Stabilization of CsPbBr3 Nanowires Through SU-8 Encapsulation for the Fabrication of Bilayer Microswimmers with Magnetic and Fluorescence Properties

All-inorganic cesium lead halide (CsPbX3, X = Cl, Br, I) perovskite nanocrystals have drawn great interest because of their excellent photophysical properties and potential applications. However, their poor stability in water greatly limited their use in applications that require stable structures. In this work, a facile approach to stabilize CsPbBr3 nanowires is developed by using SU-8 as a protection medium; thereby creating stable CsPbBr3/SU-8 microstructures. Through photolithography and layer-by-layer deposition, CsPbBr3/SU-8 is used to fabricate bilayer achiral microswimmers (BAMs), which consist of a top CsPbBr3/SU-8 layer and a bottom Fe3O4 magnetic layer. Compared to pure CsPbBr3 nanowires, the CsPbBr3/SU-8 shows long-term structural and fluorescence stability in water against ultrasonication treatment. Due to the magnetic layer, the motion of the microswimmers can be controlled precisely under a rotating magnetic field, allowing them to swim at low Reynolds number and tumble or roll on surfaces. Furthermore, CsPbBr3/SU-8 can be used to fabricate various types of planar microstructures with high throughput, high consistency, and fluorescence properties. This work provides a method for the stabilization of CsPbBr3 and demonstrates the potential to mass fabricate planar microstructures with various shapes, which can be used in different applications such as microrobotics.

Stability Enhancement in All-Inorganic Perovskite Light Emitting Diodes via Dual Encapsulation

Addressing the challenge of lighting stability in perovskite white light emitting diodes (WLEDs) is crucial for their commercial viability. CsPbX3 (X = Cl, Br, I, or mixed) nanocrystals (NCs) are promising for next-generation lighting due to their superior optical and electronic properties. However, the inherent soft material structure of CsPbX3 NCs is particularly susceptible to the elevated temperatures associated with prolonged WLED operation. Additionally, these NCs face stability challenges in high humidity environments, leading to reduced lighting performance. This study introduces a two-step dual encapsulation method, resulting in CsPbBr3@SiO2/Al2SiO5 composite fibers (CFs) with enhanced optical stability under extreme conditions. In testing, WLEDs incorporating these CFs, even under prolonged operation at high power (100 mA for 9 h), maintain consistent electroluminescence (EL) intensity and optoelectronic parameters, with surface temperatures reaching 84.2 °C. Crucially, when subjected to 85 °C and 85% relative humidity for 200 h, the WLEDs preserve 97% of their initial fluorescence efficiency. These findings underscore the efficacy of the dual encapsulation strategy in significantly improving perovskite material stability, marking a significant step toward their commercial application in optoelectronic lighting.

Organosilicon-Based Ligand Design for High-Performance Perovskite Nanocrystal Films for Color Conversion and X-ray Imaging

Perovskite nanocrystals (PNCs) bear a huge potential for widespread applications, such as color conversion, X-ray scintillators, and active laser media. However, the poor intrinsic stability and high susceptibility to environmental stimuli including moisture and oxygen have become bottlenecks of PNC materials for commercialization. Appropriate barrier material design can efficiently improve the stability of the PNCs. Particularly, the strategy for packaging PNCs in organosilicon matrixes can integrate the advantages of inorganic-oxide-based and polymer-based encapsulation routes. However, the inert long-carbon-chain ligands (e.g., oleic acid, oleylamine) used in the current ligand systems for silicon-based encapsulation are detrimental to the cross-linking of the organosilicon matrix, resulting in performance deficiencies in the nanocrystal films, such as low transparency and large surface roughness. Herein, we propose a dual-organosilicon ligand system consisting of (3-aminopropyl)triethoxysilane (APTES) and (3-aminopropyl)triethoxysilane with pentanedioic anhydride (APTES-PA), to replace the inert long-carbon-chain ligands for improving the performance of organosilicon-coated PNC films. As a result, strongly fluorescent PNC films prepared by a facile solution-casting method demonstrate high transparency and reduced surface roughness while maintaining high stability in various harsh environments. The optimized PNC films were eventually applied in an X-ray imaging system as scintillators, showing a high spatial resolution above 20 lp/mm. By designing this promising dual organosilicon ligand system for PNC films, our work highlights the crucial influence of the molecular structure of the capping ligands on the optical performance of the PNC film.

