In Situ Fabrication of Halide Perovskite Nanocrystal-Embedded Polymer Composite Films with Enhanced Photoluminescence for Display Backlights

Ultrastable Quantum Dot Composite Films under Severe Environments

Semiconductor quantum dots (QDs) have attracted extensive attention because of their remarkable optical and electrical characteristics. However, the practical application of QDs and further the QD composite films have greatly been hindered mainly owing to their essential drawbacks of extreme unstability under oxygen and water environments. Herein, one simple method has been employed to enhance enormously the stability of Cd _xZn_{1- x}Se _yS_{1- y} QD composite films by a combination of Cd _xZn_{1- x}Se _yS_{1- y} QDs and poly(vinylidene) fluoride (PVDF), which is characteristic of closely arranged molecular chains and strong hydrogen bonds. There are many particular advantages in using QD/PVDF composite films such as easy processing, low cost, large-area fabrication, and especially extreme stability even in the boiling water for more than 240 min. By employing K₂SiF₆:Mn⁴⁺ as a red phosphor, a prototype white light-emitting diode (WLED) with color coordinates of (0.3307, 0.3387), T_c of 5568 K, and color gamut 112.1NTSC(1931)% at 20 mA has been fabricated, and there is little variation under different excitation currents, indicating that the QD/PVDF composite films fabricated by this simple blade-coating process make them ideal candidates for liquid-crystal display backlight utilization via assembling a WLED on a large scale owing to its ultrahigh stability under severe environments.

Perovskite-Initiated Photopolymerization for Singly Dispersed Luminescent Nanocomposites

Metal halide perovskites have demonstrated rich photophysics and remarkable potential in photovoltaic and electroluminescent devices. However, the photoactivity of perovskite semiconductors in chemical processes remains relatively unexplored. Here, a general approach toward the synthesis of luminescent perovskite-polymer nanocomposites is reported, whereby perovskite nanocrystals are used as photoinitiators in the polymerization of vinyl monomers. The white-light illumination of a perovskite-monomer mixture triggers a free-radical chain-growth polymerization process, giving rise to high molecular weight polymers of ≈200 kDa. The in situ growth of polymer chains from the perovskite crystal surface allows the formation of individually dispersed nanocrystal cores within an encapsulating polymer matrix, and leads to a significant threefold enhancement in photoluminescence quantum yield. This photoluminescence enhancement is attributed to the spatial separation of the perovskite nanocrystals and hence the deactivation of energy transfer to dark crystals. The resulting perovskite-polymer nanocomposites exhibit excellent stability against moisture and are shown to be useful as functional downconversion phosphor films for luminescent displays and lighting.

Toward Highly Luminescent and Stabilized Silica-Coated Perovskite Quantum Dots through Simply Mixing and Stirring under Room Temperature in Air

Methylammonium (MA) lead halide (MAPbX₃, X = Cl, Br, I) perovskite quantum dots (PQDs) are very sensitive to environment (moisture, oxygen, and temperature), suffering from poor stability. To improve the stability, we synthesized silica-coated PQDs (SPQDs) by an improved ligand-assisted reprecipitation method through simply mixing and stirring under room temperature in air without adding water and catalyst, the whole process took only a few seconds. The photoluminescence (PL) spectra of the SPQDs can be tuned continuously from 460 to 662 nm via adjusting the composition proportion of precursors. The highest PL quantum yields (PLQYs) of blue-, green-, and red-emissive SPQDs are 56, 95, and 70%, respectively. The SPQDs show remarkably improved environmental and thermal stability compared to the naked PQDs because of effective barrier created by the coated silica between the core materials and the ambience. Furthermore, it is found that different light-emitting SPQDs can maintain their original PL properties after mixing of them and anion-exchange reactions have not happened. These attributes were then used to mix green- and yellow-emissive SPQDs with polystyrene (PS) to form color-converting layers for the fabrication of white light-emitting devices (WLEDs). The WLEDs exhibit excellent white light characteristics with CIE 1931 color coordinates of (0.31, 0.34) and color rendering index (CRI) of 85, demonstrating promising applications of SPQDs in lighting and displays.

Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 μJ cm^-2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.

Colloidal CsPbX3 (X = Cl, Br, I) Nanocrystals 2.0: Zwitterionic Capping Ligands for Improved Durability and Stability

Colloidal lead halide perovskite nanocrystals (NCs) have recently emerged as versatile photonic sources. Their processing and optoelectronic applications are hampered by the loss of colloidal stability and structural integrity due to the facile desorption of surface capping molecules during isolation and purification. To address this issue, herein, we propose a new ligand capping strategy utilizing common and inexpensive long-chain zwitterionic molecules such as 3-(N,N-dimethyloctadecylammonio)propanesulfonate, resulting in much improved chemical durability. In particular, this class of ligands allows for the isolation of clean NCs with high photoluminescence quantum yields (PL QYs) of above 90% after four rounds of precipitation/redispersion along with much higher overall reaction yields of uniform and colloidal dispersible NCs. Densely packed films of these NCs exhibit high PL QY values and effective charge transport. Consequently, they exhibit photoconductivity and low thresholds for amplified spontaneous emission of 2 μJ cm^-2 under femtosecond optical excitation and are suited for efficient light-emitting diodes.

Rb+ cations enable the change of luminescence properties in perovskite (RbxCs1-xPbBr3) quantum dots

All-inorganic metal halide perovskites of the formulation ABX₃ (where A is Cs⁺, B is commonly Pb²⁺, and X is a halide, X = Cl, Br, I) have been studied intensively for their unique properties. Most of the current studies focus on halogen exchange to modify the luminescence band gap. Herein we demonstrate a new avenue for changing the band gap of halide perovskites by designing mixed-monovalent cation perovskite-based colloidal quantum dot materials. We have synthesized monodisperse colloidal quantum dots of all-inorganic rubidium-cesium lead halide perovskites (APbBr₃, A = mixed monovalent cation systems Rb/Cs) using inexpensive commercial precursors. Through the compositional modulation, the band gap and emission spectra are readily tunable over the visible spectral range of 474-532 nm. The photoluminescence (PL) of Rb_xCs_1-xPbBr₃ nanocrystals is characterized with excellent (NTCS color standard) wide color gamut coverage, which is similar to the cesium lead halide perovskites (CsPbX₃, X = mixed halide systems Cl/Br), and narrow emission line-widths of 27-34 nm. Furthermore, simulated lattice models and band structures are used to explain the band gap variations.

Highly Stable and Luminescent Perovskite-Polymer Composites from a Convenient and Universal Strategy

Extensive attention has been received in recent years for perovskite-polymer composites because of their combination of properties from polymers and perovskites. In this work, a convenient and universal strategy is reported to prepare cesium lead bromide or organolead halide methylammonium bromide polymer composites. This technique integrates the formation of perovskite crystals and the polymer matrix in a one-pot reaction, avoiding the tedious separation and preparation of perovskites. The method is universal for most of the commercially available monomers and polymers, which has been verified in this report using poly(methyl methacrylate), poly(butyl methacrylate), and polystyrene. The physical properties of the varied polymers lead to different luminescent properties and stabilities of the composites. No organic solvent is required during the preparation, indicating a green technique for the composites. Additionally, the resulted perovskite-polymer composites are extraordinarily stable, maintaining their quantum yield for more than 1 month in air. On the basis of the above properties, a prototype of white light-emitting diodes was successfully constructed with feasible color characters and narrow bandwidths. Furthermore, large-area (dimension: 10 × 7 × 0.15 cm) perovskite-polymer plates are easily prepared via the one-pot strategy, showing that the technique is ready for possible large-area optical devices. This work provides an efficient technique toward various kinds of perovskite-polymer composites for both scientific research studies and future applications.

