Ultrafast Thermodynamic Control for Stable and Efficient Mixed Halide Perovskite Nanocrystals

Low photoluminescence quantum yield (PLQY) and spectra instability, the two most difficult challenges in blue‐emitting CsPbBr_xCl_3?x NCs, have not yet been solved. Quickly controlling the reaction thermodynamics is crucial to enhance crystallinity, thus PLQY and spectra stability, but it has been ignored until now. An ultrafast thermodynamic control (UTC) strategy is designed by utilizing liquid nitrogen to instantaneously freeze the superior crystal lattices of CsPbBr_xCl_3?x NCs formed at high temperature. The average cooling rate exhibits a 33‐fold increase compared to conventional ice‐water cooling (from 1.5 to 50 K s^?1). This UTC can make the reaction thermodynamic energy of the system lower than the threshold very quickly. Therefore, abrupt termination of further crystal growth can be achieved, which also avoids additional nucleation at low temperature. With the assist of defect passivation, the final blue‐emitting CsPbBr_xCl_3?x NCs exhibit an absolute PLQY of 98%, representing the highest value in Pb‐based blue perovskites to date. More importantly, they exhibit superior spectra instability. This UTC strategy not only represents a new avenue to synthesize perovskite NCs with excellent crystal quality and ultrahigh PLQY, but also provides a good reference to deal with the recognized bottleneck of spectra instability.     

Synthesis and spectroscopic characterization of CsPbBr3/Cs4PbBr6 perovskites synthesized via the microwave-assisted heating process for backlight display devices

In this study, CsPbBr₃/Cs₄PbBr₆ composites were prepared via microwave-assisted (MA) and conventional heating (CH) routes. X-ray diffraction and high-resolution transmission electron microscopy confirmed the coexistence of CsPbBr₃ and Cs₄PbBr₆ phases in the prepared samples. The steady-state absorption spectra of the synthesized perovskites exhibited excitonic peaks at 310 and 525 nm because of the absorption of Cs₄PbBr₆ and CsPbBr₃, respectively. The prepared samples exhibited characteristic emission peaks at approximately 523 nm. The MA-derived sample exhibited high color purity (94%), high quantum yield (89%), and good thermal stability (>98% after 100 h of treatment). By contrast, the CH-derived sample exhibited low color purity (91%) and quantum yield (70%). Furthermore, microwave irradiation with polar molecules in MA heating resulted in the rapid generation of homogeneous heat within the heated materials, which induced the substantial nucleation and growth of CsPbBr₃. This phenomenon enhanced intensity of photoluminescence emission. The MA-derived sample exhibited a shorter excitonic lifetime (20 ns) than the CH-derived sample did (32 ns) because the MA-derived sample had less nonradiative trap sites. The color gamut of the as-prepared light-emitting devices fabricated with the MA-derived sample was 125% of the NTSC. This study indicated that the incorporation of microwave heating in the synthesis process is an effective approach for preparing CsPbBr₃/Cs₄PbBr₆ composites with a wide color gamut, good thermal stability, and a PLQY.     

Core/Shell Perovskite Nanocrystals: Synthesis of Highly Efficient and Environmentally Stable FAPbBr3/CsPbBr3 for LED Applications

Lead halide perovskite nanocrystals (PeNCs) are promising materials for applications in optoelectronics. However, their environmental instability remains to be addressed to enable their advancement into industry. Here the development of a novel synthesis method is reported for monodispersed PeNCs coated with all inorganic shell of cesium lead bromide (CsPbBr₃) grown epitaxially on the surface of formamidinium lead bromide (FAPbBr₃) NCs. The formed FAPbBr₃/CsPbBr₃ NCs have photoluminescence in the visible range 460–560 nm with narrow emission linewidth (20 nm) and high optical quantum yield, photoluminescence quantum yield (PLQY) up to 93%. The core/shell perovskites have enhanced optical stability under ambient conditions (70 d) and under ultraviolet radiation (50 h). The enhanced properties are attributed to overgrowth of FAPbBr₃ with all‐inorganic CsPbBr₃ shell, which acts as a protective layer and enables effective passivation of the surface defects. The use of these green‐emitting core/shell FAPbBr₃/CsPbBr₃ NCs is demonstrated in light‐emitting diodes (LEDs) and significant enhancement of their performance is achieved compared to core only FAPbBr₃‐LEDs. The maximum current efficiency observed in core/shell NC LED is 19.75 cd A^‐1 and the external quantum efficiency of 8.1%, which are approximately four times and approximately eight times higher, respectively, compared to core‐only devices.     

