The Role of Metal Halide Perovskites in Next-Generation Lighting Devices

Mechanochemistry for Organic and Inorganic Synthesis

In recent years, mechanochemistry has become an innovative and sustainable alternative to traditional solvent-based synthesis. Mechanochemistry rapidly expanded across a wide range of chemistry fields, including diverse organic compounds and active pharmaceutical ingredients, coordination compounds, organometallic complexes, main group frameworks, and technologically relevant materials. This Review aims to highlight recent advancements and accomplishments in mechanochemistry, underscoring its potential as a viable and eco-friendly alternative to conventional solution-based methods in the field of synthetic chemistry.

Exploring Epitaxial Structures for Electrically Pumped Perovskite Lasers: A Study of CsPb(Br,I)3 Based on the Ab Initio Bethe-Salpeter Equation

Halide perovskites are widely used as components of electronic and optoelectronic devices such as solar cells, light-emitting diodes (LEDs), optically pumped lasers, field-effect transistors, photodetectors, and γ-detectors. Despite this wide range of applications, the construction of an electrically pumped perovskite laser remains challenging. In this paper, we numerically justify that mixing two perovskite compounds with different halide elements can lead to optical properties suitable for electrical pumping. As a reference, the chosen model material was CsPbBr3, whose performance as a part of lasers has been widely recognised, with some Br atoms substituted by I at specific sites. In particular, a strong enhancement of the low-energy absorption peaks has been obtained using the ab initio Bethe-Salpeter equation. Based on these results, we propose specific architectures of ordered doping that could be realised by epitaxial growth. Efficient light emission from the bottom of the conduction band is expected.

Investigation on broadband emission of two-dimensional melamine lead iodide perovskite (2D-C3H8N6PbI4): An experimental and theoretical approach

Novel two-dimensional melamine lead iodide perovskite (2D-C3H8N6PbI4) is synthesized to investigate its crystallinity, optical band gap and broadband emission properties and to make comparisons with 2D-C3H8N6PbCl4/2D-C3H8N6PbBr4 perovskites. Both experimental and density functional theory (DFT) interrogations on 2D-C3H8N6PbX4 (X = Cl, Br and I) are conducted. The crystal structure, morphology and percentile of Pb and halide elements are confirmed using scanning electron microscope (SEM), and energy dispersive spectrum (EDS), powder/single crystal X-ray diffraction (PXRD/SXRD), DFT and X-ray crystallography simulations. The optical band gaps of 2D-C3H8N6PbX4 perovskites are determined from the Tauc plot fitting of absorbance and DFT studies. Distinct broadband emission of 2D-C3H8N6PbX4 perovskites between 300 and 800 nm is observed, which can be fitted with multiple Gaussian distributions. The fittings of broad PL spectra from 2D-C3H8N6PbCl4/2D-C3H8N6PbBr4 perovskites confirm the involvement of both Dexter energy transfer from melamine cation and self-trapped excitons (STEs). However, the broadband emission of 2D-C3H8N6PbI4 is attributed only to the Dexter energy transfer from melamine cation and the absence of STEs is attributed to the larger lattice deformation of 2D-C3H8N6PbI4. Moreover, the involvement of spin-orbit coupling (SOC) in the energy transfer is clarified to attest that the broadband emission of 2D-C3H8N6PbI4 is distinct among its halide family.

Lead-free 2D MASnBr3 and Ruddlesden-Popper BA2MASn2Br7 as light harvesting materials

