Trioctylphosphine-Assisted Pre-protection Low-Temperature Solvothermal Synthesis of Highly Stable CsPbBr3/TiO2 Nanocomposites

Continuous-flow synthesis of CsPbI3/TiO2 nanocomposites with enhanced water and thermal stability

The inherent poor stability of CsPbI3 nanocrystals hinders the practical application of this material. Therefore, it is still a challenge to improve the stability of CsPbI3 nanocrystals and realize their large-scale continuous preparation. In this work, we report the preparation of CsPbI3/TiO2 nanocomposites with high stability by a microfluidic method. After the combination of CsPbI3 nanorods with TiO2, the PL intensity increased by 1.3 times under excitation at 577 nm due to the passivating effect of TiO2 on the surface of CsPbI3 nanorods and its carrier transport characteristics. Meanwhile, due to the coating of TiO2, the surface exposure area of CsPbI3 nanorods is reduced, which blocks external environmental effects to some extent and effectively improves the stability of CsPbI3 nanorods. Finally, an LED with a color gamut of 142% NTSC and a color temperature (CCT) of 3952 K was obtained by combining CsPbI1.5Br1.5/TiO2 and CsPbBr3/TiO2 nanocomposites with a blue light chip (455 nm). This study shows that the continuous and controllable synthesis of all inorganic halide perovskite nanocrystals by a microfluidic method is of great significance in the fabrication of high-performance optoelectronic materials and display devices.

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.

Recent Advances and Perspectives of Metal Halide Perovskite Heteronanocrystals

Heteronanocrystals that combine multiple semiconductors into a nanoscale heterostructure possess excellent optical performance and flexibility in property engineering compared with their single-component counterparts. The successes in fabricating lead halide perovskite-based heteronanocrystals (PHNCs) have drastically improved the stability and tunability of the optical and electrical properties. However, the epitaxial growth of semiconductor materials on perovskite nanocrystals remains a fundamental challenge because of the mismatch in their surface structure and crystal growth kinetics. Here, we review recent progress in the development of PHNCs with emphasis on their synthesis methods and surface chemistry that led to new insights and reaction protocols for the design and fabrication of PHNCs. In addition, the optical features of different types of PHNCs and nanocomposites and their application perspectives are summarized. Finally, we conclude with a discussion of the remaining issues, challenges, and opportunities in epitaxial growth of Janus and core-shell structure PHNCs.

Influence of Different Capping Agents on the Structural, Optical, and Photocatalytic Degradation Efficiency of Magnetite (Fe3O4) Nanoparticles

Octylamine (OTA), 1-dodecanethiol (DDT), and tri-n-octylphosphine (TOP) capped magnetite nanoparticles were prepared by co-precipitation method. Powder X-ray diffraction patterns confirmed inverse spinel crystalline phases for the as-prepared iron oxide nanoparticles. Transmission electron microscopic micrographs showed iron oxide nanoparticles with mean particle sizes of 2.1 nm for Fe₃O₄-OTA, 5.0 nm for Fe₃O₄-DDT, and 4.4 nm for Fe₃O₄-TOP. The energy bandgap of the iron oxide nanoparticles ranges from 2.25 eV to 2.76 eV. The iron oxide nanoparticles were used as photocatalysts for the degradation of methylene blue with an efficiency of 55.5%, 58.3%, and 66.7% for Fe₃O₄-OTA, Fe₃O₄-DDT, and Fe₃O₄-TOP, respectively, while for methyl orange the degradation efficiencies were 63.8%, 47.7%, and 74.1%, respectively. The results showed that tri-n-octylphosphine capped iron oxide nanoparticles are the most efficient iron oxide nano-photocatalysts for the degradation of both dyes. Scavenger studies show that electrons (e^-) and hydroxy radicals (•OH) contribute significantly to the photocatalytic degradation reaction of both methylene blue and methyl orange using Fe₃O₄-TOP nanoparticles. The influence of the dye solution's pH on the photocatalytic reaction reveals that a pH of 10 is the optimum for methylene blue degradation, whereas a pH of 2 is best for methyl orange photocatalytic degradation using the as-prepared iron oxide nano-photocatalyst. Recyclability studies revealed that the iron oxide photocatalysts can be recycled three times without losing their photocatalytic activity.