Flexible/curved backlight module with quantum-dots microstructure array for liquid crystal displays

We present a backlight module (BLM) employing a photoluminescent quantum-dot microstructure array for flexible/curved liquid crystal displays (LCDs). Differently sized quantum-dot (QD) BLMs were prepared based on the theoretical spectral model and microstructure fabrication process. A 27-inch curved prototype showed a wide color gamut of 122.79% under the National Television Systems Committee standard while achieving high brightness of over 4000 cd/m² and brightness/color uniformity of 85.21%/9.2 × 10^-3. An LCD monitor prototype equipped with the proposed BLM was also assembled and tested, which showed higher visual performance when compared with a common commercial monitor. This method produces QD BLMs without the need of additional optical elements, and has good compatibility with traditional processes.

Reversible transformation between CsPbBr3 and Cs4PbBr6 nanocrystals

We introduce both phase and morphology reversible transformation between CsPbBr₃ and Cs₄PbBr₆ nanocrystals where the cubic morphology of the former is preserved.

White perovskite based lighting devices

Hybrid organic–inorganic and all-inorganic metal halide perovskites have been one of the most intensively studied materials during the last few years.

Synthesis and characterization of Mn-doped CsPb(Cl/Br)3 perovskite nanocrystals with controllable dual-color emission

Colloidal Mn-doped CsPb(Cl/Br)₃ NCs were synthesized at different MnCl₂-to-PbBr₂ molar feed ratios or reaction temperatures to tune their color emission.

Perovskite Quantum Dots and Their Application in Light-Emitting Diodes

Perovskite quantum dots (PQDs) attract significant interest in recent years because of their unique optical properties, such as tunable wavelength, narrow emission, and high photoluminescence quantum efficiency (PLQY). Recent studies report new types of formamidinium (FA) PbBr₃ PQDs, PQDs with organic-inorganic mixed cations, divalent cation doped colloidal CsPb_1-x M_x Br₃ PQDs (M = Sn²⁺ , Cd²⁺ , Zn²⁺ , Mn²⁺ ) featuring partial cation exchange, and heterovalent cation doped into PQDs (Bi³⁺ ). These PQD analogs open new possibilities for optoelectronic devices. For commercial applications in lighting and backlight displays, stability of PQDs requires further improvement to prevent their degradation by temperature, oxygen, moisture, and light. Oxygen and moisture-facilitated ion migration may easily etch unstable PQDs. Easy ion migration may result in crystal growth, which lowers PLQY of PQDs. Surface coating and treatment are important procedures for overcoming such factors. In this study, new types of PQDs and a strategy of improving their stabilities are introduced. Finally, this paper discusses future applications of PQDs in light-emitting diodes.

High Performance Metal Halide Perovskite Light-Emitting Diode: From Material Design to Device Optimization

Metal halide perovskites have drawn significant interest in the past decade. Superior optoelectronic properties, such as a narrow bandwidth, precise and facile tunable luminance over the entire visible spectrum, and high photoluminescence quantum yield of up to ≈100%, render metal halide perovskites suitable for next-generation high-definition displays and healthy lighting systems. The external quantum efficiency of perovskite light-emitting diodes (LEDs) increases from 0.1 to 11.7% in three years; however, the energy conversion efficiency and the long-term stability of perovskite LEDs are inadequate for practical application. Strategies to optimize the emitting layer and the device structure, with respect to material design, synthesis, surface passivation, and device optimization, are reviewed and highlighted. The long-term stability of perovskite LEDs is evaluated as well. Meanwhile, several challenges and prospects for future development of perovskite materials and LEDs are identified.