We have explored the structural, electronic, charge transport, and optical properties of lead-free 2D hybrid halide perovskites, MASnBr₃ and Ruddlesden-Popper perovskites, BAMASn₂Br₇ monolayers. Under density functional theory (DFT) calculation, we applied mechanical strain, i.e., tensile and compressive strain up to 10% in both cases. The mechanical strain engineering technique is useful for a tuned bandgap of 2D MASnBr₃ and 2D BAMASn₂Br₇. The calculated carrier mobility for the electron is 404 cm² V^-1 s^-1 and for the hole is up to 800 cm² V^-1 s^-1 for MASnBr₃. For BAMASn₂Br₇ the highest carrier mobility is up to 557 cm² V^-1 s^-1 for electrons and up to 779 cm² V^-1 s^-1 for the hole, which is 14% and 24% higher than the reported lead-iodide based perovskites, respectively. The calculated solar cell efficiency of 2D MASnBr₃ is 23.46%, which is 18% higher than the reported lead-based perovskites. Furthermore, the optical activity of the 2D MASnBr₃ and 2D BAMASn₂Br₇ shows a high static dielectric constant of 2.48 and 2.14, respectively. This is useful to show nanodevice performance. Also, 2D MASNBr₃ shows a high absorption coefficient of 15.25 × 10⁵ cm^-1 and 2D BAMASn₂Br₇ shows an absorption coefficient of up to 13.38 × 10⁵ cm^-1. Therefore our theoretical results suggest that the systems are under mechanical strain engineering. This is convenient for experimentalists to improve the performance of the 2D perovskites. The study supports these materials as good candidates for photovoltaic and optoelectronic device applications.

Determination of the optical constants of ligand-free organic lead halide perovskite quantum dots

Precise knowledge of the optical constants of perovskite lead halide quantum dots (QDs) is required to both understand their interaction with light and to rationally design and optimize the devices based on them. However, their determination from colloidal nanocrystal suspensions, or films made out of them, remains elusive, as a result of the difficulty in disentangling the optical constants of the organic capping ligands and those of the semiconductor itself. In this work, we extract the refractive index and extinction coefficient of ligand-free methylammonium lead iodide (MAPbI₃) and bromide (MAPbBr₃) nanocrystals. In order to prevent the use of organic ligands in the preparation, we follow a scaffold assisted synthetic procedure, which yields a composite film of high optical quality that can be independently and precisely characterized and modelled. In this way, the contribution of the guest nanocrystals can be successfully discriminated from that of the host matrix. Using a Kramers-Kronig consistent dispersion model along with an effective medium approximation, it is possible to derive the optical constants of the QDs by fitting the spectral dependence of light transmitted and reflected at different angles and polarizations. Our results indicate a strong dependence of the optical constants on the QD size. Small nanocrystals show remarkably large values of the extinction coefficient compared to their bulk counterparts. This analysis opens the door to the rigorous modelling of solar cells and light-emitting diodes with active layers based on perovskite QDs.

Anion-Dependent Polarization and Piezoelectric Power Generation in Hybrid Halide MAPbX3 (X = I, Br, and Cl) Thin Films with Out-of-Plane Structural Adjustments

Anion-dependent differences in the electromechanical energy harvesting capability of perovskite halides have not been experimentally demonstrated thus far. Herein, anion-dependent piezoelectricity and bending-driven power generation in high-quality methylammonium lead halide MAPbX₃ (X = I, Br, and Cl) thin films are explored; additionally, anisotropic in situ strain is imposed to improve energy harvesting under tensile bending. After applying the maximum in situ strain of -0.73% for all the halide thin films, the MAPbI₃ thin-film harvester exhibited a peak voltage/current of ≈23.1 V/≈1703 nA as the best values, whereas MAPbBr₃ and MAPbCl₃ demonstrated ≈5.6 V/≈176 nA and ≈3.3 V/≈141 nA, respectively, under identical bending conditions. Apart from apparent ferroelectricity of tetragonal MAPbI₃ , origin of the piezoelectricity in both cubic MAPbBr₃ and MAPbCl₃ is explored as being related to organic-inorganic hydrogen bonding, lattice distortion, and ionic migration, with experimental supports of effective piezoelectric coefficient and grain boundary potential. Conclusively, piezoelectricity of the cubic halides is assumed to be due to their soft polarity modes and relatively low elastic modulus with vacancies contributing to space-charge polarization. In the case of ferroelectric MAPbI₃ , the distortion of PbI₆ octahedra and atomic displacement within each octahedron are quantitatively estimated.