Preparation of CsPb(Cl/Br)3/TiO2:Eu3+ composites for white light emitting diodes

The inherent single narrow emission peak and fast anion exchange process of cesium lead halide perovskite CsPbX₃ (X = Cl, Br, I) nanocrystals severely limited its application in white light-emitting diodes. Previous studies have shown that composite structures can passivate surface defects of NCs and improve the stability of perovskite materials, but complex post-treatment processes commonly lead to dissolution of NCs. In this study, CsPb(Cl/Br)₃ NCs was in-situ grown in TiO₂ hollow shells doped with Eu³⁺ ions by a modified thermal injection method to prepare CsPb(Cl/Br)₃/TiO₂:Eu³⁺ composites with direct excitation of white light without additional treatment. Among them, the well-crystalline TiO₂ shells acted as both a substrate for the dopant, avoiding the direct doping of Eu³⁺ into the interior of NCs to affect the crystal structure of the perovskite materials, and also as a protection layer to isolate the contact between PL quenching molecules and NCs, which significantly improves the stability. Further, the WLED prepared using the composites had bright white light emission, luminous efficiency of 87.39 lm/W, and long-time operating stability, which provided new options for the development of perovskite devices.

Sr2+doped CsPbBrI2perovskite nanocrystals coated with ZrO2for applications as white LEDs

Perovskite nanocrystals (NCs) feature adjustable bandgap, wide absorption range, and great color purity for robust perovskite optoelectronic applications. Nevertheless, the absence of lasting stability under continues energization, is still a major hurdle to the widespread use of NCs in commercial applications. In particular, the reactivity of red-emitting perovskites to environmental surroundings is more sensitive than that of their green counterparts. Here, we present a simple synthesis of ultrathin ZrO₂coated, Sr²⁺doped CsPbBrI₂NCs. Introducing divalent Sr²⁺may significantly eliminate Pb° surface traps, whereas ZrO₂encapsulation greatly improves environmental stability. The photoluminescence quantum yield of the Sr²⁺-doped CsPbBrI₂/ZrO₂NCs was increased from 50.2% to 87.2% as a direct consequence of the efficient elimination of Pb° surface defects. Moreover, the thickness of the ZrO₂thin coating gives remarkable heat resistance and improved water stability. Combining CsPbSr_0.3BrI₂/ZrO₂NCs in a white light emitting diode (LED) with an excellent optical efficiency (100.08 lm W^-1), high and a broad gamut 141% (NTSC) standard. This work offers a potential method to suppress Pb° traps by doping with Sr²⁺and improves the performance of perovskite NCs by ultrathin coating structured ZrO₂, consequently enabling their applicability in commercial optical displays.

High-Entropy Spinel Ferrites with Broadband Wave Absorption Synthesized by Simple Solid-Phase Reaction

In this work, high-entropy (HE) spinel ferrites of (FeCoNiCrM)_xO_y (M = Zn, Cu, and Mn) (named as HEO-Zn, HEO-Cu, and HEO-Mn, respectively) were synthesized by a simple solid-phase reaction. The as-prepared ferrite powders possess a uniform distribution of chemical components and homogeneous three-dimensional (3D) porous structures, which have a pore size ranging from tens to hundreds of nanometers. All three HE spinel ferrites exhibited ultrahigh structural thermostability at high temperatures even up to 800 °C. What is more, these spinel ferrites showed considerable minimum reflection loss (RL_min) and significantly enhanced effective absorption bandwidth (EAB). The RL_min and EAB values of HEO-Zn and HEO-Mn are about -27.8 dB at 15.7 GHz, 6.8 GHz, and -25.5 dB at 12.9 GHz, 6.9 GHz, with the matched thickness of 8.6 and 9.8 mm, respectively. Especially, the RL_min of HEO-Cu is -27.3 dB at 13.3 GHz with a matched thickness of 9.1 mm, and the EAB reaches about 7.5 GHz (10.5-18.0 GHz), which covers almost the whole X-band range. The superior absorbing properties are mainly attributed to the dielectric energy loss involving interface polarization and dipolar polarization, the magnetic energy loss referring to eddy current and natural resonance loss, and the specific functions of 3D porous structure, indicating a potential application prospect of the HE spinel ferrites as EM absorbing materials.

Preparation of ultra-stable and environmentally friendly CsPbBr3@ZrO2/PS composite films for white light-emitting diodes

The working stability of perovskite light-emitting diodes (LEDs) has become an urgent bottleneck to be solved in the process of commercialization. Although lead halide perovskite CsPbX₃ (X = Br, I, Cl) quantum dots (QDs) are considered rising stars in the lighting market owing to their excellent optoelectronic properties, they suffer from fluorescence quenching under thermal conditions. Unfortunately, the surfaces of electronic devices inevitably warm up under long-term energization, which is extremely detrimental to the appropriate functioning of CsPbX₃ QDs. Based on the above discussion, the relationship function between the energization time and surface temperature of electronic devices was analyzed, after which a strategy for the preparation of dual-encapsulating perovskites using organic (polystyrene (PS)) and inorganic (ZrO₂) materials was proposed, and the change in optical stability before and after encapsulation was investigated. The results show that the thermal stability of CsPbBr₃@ZrO₂/PS composite films (CFs) after the dual encapsulation was remarkably enhanced, and the assembled white LEDs still retain the initial emission intensity under prolonged high-power operation. In addition, the double encapsulation layer completely suppresses the ion leakage in CsPbBr₃ and avoids damage to the ecosystem. It can be seen that this encapsulation strategy was capable of imparting excellent working stability to the perovskite material, which would clear the obstacles to commercial conversion.