Enhanced performance of inverted CsPbBr3 nanocrystal LEDs via Zn(II) doping

Perovskite lighting-emitting diodes (PeLEDs) with inverted structure have been considered as promising display technology due to their suitable driving schemes with n-type thin-film transistors. However, the defects and imbalanced charge carriers in the CsPbBr₃ nanocrystal (NC) PeLED are key hurdles, limiting the performance. Herein, we have successfully doped Zn²⁺ ions into CsPbBr₃ NCs by ligand-assisted reprecipitation method, exhibiting an 85% enhancement of the photoluminescence quantum yield (PLQY). In addition, the optimized energy level alignment via Zn doping facilitates the carrier balance in the devices, improving the efficiencies. The obtained CsPbBr₃:Zn-based PeLED reaches a high luminance of 3124 cd/m² and a maximum external quantum efficiency (EQE) of 0.85%, which are superior to those of CsPbBr₃-based PeLED (luminance = 564 cd/m², EQE = 0.09%). The results demonstrate that Zn doping significantly enhances the performance of PeLED, which increases the potential of these inverted PeLEDs connected with n-type TFTs towards practical applications.     

Enhanced Optical Properties and Stability of CsPbBr3 Nanocrystals Through Nickel Doping

To improve the quantum efficiency and stability of perovskite quantum dots, the structural and optical properties are optimized by varying the concentration of Ni doping in CsPbBr₃ perovskite nanocrystals (PNCs). As Ni doping is gradually added, a blue shift is observed at the photoluminescence (PL) spectra. Ni-doped PNCs exhibit stronger light emission, higher quantum efficiency, and longer lifetimes than undoped PNCs. The doped divalent element acts as a defect in the perovskite structure, reducing the recombination rate of electrons and holes. A stability test is used to assess the susceptibility of the perovskite to light and moisture. For ultra-violet light irradiation, the PL intensity of undoped PNCs decreases by 70%, whereas that of Ni-doped PNCs decreases by 18%. In the water addition experiment, the PL intensity of Ni-doped PNCs is three times that of undoped PNCs. For CsPbBr₃ and Ni:CsPbBr₃ PNCs, a light emitting diode is fabricated by spin-coating. The efficiency of Ni:CsPbBr₃ exceeds that of CsPbBr₃ PNCs, and the results significantly differ based on the ratio. A maximum luminance of 833 cd m^–2 is obtained at optimum efficiency (0.3 cd A^–1). Therefore, Ni-doped PNCs are expected to contribute to future performance improvements in display devices.     

Photoelectrochemically Active and Environmentally Stable CsPbBr3/TiO2 Core/Shell Nanocrystals

Inherent poor stability of perovskite nanocrystals (NCs) is the main impediment preventing broad applications of the materials. Here, TiO₂ shell coated CsPbBr₃ core/shell NCs are synthesized through the encapsulation of colloidal CsPbBr₃ NCs with titanium precursor, followed by calcination at 300 °C. The nearly monodispersed CsPbBr₃/TiO₂ core/shell NCs show excellent water stability for at least three months with the size, structure, morphology, and optical properties remaining identical, which represent the most water‐stable inorganic shell passivated perovskite NCs reported to date. In addition, TiO₂ shell coating can effectively suppress anion exchange and photodegradation, therefore dramatically improving the chemical stability and photostability of the core CsPbBr₃ NCs. More importantly, photoluminescence and (photo)electrochemical characterizations exhibit increased charge separation efficiency due to the electrical conductivity of the TiO₂ shell, hence leading to an improved photoelectric activity in water. This study opens new possibilities for optoelectronic and photocatalytic applications of perovskites‐based NCs in aqueous phase.     