Modulation of the carrier balance of lead-halide perovskite nanocrystals by polyelectrolyte hole transport layers for near-infrared light-emitting diodes

An alternative material, methylamine (MA)-doped poly[3-(4-carboxymethyl)thiophene-2,5-diyl] (P3CT) as hole transport layer (HTL) was investigated for efficient solution-processed near-infrared perovskite light-emitting diodes (NIR PeLEDs). The best NIR PeLEDs performance was achieved with an optimized composition ratio of the MA-doped P3CT (1:1) due to the balance of the electron and hole carrier in the active layer. The charge-balanced NIR PeLEDs exhibit the highest radiance of 858.37 W sr⁻¹ m⁻², a low turn-on voltage of 1.82 V, and an external quantum efficiency of 7.44%. Our findings show that using P3CT as an alternative HTL has the potential to significantly improve PeLED performance, allowing it to play a role in the development of practical applications in high-power NIR LEDs.

PVDF-directed synthesis, stability and anion exchange of cesium lead bromide nanocrystals

Photoluminescent perovskite nanocrystals are mostly used along with base materials such as polymers for material processing and large-scale production purpose. However, the role of polymer in crystal structure engineering and thereby dictating the emission properties of lead halide perovskite nanocrystals is poorly understood. First, we have developed a polymer-directed antisolvent method for synthesis of halide perovskite crystals at room temperature. The thermodynamic stabilities of crystals drive the formation of perovskite composite crystal of orthorhombic Cs4PbBr6 and monoclinic CsPbBr3. Surprisingly, hydrophobic polyvinylidene fluoride (PVDF) can reduce the size of perovskite crystals to nano dimensions even at room temperature. On the other hand, perovskite nanocrystals, CsPbBr3 synthesized by modified hot-injection method undergo rapid encapsulation in PVDF matrices. The size of the encapsulated nanocrystal in PVDF matrices ranges in 88 ± 32 nm. Three types of radiative recombination are predominantly operative in nanocrystals-doped polymer- surface defect caused radiative recombination (0.6 - 3 ns), exciton recombination (3 - 15 ns), and shallow trap assisted recombination (10 - 50 ns). The interface created at nanocrystal and polymer plays a decisive role in populating the shallow trap states in perovskite-polymer nanocomposite. These nanocrystals have been shown to undergo fast halide exchange in aqueous hydroiodic acid solution and possess remarkable enhancement of water-/photo-stability. This research would pave way for their greater use in hydrogen production and light-emitting devices.

White light emission from lead-free mixed-cation doped Cs2SnCl6 nanocrystals

We have designed a synthesis procedure to obtain Cs₂SnCl₆ nanocrystals (NCs) doped with metal ion(s) to emit visible light. Cs₂SnCl₆ NCs doped with Bi³⁺, Te⁴⁺ and Sb³⁺ ions emitted blue, yellow and red light, respectively. In addition, NCs simultaneously doped with Bi³⁺ and Te⁴⁺ ions were synthesized in a single run. Combination of both dopant ions together gives rise to the white emission. The photoluminescence quantum yields of the blue, yellow and white emissions are up to 26.5, 28, and 16.6%, respectively under excitation at 350, 390, and 370 nm. Pure white-light emission with CIE chromaticity coordinates of (0.32, 0.33) and (0.32, 0.32) at 340 and 370 nm excitation wavelength, respectively, was obtained. The as-prepared NCs were found to demonstrate a long-time stability, resistance to humidity, and an ability to be well-dispersed in polar solvents without property degradation due to their hydrophilicity, which could be of significant interest for wide application purposes.

Structural and compositional properties of 2D CH3NH3PbI3 hybrid halide perovskite: a DFT study

Two-dimensional (2D) hybrid halide perovskites have been scrutinized as candidate materials for solar cells because of their tunable structural and compositional properties. Results based on density functional theory demonstrate its thickness-dependent stability. We have observed that the bandgap decreases from the mono- to quad-layer because of the transformation from 2D towards 3D. Due to the transformation, the carrier mobility is lowered with the corresponding smaller effective mass. On the other hand, the multilayer structures have good optical properties with an absorption coefficient of about 10⁵ cm⁻¹. The calculated absorption spectra lie between 248 nm and 496 nm, leading to optical activity of the 2D multilayer CH₃NH₃PbI₃ systems in the visible and ultraviolet regions. The strength of the optical absorption increases with an increase in thickness. Overall results from this theoretical study suggest that this 2D multilayer CH₃NH₃PbI₃ is a good candidate for photovoltaic and optoelectronic device applications.

