Materials For Light-emitting Diodes Research Articles

Internal Electric Field Manipulates Exciton-Phonon Couplings in Single Lead Halide Perovskite Nanocrystals.

Lead halide perovskite nanocrystals (NCs) have attracted much attention as materials for light-emitting diodes and quantum light sources. A deep understanding of exciton-phonon couplings is essential for obtaining a narrow emission line, weak phonon-sideband photoluminescence (PL), and a long exciton coherence time, which are especially useful for high-color-purity quantum-light-source applications. Here, we report the PL spectra of single CsPbBr3 NCs at 5.5 K as a function of the applied electric field. The exciton peak energy shows an asymmetric parabolic shift for positive and negative biases, implying the presence of a spontaneously generated internal electric field in the NCs when no field is applied. Both the internal electric field and exciton-phonon couplings become larger in smaller NCs, and they have a positive correlation with each other. Our findings show that the exciton-phonon couplings can be manipulated with an electric field, which dominates the PL properties of perovskite NCs.

Disorder–Order transition and Metal-to-Metal charge transfer induced rare Orangish-Red emission in Bi3+-Activated double perovskite phosphors

Revealing and regulating the photoluminescence behaviors of Bi3+-activated phosphors play a crucial role in the exploration of high-quality photoluminescent materials for phosphor-converted white light-emitting diodes (pc-WLEDs). However, the existing development strategies of Bi3+-doped red phosphors are still scarce. Herein, a series of excellent NaLaScNbO6:Bi3+, Li+ orangish-red phosphors were synthesized via a high-temperature solid-state reaction. Under 370 nm NUV excitation, the optimal sample emits an orangish-red light with a peak wavelength of 625 nm, full width at half maximum of 123 nm. The A-site disorder–order transition induced by Bi3+ doping in NaLaScNbO6 double perovskite was first confirmed through Rietveld refinements and high-resolution transmission electron microscopy. The co-doped Li+ as an alkali flux material can effectively promote the layer ordering of the A-site and considerably elevate the inner quantum efficiency from 38.97 to 76.10 %. This remarkable orangish-red luminescence can be attributed to the metal-to-metal charge transfer (between Bi3+ and Nb5+) in conjunction with structural disorder–order transition. The luminous efficiency of the fabricated pc-WLED is 7.63 lm/W. The fabricated pc-WLED shows a high color rendering index (Ra = 92, R9 = 92) that can used in warm white pc-LED. The obtained results provide a fresh perspective and valuable insights into the design of Bi3+-doped red phosphors, establishing a correlation between disorder–order transition and luminescence phenomena.