One-Step Polymeric Melt Encapsulation Method to Prepare CsPbBr3 Perovskite Quantum Dots/Polymethyl Methacrylate Composite with High Performance

All-inorganic CsPbBr₃ perovskite quantum dots (PQDs) exhibit excellent photoelectric properties and application prospects in the field of light-emitting diodes (LEDs) and display devices. However, these possess poor long-term stability to UV irradiation, water, heat, and oxygen. Using polymethyl methacrylate (PMMA) as the matrix along with CH₃(CH₂)₁₆COOCs, [CH₃(CH₂)₁₆COO]₂Pb, and KBr as the perovskite sources, CsPbBr₃ PQDs/PMMA composites are for the first time prepared via an in situ polymeric melt encapsulation method. Special attention is paid to the effects of synthesis conditions on the photoluminescent quantum yield (PLQY) of the composites. The optimized CsPbBr₃ PQDs/PMMA composite reveals excellent performance with ≈82.7% PLQY and ≈18.6 nm full width at a half-maximum (FWHM). In particular, after 90 h of UV irradiation or 35 days of heating at 60 °C, the luminous intensity remains almost unchanged. In addition, after soaking in water for 15 days, it retains up to ≈53% of the initial luminous intensity, meaning that the composite possesses long-term stability to UV irradiation, heat, and water. The as-prepared white LED (WLED) based on the composite evidences the wide color gamut (126.5% National Television System Committee (NTSC)) and a luminous efficiency of 32 lm W⁻¹. This work offers a novel, easily industrialized one-step, and solvent free route for low-temperature synthesis of all-inorganic PQDs with broad application prospects.     

Deconvoluting Energy Transport Mechanisms in Metal Halide Perovskites Using CsPbBr3 Nanowires as a Model System

Understanding energy transport in metal halide perovskites is essential to effectively guide further optimization of materials and device designs. However, difficulties to disentangle charge carrier diffusion, photon recycling, and photon transport have led to contradicting reports and uncertainty regarding which mechanism dominates. In this study, monocrystalline CsPbBr₃ nanowires serve as 1D model systems to help unravel the respective contribution of energy transport processes in metal-halide perovskites. Spatially, temporally, and spectrally resolved photoluminescence (PL) microscopy reveals characteristic signatures of each transport mechanism from which a robust model describing the PL signal accounting for carrier diffusion, photon propagation, and photon recycling is developed. For the investigated CsPbBr₃ nanowires, an ambipolar carrier mobility of μ = 35 cm² V⁻¹ s⁻¹ is determined, and is found that charge carrier diffusion dominates the energy transport process over photon recycling. Moreover, the general applicability of the developed model is demonstrated on different perovskite compounds by applying it to data provided in previous related reports, from which clarity is gained as to why conflicting reports exist. These findings, therefore, serve as a useful tool to assist future studies aimed at characterizing energy transport mechanisms in semiconductor nanowires using PL.     