We have studied 2D CH₃NH₃PbI₃ and its multilayer halide perovskites. These systems have a high formation energy. The optical properties absorption spectra lie between 248 nm to 496 nm with an absorption coefficient of about 10⁵ cm⁻¹.

Synthesis and Optical Properties of Mn2+-Doped Amino Lead Halide Molecular Clusters Assisted by Chloride Ion

Mn²⁺-doped amino lead halide molecular clusters (MCs) are synthesized using amine (e.g., n-octylamine, or butylamine) as passivating ligand and MnX₂ (X = Cl or Br) as the Mn²⁺ doping source at room temperature. Their optical properties are investigated with UV-visible absorption, photoluminescence (PL), and PL excitation spectroscopy. The Mn²⁺ precursor plays a vital role in the synthesis of Mn²⁺-doped MCs. MnCl₂ seems to facilitate the incorporation of Mn. The MnCl₂ doping causes electronic absorption blue shift and leads to a spin-forbidden ⁴T₁ → ⁶A₁ Mn d-electron emission. With the help of time-resolved PL, Fourier transform infrared, and electron paramagnetic resonance results, a model is proposed to explain the formation mechanism. We suggest that Mn²⁺ doping replaces Pb²⁺ is assisted by Cl^- ions that replace Br^- ions. This study demonstrates the possibility of doping MCs and has important implications in gaining new fundamental insight into the growth mechanisms of perovskite nanostructures.

Zinc (II) and AIEgens: The "Clip Approach" for a Novel Fluorophore Family. A Review

Aggregation-induced emission (AIE) compounds display a photophysical phenomenon in which the aggregate state exhibits stronger emission than the isolated units. The common term of "AIEgens" was coined to describe compounds undergoing the AIE effect. Due to the recent interest in AIEgens, the search for novel hybrid organic-inorganic compounds with unique luminescence properties in the aggregate phase is a relevant goal. In this perspective, the abundant, inexpensive, and nontoxic d10 zinc cation offers unique opportunities for building AIE active fluorophores, sensing probes, and bioimaging tools. Considering the novelty of the topic, relevant examples collected in the last 5 years (2016-2021) through scientific production can be considered fully representative of the state-of-the-art. Starting from the simple phenomenological approach and considering different typological and chemical units and structures, we focused on zinc-based AIEgens offering synthetic novelty, research completeness, and relevant applications. A special section was devoted to Zn(II)-based AIEgens for living cell imaging as the novel technological frontier in biology and medicine.

Local Morphology Effects on the Photoluminescence Properties of Thin CsPbBr3 Nanocrystal Films

Lead halide perovskites are emerging as extremely interesting active materials for a wide variety of optoelectronic and photonic devices. A deep understanding of their photophysics is thus fundamental in order to properly understand the origins of the materials active properties and to provide strategies for improving them. In this work, we exploit the local morphological variations in a drop-cast thin CsPbBr3 nanocrystal film to show that the aggregation of NCs has strong effects on the peak wavelengths of PL spectra, the linewidth, and the intensity of dependence on temperature. An analysis based on models that are frequently used in the literature led to completely different conclusions about the intrinsic NC emission properties extracted from spectra measured in points with different contribution of the PL from the aggregates. Our results demonstrate that extreme care has to be used in order to correctly correlate the spectral PL features with the intrinsic emission properties of lead halide perovskite NC films.

Toward Engineering Intrinsic Line Widths and Line Broadening in Perovskite Nanoplatelets

Perovskite nanoplatelets possess extremely narrow absorption and emission line widths, which are crucial characteristics for many optical applications. However, their underlying intrinsic and extrinsic line-broadening mechanisms are poorly understood. Here, we apply multidimensional coherent spectroscopy to determine the homogeneous line broadening of colloidal perovskite nanoplatelet ensembles. We demonstrate a dependence of not only their intrinsic line widths but also of various broadening mechanisms on platelet geometry. We find that decreasing nanoplatelet thickness by a single monolayer results in a 2-fold reduction of the inhomogeneous line width and a 3-fold reduction of the intrinsic homogeneous line width to the sub-millielectronvolts regime. In addition, our measurements suggest homogeneously broadened exciton resonances in two-layer (but not necessarily three-layer) nanoplatelets at room-temperature.