(Invited) Fundamental Photophysics of Lead Halide Perovskites

Halide perovskites have been receiving significant attention as a new class of semiconductor optoelectronic materials for solar cells, displays, light-emitting diodes, and quantum light sources [1,2]. Their high-quality bulk crystal and nanocrystal samples can be fabricated by simple low-temperature solution processes, and they exhibit extremely high photoluminescence (PL) quantum yields even at room temperature. Optical spectroscopy is one of the most versatile techniques for characterizing new semiconductor materials. In this work, we discuss optical properties of ABX3 lead halide perovskites as new solar cell and light-source materials.(1) Band-edge electronic structures: ABX3-type halide perovskites are direct-gap semiconductors with unique band structures because of strong spin-orbit couplings [3]. The electronic structures of lead halide perovskites are dominantly determined by the lead-halide octahedra. Nonlinear optical spectroscopy [4-6] and magneto-optical spectroscopy [7] revealed the Kane energy, spin-orbit splitting energy, exciton binding energy, and reduced exciton mass of lead halide perovskites.(2) Free carrier luminescence in bulk single crystals: Strong PL with no Stokes shift is caused by the band-to-band free carrier recombination in low-bandgap iodide perovskites and the exciton recombination in wide-bandgap chloride perovskites [4,8,9]. No impurity and defect luminescence appear at room temperature. Intrinsic up-conversion PL (anti-Stokes PL) is clearly observed in perovskites, because of strong electron-phonon interactions [10,11]. In thick samples, photon recycling (photon emission and reabsorption) and carrier diffusion processes determine the PL spectra and dynamics [12,13].(3) Exciton luminescence in nanocrystal quantum dots: Single dot PL spectroscopy revealed that the recombination dynamics of excitons, trions, and biexcitons cause unique optical responses of nanocrystal quantum dots (for example, PL blinking and spectral diffusion) [14,15]. Nonradiative Auger recombination of trions and biexcitons dominates the PL dynamics at room temperature [16,17]. At low temperatures, multipeak structures appear in the PL spectra and they originate from the exciton, trion, biexciton, and their LO-phonon assisted PL [19,20]. We determined the nanocrystal size dependence of the trion and biexciton binding energies [19,21].Part of this work was supported by JST-CREST (Grant No. JPMJCR21B4), NEDO-GI (Grant No. JPNP21016), and JSPS KAKENHI (Grant No. JP19H05465). Y. Kanemitsu and Handa, Jpn. J. Appl. Phys. 57, 090101 (2018).T. Handa et al., Phys. Chem. Chem. Phys. 22, 26069 (2020).Y. Yamada et al., Appl. Phys. Express 7, 032302 (2014).T. Yamada et al., Phys. Rev. Lett. 120, 057404 (2018).K. Ohara et al., Phys. Rev. Mater. 3, 111601(R) (2019).K. Ohara et al., Phys. Rev. B 103, L041201 (2021).Y. Yamada et al., Phys. Rev. Lett. 126, 237401 (2021).T. Yamada et al., J. Phys. D: Appl. Phys. 54, 383001 (2021).Y. Yamada et al., J. Am. Chem. Soc. 136, 11610 (2014).M. Nagai, et al., Phys. Rev. Lett. 121, 145506 (2018).T. Yamada et al, Phys. Rev. Materials 3, 024601 (2019).Y. Yamada et al., J. Am. Chem. Soc. 137, 10456 (2015).T. Yamada et al., Phys. Rev. Applied. 7, 014001 (2017).Y. Kanemitsu, J. Chem. Phys. 151, 170902 (2019).G. Yumoto and Y. Kanemitsu, Phys. Chem. Chem. Phys. 24, 22405 (2022).N. Yarita et al., J. Phys. Chem. Lett. 8, 1413 (2017).N. Yarita et al., Phys. Rev. Mater. 2, 116003 (2018).S. Masada et al., Nano Lett. 20, 4022 (2020).K. Cho et al., Nano Lett. 21, 7206 (2021).K. Cho et al., Nano Lett. 22, 7674 (2022).K. Cho et al., ACS Nano 18, 5723 (2024).

Benchmark computations of nearly degenerate singlet and triplet states of N-heterocyclic chromophores. I. Wavefunction-based methods.

In this paper, we investigate the role of electron correlation in predicting the S1-S0 and T1-S0 excitation energies and, hence, the singlet-triplet gap (ΔEST) in a set of cyclazines, which act as templates for potential candidates for fifth generation organic light emitting diode materials. This issue has recently garnered much interest with the focus being on the inversion of the ΔEST, although experiments have indicated near degenerate levels with both positive and negative being within the experimental error bar [J. Am. Chem. Soc. 102, 6068 (1980), J. Am. Chem. Soc. 108, 17(1986)]. We have carried out a systematic and exhaustive study of various excited state electronic structure methodologies and identified the strengths and shortcomings of the various approaches and approximations in view of this challenging case. We have found that near degeneracy can be achieved either with a proper balance of static and dynamic correlation in multireference theories or with state-specific orbital corrections, including its coupling with correlation. The role of spin contamination is also discussed. Eventually, this paper seeks to produce benchmark numbers for establishing cost-effective theories, which can then be used for screening derivatives of these templates with desirable optical and structural properties. Additionally, we would like to point out that the use of domain-based local pair natural orbital-similarity transformed EOM-coupled cluster singles and doubles as the benchmark for ΔEST [as used in J. Phys. Chem. A 126(8), 1378 (2022), Chem. Phys. Lett. 779, 138827 (2021)] is not a suitable benchmark for these classes of molecules.

Influence of carbon dots as modifier and SiO2 shell coating as a protecting layer in YAlO3:Cr3+ phosphors for multimodal applications

This study focuses on the synthesis of SiO2-coated carbon dots (CDs) grafted onto YAlO3:Cr3+ (YAP:Cr3+) nanophosphors (NPs) through a combustion method. The CDs enhance the absorption cross-section of Cr3+ ions, significantly boosting the luminescence of YAP:Cr3+ by 19.29-fold. Further improvement is achieved with a SiO2 coating, leading to a 48.73-fold increase in photoluminescence intensity. The NCs are colour tunable, with emissions ranging from pinkish-red to blue, depending on the concentration of CDs and the excitation wavelength. These properties make them suitable for diverse applications, such as ratio metric fluorescence sensors for detecting Fe3+ ions within the 0–350 µM range, with high sensitivity (0.2 µM) and a low detection limit (4.93 μM). Additionally, they serve as material for white light-emitting diodes (W-LEDs), achieving CIE coordinates of (0.31, 0.30) and a rendering index of 94. The NCs also function as an optical thermometer with a sensitivity of 0.31 % K−1 at 320 K, making them ideal for temperature sensing applications. Moreover, their stability and dual-emissive nature make them highly effective in latent fingerprints (LFPs) detection, enabling high-resolution, level III fingerprint analysis. The dual emission properties of CDs and Cr3+ ions position these NCs as multifunctional materials, suitable for optical sensing, lighting, and security applications.