APTES and CTAB Synergistic Induce a Heterozygous CsPbBr3/Cs4PbBr6 Perovskite Composite and its Application on the Sensitive Fluorescent Detection of Iodide ions

Recently, all-inorganic halide perovskite quantum dots (IPQD) as a new fluorescent material with excellent fluorescence properties have attracted wide attention. However, their instability in polar solvents is the main factor hindering their application in analysis. Herein, a heterozygous perovskite (CsPbBr3/Cs4PbBr6) was simultaneously prepared and stabilized by a silylanization strategy using (3-aminopropyl)-triethoxysilane (APTES) and cetyltrimethyl ammonium bromide (CTAB) assisted precipitation encapsulation method. The synthesized CsPbBr3/Cs4PbBr6 emitted an independent fluorescence at 520 nm. The obtained CsPbBr3/Cs4PbBr6 exhibited good stability in ethanol/water mixtures. It was used as a fluorescent probe for sensitively detecting iodide ions (I-) by fluorescence quenching mechanism in the concentration range of 1 ~ 70.0 µM with the detection limit (LOD) of 0.83 µM (relative standard deviation (RSD) = 1.33%, n = 20). The simplicity and high selectivity of the proposed fluorescent analysis method were the prominent features. This work could be extended to the other target ion detection by a perovskite fluorescent quenching.

Improving the stability of perovskite nanocrystals via SiO2 coating and their applications

Lead halide perovskite nanocrystals (LHP NCs) with outstanding optical properties have been regarded as promising alternatives to traditional phosphors for lighting and next-generation display technology. However, the practical applications of LHP NCs are seriously hindered by their poor stability upon exposure to moisture, oxygen, light, and heat. Hence, various strategies have been proposed to solve this issue. In this review, we have focused our attention on improving the stability of LHP NCs via SiO2 coating because it has the advantages of simple operation, less toxicity, and easy repetition. SiO2 coating is classified into four types: (a) in situ hydrolytic coating, (b) mesoporous silica loading, (c) mediated anchoring, and (d) double coating. The potential applications of SiO2-coated LHP NCs in the field of optoelectronics, biology, and catalysis are presented to elucidate the reliability and availability of SiO2 coating. Finally, the future development and challenges in the preparation of SiO2-coated LHP NCs are analyzed in order to promote the commercialization process of LHP NC-related commodities.

Water-stable, biocompatible, and highly luminescent perovskite nanocrystals-embedded fiber-based paper for anti-counterfeiting applications

In this study, we present a promising and facile approach toward the fabrication of non-toxic, water-stable, and eco-friendly luminescent fiber paper composed of polycaprolactone (PCL) polymer and CsPbBr₃@SiO₂ core-shell perovskite nanocrystals. PCL-perovskite fiber paper was fabricated using a conventional electrospinning process. Transmission electron microscopy (TEM) clearly revealed incorporation of CsPbBr₃@SiO₂ nanocrystals in the fibers, while scanning electron microscopy (SEM) demonstrated that incorporation of CsPbBr₃@SiO₂ nanocrystals did not affect the surface and diameter of the PCL-perovskite fibers. In addition, thermogravimetric analysis (TGA) and contact angle measurements have demonstrated that the PCL-perovskite fibers exhibit excellent thermal and water stability. The fabricated PCL-perovskite fiber paper exhibited a bright green emission centered at 520 nm upon excitation by ultra-violet (UV) light (374 nm). We have demonstrated that fluorescent PCL-perovskite fiber paper is a promising candidate for anti-counterfeiting applications because various patterns can be printed on the paper, which only become visible after exposure to UV light at 365 nm. Cell proliferation tests revealed that the PCL-perovskite fibers are cytocompatibility. Consequently, they may be suitable for biocompatible anti-counterfeiting. The present study reveals that PCL-perovskite fibers may pave way toward next generation biomedical probe and anti-counterfeiting applications.