Facile method for the preparation of high-performance photodetectors with a GQDs/perovskite bilayer heterostructure

A high-performance nitrogen doped graphene quantum dots (GQDs)/all-inorganic (CsPbBr₃) perovskite nanocrystals (NCs) heterostructure photodetector was fabricated on a quartz substrate, using the low cost spin coating technique followed by hot plate annealing. The GQDs/CsPbBr₃ NCs heterostructure photodetector exhibits a high overall performance with a photoresponsivity of 0.24 AW⁻¹, on/off ratio of 7.2 × 10⁴, and specific detectivity of up to 2.5 × 10¹² Jones. The on/off ratio of the hybrid device was improved by almost ten orders of magnitude, and the photoresponsivity was enhanced almost three times compared to the single layer perovskite NCs photodetector. The performance enhancement of the hybrid device was due to its highly efficient carrier separation at the GQDs/CsPbBr₃ NCs interface. This results from the coupling of the GQDs layer, which efficiently extracts and transports the photogenerated carriers, with the CsPbBr₃ NCs layer, which has a large absorption coefficient and high quantum efficiency. The interfacial charge transfer from the CsPbBr₃ NCs to the GQDs layer was demonstrated by the quenching in the photoluminescence (PL) spectra, and the fast-average decay time in the time-resolved photoluminescence (Trpl) spectra of the hybrid photodetector. Moreover, the performance-enhancement mechanism of the hybrid GQDs/CsPbBr₃ photodetector was elucidated by analyzing the band alignment of the GQDs and CsPbBr₃ under laser illumination.     

All-Inorganic CsPbBr3 Perovskite Nanocrystals/2D Non-Layered Cadmium Sulfide Selenide for High-Performance Photodetectors by Energy Band Alignment Engineering

Perovskites have attracted intensive attention as promising materials for the application in various optoelectronic devices due to their large light absorption coefficient, high carrier mobility, and long charge carrier diffusion length. However, the performance of the pure perovskite nanocrystals-based device is extremely restricted by the limited charge transport capability due to the existence of a large number of the grain boundary between perovskite nanocrystals. To address these issues, a high-performance photodetector based on all-inorganic CsPbBr₃ perovskite nanocrystals/2D non-layered cadmium sulfide selenide heterostructure has been demonstrated through energy band engineering with designed typed-II heterostructure. The photodetector exhibits an ultra-high light-to-dark current ratio of 1.36 × 10⁵, a high responsivity of 2.89 × 10² A W⁻¹, a large detectivity of 1.28 × 10¹⁴ Jones, and the response/recovery time of 0.53s/0.62 s. The enhancement of the optoelectronic performance of the heterostructure photodetector is mainly attributed to the efficient charge carrier transfer ability between the all-inorganic CsPbBr₃ perovskites and 2D cadmium sulfide selenide resulting from energy band alignment engineering. The charge carriers’ transfer dynamics and the mechanism of the CsPbBr₃ perovskites/2D non-layered nanosheets interfaces have also been studied by state-state PL spectra, fluorescence lifetime imaging microscopy, time-resolved photoluminescence spectroscopy, and Kelvin probe force microscopy measurements.     

Ultrastable and Reversible Fluorescent Perovskite Films Used for Flexible Instantaneous Display

All‐inorganic halide perovskite materials are regarded as promising materials in information display applications owing to their tunable color, narrow emission peak, and easy processability. However, the photoluminescence (PL) stability of halide perovskite films is still inferior due to their poor thermal stability and hygroscopic properties. Herein, all‐inorganic perovskite films are prepared through vacuum thermal deposition method to enhance thermal and hygroscopic stability. By intentionally adding extra bromide source, a structure of CsPbBr₃ nanocrystals embedded in a CsPb₂Br₅ matrix (CsPbBr₃/CsPb₂Br₅) is formed via an air exposure process, leading to impressive PL stability in ambient atmosphere. In addition, the as‐fabricated CsPbBr₃/CsPb₂Br₅ structure shows enhanced PL intensity due to the dielectric confinement. The CsPbBr₃/CsPb₂Br₅ structure film can almost reserve its initial PL intensity after four months, even stored in ambient atmosphere. The PL intensity for CsPbBr₃/CsPb₂Br₅ films vanishes at elevated temperature and recovers by cooling down in a short time. The reversible PL conversion process can be repeated over hundreds of times. Based on the reversible PL property, prototype thermal‐driven information display devices are demonstrated by employing heating circuits on flexible transparent substrates. These robust perovskite films with reversible PL characteristics promise an alternative solid‐state emitting display.     