Enhancing the emissive film quality: A new role of TADF materials for high-performance blue perovskite light-emitting diodes

Thermally activated delayed fluorescence (TADF) materials are widely used in the field of organic light-emitting diodes (OLEDs) because they can capture both singlet and triplet excitons for light emission. However, only scare attention has been paid to the application of TADF materials in perovskite LEDs (PeLEDs) and the understanding of effects of TADF materials in PeLEDs is limited. In this study, a new role of TADF materials for achieving high-quality perovskite films to enhance the performance of PeLEDs is emphasized. TADF materials are introduced into quasi-2D blue PeLEDs to assist in the crystallization of perovskites during film annealing and ensure the formation of high-quality films with reduced defects, enhancing device performance. Additionally, a step-like hole transport layer has been constructed to reduce the hole transport barrier, which can further enhance the performance of PeLEDs. The resultant blue PeLEDs exhibits an external quantum efficiency of 5.44 %, which is 12.7-fold higher than that of the control device. Furthermore, a turn-on voltage of 2.6 V is achieved, which is the lowest for TADF-based blue PeLEDs. The findings may not only unlock a new role of TADF materials in blue PeLEDs, but also provide an alternative pathway to achieve high-performance PeLEDs.

Progress, application and prospect of rare earth-based perovskite light-emitting diodes

Perovskites recently become star materials in light-emitting diodes (LEDs) field due to their high color purity, tunable emission spectra, and cost-effectiveness. However, the commercial applications of perovskite LEDs are hampered by inferior lattice stability of perovskite materials. Successful modification of functional materials is a promising strategy towards efficient and stable perovskite LEDs. Rare earth (RE) metals are incorporated into the perovskite lattice, including double perovskites, by occupying the B-site or A-site in perovskite such as ABX3 or A2BB'X6, forming the RE-based perovskite. Doping with RE ions enables precise control emission color of materials across a broad spectrum ranging from ultraviolet to near infrared. Moreover, this strategy reduces the energy loss in electron relaxation process and enhances electroluminescence intensity of LED device, thereby improving the potential of commercial applications of perovskite LEDs. This review provides a comprehensive and systematic summarization of recent progress and challenges in RE-based perovskite materials (structure types, luminescence mechanism and synthesis methods) and LEDs (device structures and main applications) to provide some enlightening insights for realization of efficient and stable RE-based perovskite LEDs.

Enhanced luminescence of CaO:Eu2+ red phosphor in glass for high-power warm LED

Highly emissive and stable red phosphors are vital for the warm Light Emitting Diode (LED). Herein, blue-light-excited CaO:Eu2+ red phosphors were prepared using the carbonation method, coupled with the double crucible carbon reduction technology. The addition of GeO2 and SnO2 significantly enhanced the photoluminescence (PL) intensity and quantum efficiency. Furthermore, a phosphor-in-glass (PiG) made from an improved luminescent CaO:Eu2+ was developed and utilized for LED applications. Such PiG samples considerably improved the stability of CaO:Eu2+ phosphors. The excellent stability, high color rendering index (Ra) value of 87.7 and low correlated color temperature (CCT) of 4469 K confirmed the resulting CaO:Eu2+-based PiG as a promising material for white light-emitting diodes (WLEDs).

