliability over a wide range of light intensities and operational biases in comparison to a device with a conventional sol-gel-processed NiO x film. More importantly, the NiO x NP-based OPD showed long-term device stability superior to those of the PEDOT:PSS and sol-gel-processed NiO x -based devices. We highlight that our low-temperature solution-processable NiO x NP-based HTL could become a crucial component in the fabrication of stable high-performance OPDs.

Although metal halide perovskites are candidate high-performance light-emitting diode (LED) materials, blue perovskite LEDs are problematic: mixed-halide materials are susceptible to phase segregation and bromide-based perovskite quantum dots (QDs) have low stability. Herein, a novel strategy for highly efficient, stable cesium lead bromide (CsPbBr 3 ) QDs via in situ surface reconstruction of CsPbBr 3 -Cs 4 PbBr 6 nanocrystals (NCs) is reported. By controlling precursor reactivity, the ratio of CsPbBr 3 to Cs 4 PbBr 6 NCs is successfully modulated. A high photoluminescence quantum yield (PLQY) of >90% at 470 nm is obtained because octahedron CsPbBr 3 QD surface defects are removed by the Cs 4 PbBr 6 NCs. The defect-engineered QDs exhibit high colloidal stability, retaining >90% of their initial PLQY after >120 days of ambient storage. Furthermore, thermal stability is demonstrated by a lack of heat-induced aggregation at 120 °C. Blue LEDs fabricated from CsPbBr 3 QDs with reconstructed surfaces exhibit a maximum external quantum efficiency of 4.65% at 480 nm and excellent spectral stability., (© 2021 The Authors. Advanced Science published by Wiley-VCH GmbH.)

Recently, the double perovskite Cs 2 AgInCl 6 , which has high stability and low toxicity, has been proposed as a potential alternative to Pb-based perovskites. However, the calculated parity-allowed transition bandgap of Cs 2 AgInCl 6 is 4.25 eV; this wide bandgap makes it difficult to use as an efficient solar absorber. In this study, we explored the effect of Cu doping on the optical properties of Cs 2 AgInCl 6 double perovskite nano- and microcrystals (MCs), particularly in its changes of absorption profile from the ultraviolet (UV) to near-infrared (NIR) region. Undoped Cs 2 AgInCl 6 showed the expected wide bandgap absorbance, but the Cu-doped sample showed a new sharp absorption peak at 419 nm and broad absorption bands near 930 nm, indicating bandgap reduction. Electron paramagnetic resonance (EPR) spectroscopy demonstrated that this bandgap reduction effect was due to the Cu doping in the double perovskite and confirmed that the Cu 2+ paramagnetic centers were located on the surface of the nanocrystals (NCs) and at the center of the perovskite octahedrons (g ∥ > g ⊥ > g e ). Finally, we synthesized Cu-doped Cs 2 AgInCl 6 MCs and observed results similar to those of the NCs, showing that the application range could be expanded to multidimensions., Competing Interests: The authors declare no competing financial interest., (© 2021 The Authors. Published by American Chemical Society.)