Pure Blue Electroluminescence by Differentiated Ion Motion in a Single Layer Perovskite Device

Blue electroluminescence is highly desired for emerging light-emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve, particularly in mixed-halide perovskites, where intrinsic ion motion and halide segregation compromises spectral purity. Here, CsPbBr_3−xCl_x perovskites, polyelectrolytes, and a salt additive are leveraged to demonstrate pure blue emission from single-layer light-emitting electrochemical cells (LECs). The electrolytes transport the ions from salt additives, enhancing charge injection and stabilizing the inherent perovskite emissive lattice for highly pure and sustained blue emission. Substituting Cl into CsPbBr₃ tunes the perovskite luminescence from green through blue. Sky blue and saturated blue devices produce International Commission on Illumination coordinates of (0.105, 0.129) and (0.136, 0.068), respectively, with the latter meeting the US National Television Committee standard for the blue primary. Likewise, maximum luminances of 2900 and 1000 cd m⁻², external quantum efficiencies (EQEs) of 4.3% and 3.9%, and luminance half-lives of 5.7 and 4.9 h are obtained for sky blue and saturated blue devices, respectively. Polymer and LiPF₆ inclusion increases photoluminescence efficiency, suppresses halide segregation, induces thin-film smoothness and uniformity, and reduces crystallite size. Overall, these devices show superior performance among blue perovskite light-emitting diodes (PeLEDs) and general LECs.     

2D Derivative Phase Induced Growth of 3D All Inorganic Perovskite Micro–Nanowire Array Based Photodetectors

A large number of derivative phases in inorganic perovskites are reported with special structures and extraordinary performances in photoelectronic device applications. The reverse phase transition between derivative phases and perovskites usually induces recrystallization or forms mixed components. In this work, derivative phase‐induced growth of the CsPbBr₃ micro–nanowire (MW) array by utilizing phase transition of the 2D CsPb₂Br₅ phase is reported. Owing to its layered structure and phase transition, annealing of CsPb₂Br₅ at a temperature of 550 °C combined with solvent quenching leads to a templating effect to form a high‐quality CsBr MW array. Subsequent PbBr₂ deposition and the second annealing are employed to form aligned CsPbBr₃ MW arrays. Based on this method, a CsPbBr₃ MW array‐based photodetector is fabricated. The large grain size, less grain boundaries, and lower surface potential of the CsPbBr₃ MW array lead to high device performance with a responsivity of 7.66 A W^?1, a detectivity of ≈10¹² Jones, and long‐term operational stability over 1900 min.     

Piezoelectric Nanogenerator Based on In Situ Growth All-Inorganic CsPbBr3 Perovskite Nanocrystals in PVDF Fibers with Long-Term Stability

Inorganic lead halide perovskite has become an emerging material for modern photoelectric and electronic nanodevices due to its excellent optical and electronic properties. In view of its huge dielectric and electrical properties, inorganic CsPbBr₃ perovskite is introduced into the piezoelectric nanogenerator (PENG). Based on one-step electrospinning of solutions containing CsPbBr₃ precursors and polyvinylidene difluoride (PVDF), in situ growth of CsPbBr₃ nanocrystals in PVDF fibers (CsPbBr₃@PVDF composite fibers) with highly uniform size and spatial distribution are synthesized. The CsPbBr₃@PVDF composite fibers based PENG reveals an open-circuit voltage (V_oc) of 103 V and a density of short-circuit current (I_sc) of 170  µ A cm⁻², where the V_oc is comparable to the state-of-the-art hybrid composite piezoelectric nanogenerators (PENGs) and the density of I_sc is 4.86 times higher than that of lead halide perovskites counterpart ever reported. Moreover, CsPbBr₃@PVDF composite fibers based PENG exhibits fundamentally improved thermal/water/acid–base stabilities. This study suggests that the CsPbBr₃@PVDF composite fiber is a good candidate for fabricating high-performance PENGs, promising application potentials in mechanical energy harvesting and motion sensing technologies.     