Influence of the Grain Size on the Properties of CH3NH3PbI3 Thin Films

Hybrid perovskites have already shown a huge success as an absorber in solar cells, resulting in the skyrocketing rise in the power conversion efficiency to more than η = 22%. Recently, it has been established that the crystal quality is one of the most important parameters to obtain devices with high efficiencies. However, the influence of the crystal quality on the material properties is not fully understood. Here, the influence of the morphology on electronic properties of CH₃NH₃PbI₃ thin films is investigated. Postannealing was used to vary the average grain size continuously from ≈150 to ≈1000 nm. Secondary grain growth is thermally activated with an activation energy of E_a = 0.16 eV. The increase in the grain size leads to an enhancement of the photoluminescence, indicating an improvement in the material quality. According to surface photovoltage measurements, the charge-carrier transport length exhibits a linear increase with increasing grain size. The charge-carrier diffusion length is limited by grain boundaries. Moreover, an improved morphology leads to a drastic increase in power conversion efficiency of the devices.

Growth mechanism of strongly emitting CH3NH3PbBr3 perovskite nanocrystals with a tunable bandgap

Metal halide perovskite nanocrystals are promising materials for a diverse range of applications, such as light-emitting devices and photodetectors. We demonstrate the bandgap tunability of strongly emitting CH₃NH₃PbBr₃ nanocrystals synthesized at both room and elevated (60 °C) temperature through the variation of the precursor and ligand concentrations. We discuss in detail the role of two ligands, oleylamine and oleic acid, in terms of the coordination of the lead precursors and the nanocrystal surface. The growth mechanism of nanocrystals is elucidated by combining the experimental results with the principles of nucleation/growth models. The proposed formation mechanism of perovskite nanocrystals will be helpful for further studies in this field and can be used as a guide to improve the synthetic methods in the future.The development of perovskite nanocrystals is limited by poor mechanistic understanding of their growth. Here, the authors systematically study the ligand-assisted reprecipitation synthesis of CH₃NH₃PbBr₃ nanocrystals, revealing the effect of precursor and ligand concentrations on bandgap tunability.

Highly luminescent, stable, transparent and flexible perovskite quantum dot gels towards light-emitting diodes

By controlling the hydrolysis of alkoxysilanes, highly luminescent, transparent and flexible perovskite quantum dot (QD) gels were synthesized. The gels could maintain the structure without shrinking and exhibited excellent stability comparing to the QDs in solution. This in situ fabrication can be easily scaled up for large-area/volume gels. The gels integrated the merits of the polymer matrices to avoid the non-uniformity of light output, making it convenient for practical LED applications. Monochrome and white LEDs were fabricated using these QD gels; the LEDs exhibited broader color gamut, demonstrating better property in the backlight display application.

Lead Halide Perovskite Nanocrystals in the Research Spotlight: Stability and Defect Tolerance

This Perspective outlines basic structural and optical properties of lead halide perovskite colloidal nanocrystals, highlighting differences and similarities between them and conventional II-VI and III-V semiconductor quantum dots. A detailed insight into two important issues inherent to lead halide perovskite nanocrystals then follows, namely, the advantages of defect tolerance and the necessity to improve their stability in environmental conditions. The defect tolerance of lead halide perovskites offers an impetus to search for similar attributes in other related heavy metal-free compounds. We discuss the origins of the significantly blue-shifted emission from CsPbBr₃ nanocrystals and the synthetic strategies toward fabrication of stable perovskite nanocrystal materials with emission in the red and infrared parts of the optical spectrum, which are related to fabrication of mixed cation compounds guided by Goldschmidt tolerance factor considerations. We conclude with the view on perspectives of use of the colloidal perovskite nanocrystals for applications in backlighting of liquid-crystal TV displays.