Data-driven enhancement of cubic phase stability in mixed-cation perovskites

Mixing cations has been a successful strategy in perovskite synthesis by solution-processing, delivering improvements in the thermodynamic stability as well as in the lattice parameter control. Unfortunately, the relation between a given cation mixture and the associated structural deformation is not well-established, a fact that hinders an adequate identification of the optimum chemical compositions. Such difficulty arises since local distortion and microscopic disorder influence structural stability and also determine phase segregation. Hence, the search for an optimum composition is currently based on experimental trial and error, a tedious and high-cost process. Here, we report on a machine-learning-reinforced cubic-phase-perovskite stability predictor that has been constructed over an extensive dataset of first-principles calculations. Such a predictor allows us to determine the cubic phase stability at a given cation mixture regardless of the various cations’ pair and concentration, even assessing very dilute concentrations, a notoriously challenging task for first-principles calculations. In particular, we construct machine learning models, predicting multiple target quantities such as the enthalpy of mixing and various octahedral distortions. It is then the combination of these targets that guide the laboratory synthesis. Our theoretical analysis is also validated by the experimental synthesis and characterization of methylammonium–dimethylammonium-mixed perovskite thin films, demonstrating the ability of the stability predictor to drive the chemical design of this class of materials.

Investigation of the exciton relaxation processes in poly(9,9-dioctylfluorene-co-benzothiadiazole):CsPbI1.5Br1.5 nanocrystal hybrid polymer–perovskite nanocrystal blend

The combination of lead halide perovskite nanocrystals and conjugated polymer in a blend film opens the way to the realization of hybrid active layers with widely tunable optical and electrical properties. However, the interaction between the polymeric and the perovskite component of the blends is mainly unexplored to date. In this work we perform temperature-dependent photoluminescence and time resolved photoluminescence measurements in order to deeply investigate the photophysics of a poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT):CsPbI_1.5Br_1.5 nanocrystal hybrid film. Our results suggest that the primary interaction channel is charge transfer, both from F8BT to the NCs and from the NCs to F8BT, while Förster resonant energy transfer has no visible effects. Moreover, we show that the charge transfer is assisted by energy migration within the F8BT excited state distribution and that it is dependent on the local micromorphology of the film. Our work improves the current understanding of the polymer:perovskite NC interactions in hybrid films, and it is expected to be relevant for the development of hybrid organic–perovskite optoelectronic devices.

The emission properties of a hybrid polymer:perovskite nanocrystals (NCs) blend film are investigated, evidencing that the main interaction process is not Förster transfer, but instead bidirectional polymer → NC and NC → polymer charge transfer.

Dipole reorientation and local density of optical states influence the emission of light-emitting electrochemical cells

Herein, we analyze the temporal evolution of the electroluminescence of light-emitting electrochemical cells (LECs), a thin-film light-emitting device, in order to maximize the luminous power radiated by these devices. A careful analysis of the spectral and angular distribution of the emission of LECs fabricated under the same experimental conditions allows describing the dynamics of the spatial region from which LECs emit, i.e. the generation zone, as bias is applied. This effect is mediated by dipole reorientation within such an emissive region and its optical environment, since its spatial drift yields a different interplay between the intrinsic emission of the emitters and the local density of optical states of the system. Our results demonstrate that engineering the optical environment in thin-film light-emitting devices is key to maximize their brightness.