Surfactant free hydrothermally derived ZnO nanowires,nanorods, microrods and their characterization

ZnO nanowires, nanorods and microrods have been prepared by an organic-free hydrothermal process using ZnSO₄ and NaOH/NH₄OH solutions. The powder X-ray diffraction (PXRD) patterns reveal that the ZnO nano/microrods are of hexagonal wurtzite structure. The Fourier transform infrared (FT-IR) spectrum of ZnO powder shows only one significant spectroscopic band at around 417 cm^?1 associated with the characteristic vibrational mode of Zn–O bonding. The thickness 75–300 nm for ZnO nanorods and 0.2–1.8 μm for microrods are identified from SEM/TEM images. UV–visible absorption spectra of ZnO nano/microrods show the blue shift. The UV band and green emission observed in photoluminescence (PL) spectra are due to free exciton emission and singly ionized oxygen vacancy in ZnO. Finally, the mechanism for organic-free hydrothermal synthesis of the ZnO nano/microrods is discussed.     

Surface Modification Strategy Synthesized CsPbX3 Perovskite Quantum Dots with Excellent Stability and Optical Properties in Water

The poor stability of CsPbX₃ (X = Cl, Br, I) perovskite quantum dots (PQDs) in polar solvents such as water, seriously hinders their practical application. Herein, 5-Bromovaleric acid (BVA) is used to replace oleic acid (OA), the most common surface ligand in CsPbX₃ PQDs synthesis. Under the synergic action of oleylamine (OLA), CsPbX₃ PQDs with high water stability can be synthesized directly in water. Because the carboxyl ligands provided by BVA, and the long chain amines provided by OLA formed hydrophobic shells on the surface of CsPbBr₃ PQDs, the obtained CsPbBr₃ PQDs still has high luminescence intensity and photoluminescence quantum yield after being dispersed in water for several days, and the luminescence peak is always maintained at 518 nm. In contrast, the luminescence intensity of CsPbBr₃ PQDs synthesized with OA and OLA is <1% of the initial intensity after only 30 min. CsPbCl₃ and CsPbI₃ PQDs synthesized directly in water by this method also show high water stability. In this study, for the first time the synthesis method of CsPbX₃ PQDs with high water stability using BVA/OLA as surface ligands is proposed, which provides an effective way to explore the synthesis of PQDs that can maintain stability in water.     

Surface Ligands Stabilized Lead Halide Perovskite Quantum Dot Photocatalyst for Visible Light‐Driven Hydrogen Generation

Solar hydrogen conversion represents a clean and economic approach to addressing global energy and environmental issues, for which efficient photocatalysts are heavily pursued. Lead halide perovskites are promising candidates for efficient phtocatalysts in solar hydrogen generation due to their attractive properties in light absorption, photogenerated charge transportation, and utilization. However, photocatalytic applications of lead halide perovskites are limited owing to their poor stability in the presence of water or other polar solvent environment. This work presents the rational control of surface ligands in achieving a good balance between stability and photocatalytic activity of CsPbBr₃ quantum dots (QDs). Detailed studies reveal that the deliberate surface ligands engineering is crucial for maximizing the photocatalytic activity of CsPbBr₃ QDs while maintaining good QD stability. A certain amount of surface ligands protect the CsPbBr₃ QDs from decomposition in moisture during the photocatalytic reaction while still enabling efficient charge transfer for photocatalytic reactions on the surface of QDs. The well‐controlled CsPbBr₃ photocatalyst shows efficient visible light‐driven H₂ generation with outstanding stability (≥160 h).     