Going beyond the limit of an LCD's color gamut

In this study, we analyze how a backlight's peak wavelength, full-width at half-maximum (FWHM), and color filters affect the color gamut of a liquid crystal display (LCD) device and establish a theoretical limit, even if the FWHM approaches 1 nm. To overcome this limit, we propose a new backlight system incorporating a functional reflective polarizer and a patterned half-wave plate to decouple the polarization states of the blue light and the green/red lights. As a result, the crosstalk between three primary colors is greatly suppressed, and the color gamut is significantly widened. In the experiment, we prepare a white-light source using a blue light-emitting diode (LED) to pump green perovskite polymer film and red quantum dots and demonstrate an exceedingly large color gamut (95.8% Rec. 2020 in Commission internationale de l'éclairage (CIE) 1931 color space and 97.3% Rec. 2020 in CIE 1976 color space) with commercial high-efficiency color filters. These results are beyond the color gamut limit achievable by a conventional LCD. Our design works equally well for other light sources, such as a 2-phosphor-converted white LED.

Photoaligned Nanorod Enhancement Films with Polarized Emission for Liquid-Crystal-Display Applications

Semiconductor nanorods (NR) emit polarized light, which is expected to bring manifold benefits, in terms of brightness and color enhancement, for modern liquid-crystal displays (LCD). In this regard, photoaligned nanorod enhancement films (NREF) for color and polarization conversion for LCD backlights are introduced here. The photoinduced anchoring forces, by the photoalignment layer, stimulate well-ordered self-assembly of NR in the thin polymer films. Green and red emitting NR with a quantum yield of ≈80% are aligned unidirectionally and in-plane, showing a polarization ratio of >7:1 and a degree of polarization of >0.81. The photoalignment technique facilitates the fabrication of mixed and multiple stacked NREF for LCDs, which improves the color gamut and polarization efficiency, and is thus expected to increase the optical efficiency of conventional LCDs by ≈60%.

Chemically Addressable Perovskite Nanocrystals for Light-Emitting Applications

Whereas organic-inorganic hybrid perovskite nanocrystals (PNCs) have remarkable potential in the development of optoelectronic materials, their relatively poor chemical and colloidal stability undermines their performance in optoelectronic devices. Herein, this issue is addressed by passivating PNCs with a class of chemically addressable ligands. The robust ligands effectively protect the PNC surfaces, enhance PNC solution processability, and can be chemically addressed by thermally induced crosslinking or radical-induced polymerization. This thin polymer shield further enhances the photoluminescence quantum yields by removing surface trap states. Crosslinked methylammonium lead bromide (MAPbBr₃ ) PNCs are applied as active materials to build light-emitting diodes that have low turn-on voltages and achieve a record luminance of over 7000 cd m^-2 , around threefold better than previous reported MA-based PNC devices. These results indicate the great potential of this ligand passivation approach for long lifespan, highly efficient PNC light emitters.

Perovskite quantum dots encapsulated in electrospun fiber membranes as multifunctional supersensitive sensors for biomolecules, metal ions and pH

CsPbBr₃ perovskite quantum dots (CPBQDs) have exhibited excellent optical properties, which implies their potential as an appealing candidate for fluorescence resonance energy transfer (FRET) based detection. In this work, in order to enhance the subsurface concentration of CPBQDs, which is important for the efficiency of FRET detection, a nanoscale polymethyl methacrylate (PMMA) fiber membrane (d≈ 400 nm) encapsulated with CPBQDs (CPBQDs/PMMA FM) is fabricated using an electrospinning method. The CPBQD/PMMA FM possesses comparable optical properties to CPBQDs, high quantum yields (88%) and a narrow half-peak width (∼14 nm). The sensing of trypsin is realized via the cleavage of peptide CF6 (Cys-Pro-Arg-Gly-R6G) and an extremely low detection limit of 0.1 μg mL^-1 has been reached. Besides, owing to the high efficiency FRET process between the CPBQD/PMMA FM and cyclam-Cu²⁺, an unprecedented detection limit of Cu²⁺ has been pushed to 10^-15 M. Furthermore, the pH value can be confirmed by the membrane in 10 ppb hydrazide R6G ethanol solution. The excellent optical characteristics of CPBQDs, high CPBQD subsurface concentration of the CPBQD/PMMA FM and robust durability of the PMMA coating all contribute to the outstanding sensitivity and stable detection performance of the CPBQD/PMMA FM.