Polymeric ionic liquid-based formulations for the fabrication of highly stable perovskite nanocrystal composites for photocatalytic applications

Halide perovskite nanocrystals (PNCs) have emerged as potential visible-light photocatalysts because of their outstanding intrinsic properties, including high absorption coefficient and tolerance to defects, which reduces non-radiative recombination, and high oxidizing/reducing power coming from their tuneable band structure. Nevertheless, their sensitivity to humidity, light, heat and water represents a great challenge that limits their applications in solar driven photocatalytic applications. Herein, we demonstrate the synergistic potential of embedding PNCs into polymeric ionic liquids (PILs@PS) to fabricate suitable composites for photodegradation of organic dyes. In this context, the stability of the PNCs after polymeric encapsulation was enhanced, showing better light, moisture, water and thermal stability compared to pristine PNCs for around 200 days.

Highly efficient silica coated perovskite nanocrystals with the assistance of ionic liquids for warm white LEDs

Given the inherent characteristics of defect-tolerant, tunable emission performance, and high extinction coefficient, lead halide perovskite nanocrystals (NCs) have attracted widespread attention as a promising material in optoelectronic fields. However, their poor structural stability greatly impedes their practical applications. Herein, a novel strategy for synthesizing stable CsPbBr₃@SiO₂ NCs via the hydrolytic polycondensation of (3-aminopropyl)triethoxysilane (APTES) in the presence of ionic liquids (ILs) is deliberately designed. The problems of fluorescence quenching and undesirable agglomeration of NCs resulting from ligand loss and surface erosion existing in common encapsulation methods can be effectively resolved. The fast and controllable growth of the SiO₂ shell around the CsPbBr₃ NCs is realized owing to the high polarity and hygroscopicity of the IL. Moreover, the dual effects of the IL for passivating the surface defects and avoiding the structural degradation of NCs during the hydrolysis process of APTES are demonstrated. As a result, CsPbBr₃@SiO₂ NCs with a high photoluminescence quantum yield of 85.7% and excellent stability are realized. Furthermore, this method proves to be a versatile tool to obtain CsPbX₃@SiO₂ NCs with different halide compositions, realizing a broad tunable wavelength from 421.2 nm to 651.6 nm. A warm white LED with a high color rending index was assembled through packaging CsPbBr₃@SiO₂ NCs and Cu-In-Zn-S/ZnS/PVP composites on a commercial blue chip. These findings are expected to facilitate the development of perovskite NCs, which provides access to their optoelectronic applications.

In situ passivation of Pb0 traps by fluoride acid-based ionic liquids enables enhanced emission and stability of CsPbBr3 nanocrystals for efficient white light-emitting diodes

A great hurdle restricting the optoelectronic applications of cesium lead halide perovskite (CsPbX₃) nanocrystals (NCs) is due to the uncoordinated lead atoms (Pb⁰) on the surface, where most attempts to address the challenges in the literature depend on complicated post-treatment processes. Here we report a simple in situ surface engineering strategy to obtain highly fluorescent and stable perovskite NCs, wherein the introduction of the multifunctional additive 1-butyl-3-methyl-imidazolium tetrafluoroborate ([Bmim]BF₄) can significantly eliminate the Pb⁰ traps. The photoluminescence quantum yield (PLQY) of the as-synthesized NCs was improved from 63.82% to 94.63% due to the good passivation of the surface defects. We also confirm the universality of this in situ passivation pathway to remove Pb⁰ deep traps by using fluoride acid-based ionic liquids (ILs). Due to the high hydrophobicity of the cations of ILs, the as-prepared CsPbBr₃ NCs exhibit robust water resistance stability, maintaining 67.5% of the initial photoluminescence (PL) intensity after immersion in water for 21 days. A white light emitting diode (LED), assembled by mixing the as-synthesized CsPbBr₃ NCs and red K₂SiF₆:Mn⁴⁺ phosphors onto a blue chip, exhibits high luminous efficiency (100.07 lm W^-1) and wide color gamut (140.64% of the National Television System Committee (NTSC) standard). This work provides a promising and facile technique to eliminate the Pb⁰ traps and improve the optical performance and stability of halide perovskite NCs, facilitating their applications in optoelectronic fields.