Enhanced photoluminescence stability and internal defect evolution of the all-inorganic lead-free CsEuCl3 perovskite nanocrystals

Perovskite materials are prominent candidates for many high-performance optoelectronic devices. The rare-earth lead-free CsEuCl₃ perovskite nanocrystals are extremely unstable, which makes it very difficult to study their physicochemical properties and applications. Herein, we improved the stability of rare-earth based CsEuCl₃ nanocrystals by employing a silica-coating for the first time. Simultaneously, the naturally formed "hollow" regions with an obviously blue-shifted PL emission were first observed inside the CsEuCl₃ nanocrystals during the period of storage. Density functional theory (DFT) calculations showed that the formed "hollow" regions are due to the internal defect evolution in the perovskite lattice, which is also responsible for the increase of the bandgap and the blue-shift of emission. Additionally, the rapid decline of luminescence is probably due to the nanocrystals' final cracking with the expansion of the "hollow" regions. This work helps to understand the relationship between defects and luminescence properties, and provides guidance for the design of more stable lead-free perovskite nanocrystals.

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.

Strong violet emission from ultra-stable strontium-doped CsPbCl3 superlattices

Among the lead halide perovskites, the photoluminescence quantum yields (PLQYs) of perovskite quantum dots (PQDs) in the violet region are the very lowest. This is an obstacle to the optical applications across the entire visible area based on perovskite materials. Herein, we report a novel strontium (Sr)-substitution along with chlorine passivation strategy to enhance the PLQYs of CsPbCl₃ PQDs. We surprisingly found that when the molar ratio of Sr²⁺/Pb²⁺ = 0.1/0.9, CsSr_0.1Pb_0.9Cl₃ PQDs exhibit strong single-color violet emission, which is attributed to the effective passivation of chlorine defects. We further found spontaneous self-assembly of PQDs into highly emissive PSCs from the precursor in a highly concentrated solution. Moreover, by dilution of these PSCs, a few small PQD aggregates can be regained, which is similar to the PQDs formed at lower concentrations. Benefiting from the superior collective properties of individual PQDs, these highly fluorescent CsSr_0.1Pb_0.9Cl₃ PSCs can maintain good stability even when directly immersed in water or exposed to illumination.

Tuning optical properties of CsPbBr3by mixing Nd3+trivalent lanthanide halide cations for blue light emitting devices

In recent years, significant progress has been made in the red and green perovskite quantum dots (PQDs) based light-emitting devices. However, a scarcity of blue-emitting devices that are extremely efficient precludes their research and development for optoelectronic applications. Taking advantage of tunable bandgaps of PQDs over the entire visible spectrum, herein we tune optical properties of CSPbBr₃by mixing Nd³⁺trivalent lanthanide halide cations for blue light-emitting devices. The CsPbBr₃PQDs doped with Nd³⁺trivalent lanthanide halide cations emitted strong photoemission from green into the blue region. By adjusting their doping concentration, a tunable wavelength from (515 nm) to (450 nm) was achieved with FWHM from (37.83 nm) to (16.6 nm). We simultaneously observed PL linewidth broadening thermal quenching of PL and the blue shift of the optical bandgap from temperature-dependent PL studies. The Nd³⁺cations into CsPbBr₃PQDs more efficiently reduced non-radiative recombination. As a result of the efficient removal of defects from PQDs, the photoluminescence quantum yield (PLQY) has been significantly increased to 91% in the blue-emitting region. Significantly, Nd³⁺PQDs exhibit excellent long-term stability against the external environment, including water, temperature, and ultraviolet light irradiation. Moreover, we successfully transformed Nd³⁺doped PQDs into highly fluorescent nanocomposites. Incorporating these findings, we fabricate and test a stable blue light-emitting LED with EL emission at (462 nm), (475 nm), and successfully produce white light emission from Nd³⁺doped nanocomposites with a CIE at (0.32, 0.34), respectively. The findings imply that low-cost Nd³⁺doped perovskites may be attractive as light converters in LCDs with a broad color gamut.