Activation of Self-Trapped Emission in Stable Bismuth-Halide Perovskite by Suppressing Strong Exciton–Phonon Coupling

All-inorganic bismuth-halide perovskites are promising alternatives for lead halide perovskites due to their admirable chemical stability and optoelectronic properties; however, these materials deliver inferior photoluminescence (PL) properties, severely hindering their prospects in lighting applications. Here, a novel air-stable but non-emissive perovskite Rb₃BiCl₆ is synthesized, and the material is used as a prototype to uncover origin of the poor optical performance in bismuth-halide perovskite. It is found that the extremely strong exciton–phonon interactions with a large coupling constant up to 693 meV leads to the seriously nonradiative recombination, which, however, can be effectively suppressed to 347 meV by introducing Sb³⁺ ions. As a result, Sb³⁺-doped Rb₃BiCl₆ exhibits a stable yellow emission with unprecedented PL quantum yield up to 33.6% from self-trapped excitons. Systematic spectroscopic characterizations and theoretical calculations are carried out to unveil the intriguing photophysical mechanisms. This work reveals the effect of exciton–phonon interaction, that is often underemphasized, on a material's photophysical properties.     

Efficient and Stable Perovskite White Light-Emitting Diodes for Backlit Display

High-quality backlit display puts forward urgent demand for color-converting materials. Recently, metal halide perovskites (MHPs) with full spectral tunability, high photoluminescence quantum yields (PLQYs), and high color purity have found potential application in wide-color-gamut display. Regrettably, naked MHPs suffer from long-term instable issue and cannot pass harsh stability tests. Herein, amorphous-glass-protected green/red CsPbX₃ quantum dots (QDs) are prepared by elaborately optimizing glass structure, perovskite concentration, and in situ crystallization. PLQYs of green CsPbBr₃@glass and red CsPbBr_1.5I_1.5@glass reach 94% and 78%, respectively, which are the highest ones of CsPbX₃@glass composites reported so far and comparable to colloidal counterparts. Benefited from complete isolation of QDs from external environment by glass network, CsPbX₃@glass can endure harsh commercial standard aging tests of 85 °C/85%RH and blue-light-irradiation, which are applied to construct white light-emitting diodes (wLEDs) with high external quantum efficiency of 13.8% and ultra-high luminance of 500 000 cd m⁻². Accordingly, the perovskite wLED arrays-based backlit unit and a prototype display device are designed for the first time, showing more vivid and wide-color-gamut feature benefited from narrowband emissions of CsPbX₃ QDs. This work highlights practical application of CsPbX₃@glass composite as an efficient and stable light color converter in backlit display.     

Compositional and Dimensional Control of 2D and Quasi‐2D Lead Halide Perovskites in Water

Blue light emitting two dimensional (2D) and quasi‐2D layered halide perovskites (LHPs) are gaining attention in solid‐state lighting applications but their fragile stability in humid condition is one of the most pressing issues for their practical applications. Though water is much greener and cost effective, organic solvents must be used during synthesis as well as the device fabrication process for these LHPs due to their water‐sensitivity/instability and consequently, water‐stable blue‐light emitting 2D and quasi‐2D LHPs have not been documented yet. Here, water‐mediated facile and cost‐effective syntheses, characterizations, and optical properties of 16 organic–inorganic hybrid compounds are reported including 2D (A′)₂PbX₄ (A′ = butylammonium, X = Cl/Br/I) (8 compounds), 3D perovskites (4), and quasi‐2D (A′)_pA_x?1B_xX_3x+1 LHPs (A = methylammonium) (4) in water. Here, both composition and dimension of LHPs are tuned in water, which has never been explored yet. Furthermore, the dual emissive nature is observed in quasi‐2D perovskites, where the intensity of two photoluminescence (PL) peaks are governed by 2D and 3D inorganic layers. The Pb(OH)₂‐coated 2D and quasi‐2D perovskites are highly stable in water even after several months. In addition, single particle imaging is performed to correlate structural–optical property of these LHPs.