4-Bromo-Butyric Acid-Assisted In Situ Passivation Strategy for Superstable All-Inorganic Halide Perovskite CsPbX3 Quantum Dots in Polar Media

A crucial challenge is to develop an in situ passivation treatment strategy for CsPbX₃ (CPX, X=Cl, Br, and I) quantum dots (QDs) and simultaneously retain their luminous efficiency and wavelength. Here, a facile method to significantly improve the stability of the CPX QDs via in situ crystallization with the synergistic effect of 4-bromo-butyric acid (BBA) and oleylamine (OLA) in polar solvents including aqueous solution and a possible fundamental mechanism are proposed. Monodispersed CsPbBr₃ (CPB) QDs obtained in water show high photoluminescence quantum yields (PLQYs) of 86.4 % and their PL features of CPB QDs have no significant change after being dispersed in aqueous solution for 96 h, which implies the structure of CPB QDs is unchanged. The results provide a viable design strategy to synthesize all-inorganic perovskite CPX QDs with strong stability against the attack of polar solvents and shed more light on their surface chemistry.

Synergetic effect of the surface ligand and SiO2 driven photoluminescence stabilization of the CH3NH3PbBr3 perovskite magic-sized clusters

Zero-dimensional Perovskite Magic-size Clusters play crucial roles in understanding and controlling nucleation and growth of semiconductor nanoparticles. However, their metastability behavior is a critical hindrance for reliable characterizations. Here, we report the first demonstration of using an excess amount of surface ligand and SiO₂ as novel passivation for synthesizing the magic-sized clusters (MSCs) by the Ligand-assisted reprecipitation method. A synergetic effect between an excessed surface ligand and SiO₂ inhibits the protonation and deprotonation reaction between amine-based and acid-based ligand, leading to enhanced PL stability. The obtained CH₃NH₃PbBr₃ PMSCs/SiO₂ retain 70% of its initial emission intensity in ambient conditions for 20 days. This passivation approach opens an entirely new avenue for the reliable characterizations of CH₃NH₃PbBr₃ PMSCs, which will significantly broaden their application for understanding and controlling nucleation and growth of semiconductor nanoparticles.

Alloyed Green-Emitting CdZnSeS/ZnS Quantum Dots with Dense Protective Layers for Stable Lighting and Display Applications

Alloyed green-emitting CdZnSeS/ZnS quantum dots (QDs) demonstrate potential applications in solid-state lighting and displays owing to their various advantages, such as high color purity, light conversion efficiency, and color rendering index. However, their applications in white light-emitting diodes (WLEDs) are limited by their poor photostabilities on blue-emitting gallium nitride (GaN) LED chips. In this study, the effect of the specific surface area (SSA) in the coating layers on the photostabilities of QDs was investigated. SSA was adjusted by controlling the proportions of dense aluminum oxide (AlO_X) layers and porous silica dioxide (SiO₂) layers to fabricate QD protective layers via a catalyst-free sol-gel method. The results showed that the synthesized AlO_X possessing the lowest SSA among the synthesis protective layers presented the best QD photostabilities on the LED chips. Moreover, they exhibited a 9.9-fold increase in the operational lifetime (T₈₀) compared to that of pristine QDs. In addition, the QD-based WLED achieved an excellent display performance with a wide color gamut (115%) of the National Television System Committee (NTSC) color gamut standard. This approach offers a promising strategy for enhancing the QD photostabilities for applications in solid-state lighting and displays by coating the protective layers on the QD surface.