Tuning from Quantum Dots to Magic Sized Clusters of CsPbBr3 Using Novel Planar Ligands Based on the Trivalent Nitrate Coordination Complex

We report the first demonstration of using trivalent metal hydrated nitrate coordination complexes (TMHNCCs) as novel passivation ligands to control the synthesis of magic sized clusters (MSCs) and quantum dots (QDs) of CsPbBr₃ perovskite at room temperature. We can easily tune from QDs to MSCs or produce a mixture of the two by changing the amount of TMHNCC ligands used, with more ligands favoring MSCs. The original TMHNCC introduced, aluminum nitrate nonahydrate [ANN, Al(NO₃)₃·9H₂O], led to the production of aluminum dihydroxide nitrate tetrahydrate {ADNT, [Al(OH)₂(NO₃)]·4H₂O}, with the assistance of oleic acid (OA) and oleylamine (OAm). Through several control experiments, we determined that ADNT is the primary ligand for effectively passivating the MSCs and QDs, with OAm being essential for deprotonating ANN and OA for adjusting the pH of the reaction system. We suggest that ADNT is planar on the surface of the MSCs or QDs with its NO₃^- and OH^- groups binding to the Cs⁺ and Pb²⁺ defect sites and Al³⁺ binding to the Br^- defect sites of the MSCs or QDs.

LEDs using halide perovskite nanocrystal emitters

The emerging family of lead-halide perovskite (LHP) nanocrystal emitters has shown impressive achievements in solid-state light-emitting applications. With luminous efficiency comparable to that of organic light-emitting diodes, LHP light-emitting diodes (PeLEDs) have demonstrated a wide colour gamut with high colour purity and a widely tunable range of emissive wavelengths across the whole visible range. Herein, the understanding of LHP nanocrystals in light emission and the resulting PeLEDs are reviewed. Additionally, key features of LHP nanocrystal emitters applied in PeLEDs and guidelines towards realizing high-performance devices are discussed.

Millimeter-Sized Single-Crystal CsPbrB3/CuI Heterojunction for High-Performance Self-Powered Photodetector

Millimeter-sized CsPbBr₃ single crystals were prepared via a facile solvent-evaporation method in ambient environment. The heterojunction between p-type CuI and n-type CsPbBr₃ was formed by a simple immersion process. The as-integrated CsPbBr₃/CuI device exhibits a good rectifying behavior (ratio of 250 at ±2 V). In particular, the photodetector shows excellent self-powered characteristics under 540 nm light illumination, including high photocurrent (near 100 nA); high photosensitivity (on/off ratio of 1.5 × 10³); fast response speed (0.04/2.96 ms); and good wavelength selectivity (565-525 nm), responsivity (1.4 mA W^-1), and detectivity (6.2 × 10¹⁰ Jones). This work provides a simple, low-cost, and effective method for preparing millimeter-level CsPbBr₃ single crystals. The simple device architecture further provides a promising approach for fabricating high-performance self-powered photodetectors.

Room-Temperature Broadband Light Emission from Hybrid Lead Iodide Perovskite-Like Quantum Wells: Terahertz Spectroscopic Investigation of Metastable Defects

The properties of mid-band-gap electronic states are central to the potential application of self-assembled, hybrid organic-inorganic perovskite-like quantum wells in optoelectronic technologies. We investigate broadband light emission from mid-band-gap states in fast-forming hybrid organic lead iodide quantum wells at room temperature. By comparing temperature- and intensity-dependent photoluminescence (PL) spectra emitted from butyl ammonium spaced inorganic layers, we propose that structural defects in a metastable material phase trap excitons and cause broadband light emission spanning wavelengths between 600 and 1000 nm. We use temperature-dependent terahertz time-domain spectroscopy to correlate changes in the subgap PL emission with changes in the chemical bonding of the inorganic octahedral layer. Our results provide new fundamental physical insights into the array of mechanisms capable of inducing broadband light emission from low-dimensional perovskite-like materials central to their application in future optoelectronic technologies and novel spectroscopic tools to characterize these states.