Chemically Tailoring the Dopant Emission in Manganese-Doped CsPbCl3 Perovskite Nanocrystals

Doping in perovskite nanocrystals adopts different mechanistic approach in comparison to widely established doping in chalcogenide quantum dots. The fast formation of perovskites makes the dopant insertions more competitive and challenging. Introducing alkylamine hydrochloride (RNH₃ Cl) as a promoting reagent, precise controlled doping of Mn^II in CsPbCl₃ perovskite nanocrystals is reported. Simply, by changing the amount of RNH₃ Cl, the Mn incorporation and subsequent tuning in the excitonic as well as Mn d-d emission intensities are tailored. Investigations suggested that RNH₃ Cl acted as the chlorinating source, controlled the size, and also helps in increasing the number of particles. This provided more opportunity for Mn ions to take part in reaction and occupied the appropriate lattice positions. Carrying out several reactions with varying reaction parameters, the doping conditions are optimized and the role of the promoting reagent for both doped and undoped systems are compared.

Highly Luminescent and Ultrastable CsPbBr3 Perovskite Quantum Dots Incorporated into a Silica/Alumina Monolith

We successfully prepared QDs incorporated into a silica/alumina monolith (QDs-SAM) by a simple sol-gel reaction of an Al-Si single precursor with CsPbBr₃ QDs blended in toluene solution, without adding water and catalyst. The resultant transparent monolith exhibits high photoluminescence quantum yields (PLQY) up to 90 %, and good photostability under strong illumination of blue light for 300 h. We show that the preliminary ligand exchange of didodecyl dimethyl ammonium bromide (DDAB) was very important to protect CsPbBr₃ QDs from surface damages during the sol-gel reaction, which not only allowed us to maintain the original optical properties of CsPbBr₃ QDs but also prevented the aggregation of QDs and made the monolith transparent. The CsPbBr₃ QDs-SAM in powder form was easily mixed into the resins and applied as color-converting layer with curing on blue light-emitting diodes (LED). The material showed a high luminous efficacy of 80 lm W^-1 and a narrow emission with a full width at half maximum (FWHM) of 25 nm.

Synthesis and Stabilization of Colloidal Perovskite Nanocrystals by Multidentate Polymer Micelles

Lead halide perovskites have emerged as low-cost, high-performance optical and optoelectronic materials, however, their material stability has been a limiting factor for broad applications. Here, we demonstrate stable core-shell colloidal perovskite nanocrystals using a novel, facile and low-cost copolymer templated synthesis approach. The block copolymer serves as a confined nanoreactor during perovskite crystallization and passivates the perovskite surface by forming a multidentate capping shell, thus significantly improving its photostability in polar solvents. Meanwhile, the polymer nanoshell provides an additional layer for further surface modifications, paving the way to functional nanodevices that can be self-assembled or lithographically defined.

Ultra-bright and highly efficient inorganic based perovskite light-emitting diodes

Inorganic perovskites such as CsPbX₃ (X=Cl, Br, I) have attracted attention due to their excellent thermal stability and high photoluminescence quantum efficiency. However, the electroluminescence quantum efficiency of their light-emitting diodes was <1%. We posited that this low efficiency was a result of high leakage current caused by poor perovskite morphology, high non-radiative recombination at interfaces and perovskite grain boundaries, and also charge injection imbalance. Here, we incorporated a small amount of methylammonium organic cation into the CsPbBr₃ lattice and by depositing a hydrophilic and insulating polyvinyl pyrrolidine polymer atop the ZnO electron-injection layer to overcome these issues. As a result, we obtained light-emitting diodes exhibiting a high brightness of 91,000 cd m⁻² and a high external quantum efficiency of 10.4% using a mixed-cation perovskite Cs_0.87MA_0.13PbBr₃ as the emitting layer. To the best of our knowledge, this is the brightest and most-efficient green perovskite light-emitting diodes reported to date.