Highly Photoluminescent CsPbBr3/CsPb2Br5 NCs@TEOS Nanocomposite in Light-Emitting Diodes

All-inorganic halide perovskite (CsPb₂Br₅) nanocrystals (NCs) have received widespread attention owing to their unique photoelectric properties. This work reports a novel strategy to control the phase transition from CsPbBr₃ to CsPb₂Br₅ and investigates the effects of different treatment times and treatment temperatures on perovskite NCs formation. By controlling the volume of tetraethoxysilane (TEOS) added, the formation of different phases of perovskite powder can be well controlled. In addition, a white light-emitting diode (WLED) device is designed by coupling the CsPbBr₃/CsPbBr₃-CsPb₂Br₅ NCs@TEOS nanocomposite and CaAlSiN₃:Eu²⁺ commercial phosphor with a 460 nm InGaN blue chip, exhibiting a high luminous efficiency of 57.65 lm/W, color rendering index (CRI) of 91, and a low CCT of 5334 K. The CIE chromaticity coordinates are (0.3363, 0.3419). This work provides a new strategy for the synthesis of CsPbBr₃/CsPbBr₃-CsPb₂Br₅ NCs@TEOS nanocomposite, which can be applied to the field of WLEDs and display devices.

Interface Chemical Modification between All-Inorganic Perovskite Nanocrystals and Porous Silica Microspheres for Composite Materials with Improved Emission

In recent years, there has been rapid progress in the development of photonic devices based on lead halide perovskite nanocrystals since they possess a set of unique optical and charge transport properties. However, the main limiting factor for their subsequent application is poor stability against exposure to adverse environmental conditions. In this work, a study of a composite material based on perovskite CsPbBr3 nanocrystals embedded in porous silica microspheres is presented. We developed two different approaches to change the interface between nanocrystals and the surface of the microsphere pores: surface treatment of (i) nanocrystals or (ii) microspheres. The surface modification with tetraethylorthosilicate molecules not only increased stability but also improved the optical responses of the composite material. The position of the emission band remained almost unchanged, but its lifetime increased significantly compared to the initial value. The improvement of the optical performance via surface modification with tetraethylorthosilicate molecules also works for the lead-free Bi-doped Cs2AgInCl6 double perovskite nanocrystals leading to increased stability of their optical responses at ambient conditions. These results clearly demonstrate the advantage of a composite material that can be used in novel photonic devices with improved performance.

Highly luminescent biocompatible CsPbBr3@SiO2 core-shell nanoprobes for bioimaging and drug delivery

The encapsulation of lead halide perovskite nanocrystals (PNCs) with an inert protective layer against moisture and the environment is a promising approach to overcome hinderances for their practical use in optoelectronic and biomedical applications. Herein, a facile method for synthesizing highly luminescent and biocompatible CsPbBr₃@SiO₂ core-shell PNCs with a controlled SiO₂ thickness, which are suitable for both cell imaging and drug delivery, is reported. The synthesized CsPbBr₃@SiO₂ core-shell PNCs exhibit bright green emission at 518 nm upon excitation of 374 nm. Interestingly, a significant increase in the photoluminescence intensity is observed with an increase in the SiO₂ shell thickness, which varies with the increasing reaction time. Cytotoxicity results indicate that the CsPbBr₃@SiO₂ core-shell PNCs are nontoxic, making them suitable for in vitro cell imaging using HeLa cells. Furthermore, doxorubicin physically adsorbed on the surface of CsPbBr₃@SiO₂ core-shell PNCs is efficiently released in cells when the drug-loaded perovskite nanoprobes are injected in the cells, indicating that these core-shell nanoparticles can be used for drug loading and delivery. The results of this study suggest that the CsPbBr₃@SiO₂ core-shell PNCs can pave the way for new biomedical applications and processes.