Ligand-assisted solid phase synthesis of mixed-halide perovskite nanocrystals for color-pure and efficient electroluminescence

Concealed fluorescent anti-counterfeiting paper prepared by loading perovskite and lead-metal-organic framework on cellulose fibers

Counterfeiting has caused great concern all over the world. What's more, the fluorescent materials play an important role in technological research and development for high-security. In this work, lead-metal-organic framework (Pb-MOF) and perovskite (MAPbBr3) were used in papers to achieving fluorescence counterfeiting. Pb-MOF, as the template or precursor of MAPbBr3, were in-situ generated on the surface of cellulose fibers (CFs) to preparing into hand sheets (Pb-MOF@CFs). Through the analysis of experimental results, it was found that ligands, reaction systems, addition sequences of drugs, time, etc. would affect the deposition of Pb-MOF on the surface of CFs. Using CH3NH3Br (MABr) as the anti-counterfeiting ink to write on Pb-MOF@CFs, the orange writing leaped across the paper, which caused by Pb in Pb-MOF chemically reacting with MABr forming MAPbBr3. The orange writing displayed green fluorescence under 365 nm ultraviolet lamp excitation. The orange writing with green fluorescence could be extinguished and reconstructed, which had promise for reuse. In addition, fluorescent security papers (MAPbBr3@Pb-MOFs@CFs) were prepared by immersing Pb-MOF@CFs in MABr solution. The fluorescence of MAPbBr3@Pb-MOFs@CFs opened when the surface of it was scraped under 365 nm ultraviolet lamp. This unique fluorescence property was very important in improving the security of products. Consequently, the ongoing research on perovskite and MOFs materials is of great significance.

Potential and perspectives of halide perovskites in light emitting devices

Light emitting diodes (LEDs) have become part of numerous electrical and electronic systems such as lighting, displays, status indicator lamps and wearable electronics. Owing to their excellent optoelectronic properties and deposition via simple solution process, metal halide perovskites possess unique potential for developing halide perovskite-based LEDs (PeLEDs) with superior photoluminescence efficiencies leading to external quantum efficiencies beyond 20% for PeLEDS. However, the limited durability, high operative voltages, and challenges of scale-up are persisting barriers in achieving required technology readiness levels. To build up the existing knowledge and raise the device performance this review provides a state-of-the-art study on the properties, film and device fabrication, efficiency, and stability of PeLEDs. In terms of commercialization, PeLEDs need to overcome materials and device challenges including stability, ion migration, phase segregation, and joule heating, which are discussed in this review. We hope, discussions about the strategies to overcome the stability issues and enhancement the materials intrinsic properties towards development more stable and efficient optoelectronic devices can pave the way for scalability and cost-effective production of PeLEDs.

Cesium Lead Bromide Perovskites: Synthesis, Stability, and Photoluminescence Quantum Yield Enhancement by Hexadecyltrimethylammonium Bromide Doping

Perovskite nanoparticles having a crystalline structure have attracted scientists' attention due to their great potential in optoelectronic and scintillation applications. The photoluminescence quantum yield (PLQY) is one of the main critical photophysical properties of the perovskite nanoparticles. Unfortunately, the main limitation of cesium lead halide perovskites is their instability in an ambient atmosphere, where they undergo a rapid chemical decomposition within time. For this purpose, hexadecyltrimethylammonium bromide (CTAB) was used as a surfactant dopant to test in the first place its effect on the stability of CsPbBr₃ perovskites and on the PLQY values of the prepared perovskites. The addition of CTAB has proven its efficiency in the formed CsPbBr₃ nanoparticles by increasing their thermal stability and by enhancing their PLQY up to 75%. These results were obtained after the successful preparation of CsPbBr₃ perovskite nanoparticles by optimizing three different reaction parameters, starting from the time of the reaction, moving to the concentration of lead bromide, and ending with the concentration of cesium oleate. Therefore, it was found that the most stable CsPbBr₃ perovskites were formed when mixing 0.15 g of lead bromide heated for 40 min with a volume of 1.2 mL of cesium oleate.

Stabilization of Lead-Reduced Metal Halide Perovskite Nanocrystals by High-Entropy Alloying

Colloidal metal halide perovskite (MHP) nanocrystals (NCs) are an emerging class of fluorescent quantum dots (QDs) for next-generation optoelectronics. A great hurdle hindering practical applications, however, is their high lead content, where most attempts addressing the challenge in the literature compromised the material's optical performance or colloidal stability. Here, we present a postsynthetic approach that stabilizes the lead-reduced MHP NCs through high-entropy alloying. Upon doping the NCs with multiple elements in considerably high concentrations, the resulting high-entropy perovskite (HEP) NCs remain to possess excellent colloidal stability and narrowband emission, with even higher photoluminescence (PL) quantum yields, η_PL, and shorter fluorescence lifetimes, τ_PL. The formation of multiple phases containing mixed interstitial and doping phases is suggested by X-ray crystallography. Importantly, the crystalline phases with higher degrees of lattice expansion and lattice contraction can be stabilized upon high-entropy alloying. We show that the lead content can be approximately reduced by up to 55% upon high-entropy alloying. The findings reported here make one big step closer to the commercialization of perovskite NCs.

Tough, stable and self-healing luminescent perovskite-polymer matrix applicable to all harsh aquatic environments

Gelatinous underwater invertebrates such as jellyfish have organs that are transparent, luminescent and self-healing, which allow the creatures to navigate, camouflage themselves and, indeed, survive in aquatic environments. Artificial luminescent materials that can mimic such functionality can be used to develop aquatic wearable/stretchable displays and water-resistant devices. Here, a luminescent composite that is simultaneously transparent, tough and can autonomously self-heal in both dry and wet conditions is reported. A tough, self-healable fluorine elastomer with dipole–dipole interactions is synthesized as the polymer matrix. It exhibits excellent compatibility with metal halide perovskite quantum dots. The composite possesses a toughness of 19 MJ m−3, maximum strain of 1300% and capability to autonomously self-heal underwater. Notably, the material can withstand extremely harsh aqueous conditions, such as highly salty, acidic (pH = 1) and basic (pH = 13) environment for more than several months with almost no decay in mechanical performance or optical properties.