Hybrid organic-inorganic perovskites are garnering attention for light emitting diode (LED) applications. Employing a thin hydrophilic insulating polymer, Zhang et al. report LEDs exhibiting a brightness of 91,000 cd m⁻² and external quantum efficiency of 10.4% using a mixed-cation perovskite.

Hybrid downconverters with green perovskite-polymer composite films for wide color gamut displays

We propose to use a hybrid downconverter system comprising low-cost green perovskite-polymer composite films for liquid crystal display (LCD) backlight unit (BLU) to realize wide color gamut. Recently, ultrastable, highly luminescent CH₃NH₃PbBr₃ (MAPbBr₃) organic-inorganic perovskite-polymer composite films have been developed. These films exhibit outstanding color quality with a full-width-at-half-maximum (FWHM) of only 18 nm and a peak wavelength of 530 nm, which makes them promising candidates as green downconverters. Two configurations to hybridize these green films with state-of-the-art red emitting downconverters, including CdSe-based quantum dots (QDs) and narrow peak phosphors, are proposed. Color and efficiency analyses indicate that the hybridization of green perovskite-polymer films with red K₂SiF₆:Mn⁴⁺ (KSF) phosphor could lead to wide color gamut coverage of nearly 90% Rec. 2020 and high total light efficiency (TLE) of around 20 lm/W while maintaining low cost.

In Situ Preparation of Metal Halide Perovskite Nanocrystal Thin Films for Improved Light-Emitting Devices

Hybrid organic-inorganic halide perovskite semiconductors are attractive candidates for optoelectronic applications, such as photovoltaics, light-emitting diodes, and lasers. Perovskite nanocrystals are of particular interest, where electrons and holes can be confined spatially, promoting radiative recombination. However, nanocrystalline films based on traditional colloidal nanocrystal synthesis strategies suffer from the use of long insulating ligands, low colloidal nanocrystal concentration, and significant aggregation during film formation. Here, we demonstrate a facile method for preparing perovskite nanocrystal films in situ and that the electroluminescence of light-emitting devices can be enhanced up to 40-fold through this nanocrystal film formation strategy. Briefly, the method involves the use of bulky organoammonium halides as additives to confine crystal growth of perovskites during film formation, achieving CH₃NH₃PbI₃ and CH₃NH₃PbBr₃ perovskite nanocrystals with an average crystal size of 5.4 ± 0.8 nm and 6.4 ± 1.3 nm, respectively, as confirmed through transmission electron microscopy measurements. Additive-confined perovskite nanocrystals show significantly improved photoluminescence quantum yield and decay lifetime. Finally, we demonstrate highly efficient CH₃NH₃PbI₃ red/near-infrared LEDs and CH₃NH₃PbBr₃ green LEDs based on this strategy, achieving an external quantum efficiency of 7.9% and 7.0%, respectively, which represent a 40-fold and 23-fold improvement over control devices fabricated without the additives.

Thermal degradation of luminescence in inorganic perovskite CsPbBr3nanocrystals

The PL degradation of annealed CsPbBr₃NCs is related to both the formation of surface defects and growth of NCs.

Alkylthiol-enabled Se powder dissolving for phosphine-free synthesis of highly emissive, large-sized and spherical Mn-doped ZnSeS nanocrystals

The enhanced dissolution of Se without organo-phosphines is a key issue in the synthesis of oil-soluble selenide nanocrystals.

Ultrastable, Highly Luminescent Organic-Inorganic Perovskite-Polymer Composite Films

A simple yet general swelling-deswelling microencapsulation strategy has been developed to achieve well dispersed and intimately passivated crystalline organic-inorganic perovskites nanoparticles within polymer matrixes and results in a series of highly luminescent CH₃ NH₃ PbBr₃ (MAPbBr₃ )-polymer composite films with unprecedented water and thermal stabilities and superior color purity.