Acid-Amine Equilibria for Formation and Long-Range Self-Organization of Ultrathin CsPbBr3 Perovskite Platelets

Impact of acid-amine equilibrium for triggering the formation of CsPbBr₃ platelets and subsequent long-range self-assembly as a function of acid concentration is reported. The study was performed by treating Cs precursor followed by oleic acid to the ongoing process of L₂PbBr₄ layered perovskites formation at room temperature, and this led to the thinnest possible platelets of CsPbBr₃ with one atomic layer of Cs insertion. These platelets form self-assembly in the micrometer range, and this ordering was tuned as a function of oleic acid concentration and reaction time. With evidence obtained from in situ live monitoring by optical microscopy of these assemblies during the ongoing reaction in solution and analyzing the collected samples ex situ by electron microscopy, it was established that these long-range 1D organizations of platelets took place in solution. Details of the insights of the formation, self-assembly, and impact of different reaction parameters in the formation of these platelets are investigated and reported in this Letter.

Performance analysis of PQDCF-coated silicon image sensor using Monte-Carlo ray-trace simulation

Perovskite quantum dots embedded composite film (PQDCF) exhibits strong photoluminescence emissions and is expected to be excellent down-shifting material for enhancing ultraviolet (UV) response of silicon devices. In this work, light conversion process is analyzed by combining the experiments with Monte-Carlo ray-trace simulation. Results show that external quantum efficiency (EQE) in the UV region was mainly determined by absorption loss and match of peak wavelength. Moreover, resolution was correlated with thickness and reabsorption. This conclusion provides a guideline for designing novel materials with enhanced UV sensitivity and an EQE of 28% is predicted. Our experimental results showed that the use of red emissive PQDCF achieved an EQE of 20%.

Facile Synthesis of Stable and Highly Luminescent Methylammonium Lead Halide Nanocrystals for Efficient Light Emitting Devices

Metal halide perovskites are promising candidates for use in light emitting diodes (LEDs), due to their potential for color tunable and high luminescence efficiency. While recent advances in perovskite-based light emitting diodes have resulted in external quantum efficiencies exceeding 12.4% for the green emitters, and infrared emitters based on 3 D/2D mixed dimensional perovskites have exceeded 20%, the external quantum efficiencies of the red and blue emitters still lag behind. A critical issue to date is creating highly emissive and stable perovskite emitters with the desirable emission band gap to achieve full-color displays and white LEDs. Herein, we report the preparation and characterization of a highly luminescent and stable suspension of cubic-shaped methylammonium lead triiodide (CH₃NH₃PbI₃) perovskite nanocrystals, where we synthesize the nanocrystals via a ligand-assisted reprecipitation technique, using an acetonitrile/methylamine compound solvent system to solvate the ions and toluene as the antisolvent to induce crystallization. Through tuning the ratio of the ligands, the ligand to toluene ratio, and the temperature of the toluene, we obtain a solution of CH₃NH₃PbI₃ nanocrystals with a photoluminescence quantum yield exceeding 93% and tunable emission between 660 and 705 nm. We also achieved red emission at 635 nm by blending the nanocrystals with bromide salt and obtained perovskite-based light emitting diodes with maximum electroluminescent external quantum efficiency of 2.75%.

Highly Efficient and Environmentally Stable Flexible Color Converters Based on Confined CH3NH3PbBr3 Nanocrystals

In this work, we demonstrate a synthetic route to attain methylammonium lead bromide (CH₃NH₃PbBr₃) perovskite nanocrystals (nc-MAPbBr₃, 1.5 nm < size < 3 nm) and provide them with functionality as highly efficient flexible, transparent, environmentally stable, and adaptable color-converting films. We use nanoparticle metal oxide (MOx) thin films as porous scaffolds of controlled nanopores size distribution to synthesize nc-MAPbBr₃ through the infiltration of perovskite liquid precursors. We find that the control over the reaction volume imposed by the nanoporous scaffold gives rise to a strict control of the nanocrystal size, which allows us to observe well-defined quantum confinement effects on the photo-emission, being the luminescence maximum tunable with precision between λ = 530 nm (green) and λ = 490 nm (blue). This hybrid nc-MAPbBr₃/MOx structure presents high mechanical stability and permits subsequent infiltration with an elastomer to achieve a self-standing flexible film, which not only maintains the photo-emission efficiency of the nc-MAPbBr₃ unaltered but also prevents their environmental degradation. Applications as adaptable color-converting layers for light-emitting devices are envisaged and demonstrated.