Defect passivation with spectral shift for improved efficiency and stability of quasi-2D blue perovskite light emitting diodes

Metal halide perovskites are emerging as promising materials for next-generation light-emitting diodes (LEDs), owing to their cost-effectiveness, facile manufacturing, and excellent optoelectronic properties including a narrow emission-line full width at half maximum, high photoluminescence quantum yield, and spectral stability. However, blue-emission perovskite LEDs (PeLEDs) exhibit perovskite phase segregation and halogen ion migration during operation, attributed to crystal defects, halogen vacancies, and phase instability of mixed-halide perovskites. These defects compromise the spectral stability of blue-emitting PeLEDs, resulting in an undesirable color shift toward longer wavelengths. In this study, we introduce a dynamic treatment with phenylphosphonic dichloride (PPOCl2) to address these challenges and achieve blue-emitting PeLEDs. The chloride in PPOCl2 penetrates the quasi-2D sky-blue perovskite, reducing halide defects. Meanwhile, the phosphonic group forms covalent bonds with undercoordinated Pb on the perovskites, effectively passivating defects. PPOCl2-treated perovskite exhibits a spectral blue shift toward a deep-blue wavelength (≤467 nm), enhancing electroluminescence performance. The quasi-2D PPOCl2-treated PeLEDs achieve a maximum external quantum efficiency of 2.31 % with an emission peak at 488 nm. Dynamic treatment with PPOCl2 shows the potential to improve the performance and stability of blue emission perovskite-based LEDs, providing a spectral shift mechanism to achieve deep-blue emission in PeLEDs.

Machine Learning-Driven Precise Design of Stable OLED Materials: Predicting and Enhancing Multi-State C-N Bond Dissociation Energies

The intrinsic stability of organic light-emitting diode (OLED) materials critically hinges on the bond dissociation energies (BDEs) of fragile bonds, particularly C-N bonds. Despite the necessity of considering BDEs in multiple electronic states due to the complex working conditions of organic materials in OLED devices, comprehensive exploration remains challenging. Herein, we constructed a high-quality dataset, CNBDE-24, comprising nearly 1500 data points for BDEs across multiple electronic states, obtained through an active learning-guided density functional theory (DFT) calculation strategy. Machine learning models trained on the CNBDE-24 dataset exhibit excellent accuracy in predicting BDEs for OLED materials in neutral, triplet excited (T1), and anionic states, achieving an adjusted coefficient of determination exceeding 0.90 on the test set and bypassing the need for high-cost calculation. Moreover, utilizing neutral state BDEs as pre-training data significantly reduces model error and provides deeper insights into the relationships between different BDEs. We find that BDEs in neutral are influenced by the electronic properties of the nitrogen atom, as indicated by descriptors such as Gasteiger charges. Incorporating C-N bonds into aromatic systems and slightly dispersing N atom charges can inherently increase multi-state BDEs without altering luminescent properties. Additionally, anionic BDEs are determined by the extent of charge transfer during bond cleavage and can be regulated by modifying the C-side fragment. High-throughput virtual screening reveals a new stable purple emitter with a dominant 0–0 transition at 360 nm, which was validated through DFT and excited-state property evaluations. Strategies for enhancing BDEs in multiple resonance thermally activated delayed fluorescence materials without altering excited-state properties are also demonstrated.

Recent progress in circularly polarized multi-resonance thermally activated delayed fluorescence materials for organic light-emitting diodes

Recent progress in circularly polarized multi-resonance thermally activated delayed fluorescence materials for organic light-emitting diodes

Solvent mediated synthesis of multicolor narrow bandwidth emissive carbon quantum dots and their potential in white light emitting diodes

The development of efficient and environmentally sustainable materials for white light-emitting diodes (WLEDs) is of paramount importance in the field of lighting technology. In this study, we present a solvent-modulated synthesis approach for the fabrication of multicolor narrow-bandwidth emissive carbon quantum dots (CQDs) as a promising solution for constructing WLEDs. The synthesis method involves the controlled reaction of organic precursors in different solvent environments, leading to the formation of CQDs with distinct emission wavelengths with a relatively small full width at half maximum, ranging from 28 to 42 nm. Moreover, these synthesized multicolor CQDs demonstrate a remarkably high fluorescence quantum yield of up to 65%, indicating their potential for constructing efficient WLED when incorporated in polymer matrix and coated on the surface of blue light-emitting diode (LED).

Dimesitylborane as Electron Accepting Unit in High Performance Yellow Single-Layer Phosphorescent Organic Light Emitting Diode.

A new host material for Single-Layer Phosphorescent Organic Light-Emitting Diodes (SL-PhOLED) is reported, namely SPA-2-FDMB, using the dimesitylborane (DMB) fragment as an acceptor unit. The molecular design is constructed on the general donor-spiro-acceptor architecture, which consists of connecting, via a spiro bridge, a donor and an acceptor units in order to avoid strong interaction between them. The DMB fragment is known for many electronic applications (notably Aggregation-Induced Emission) but has not been used yet for SL-PhOLED applications. This appears particularly interesting, as the development of this simplified technology has shown that only a few electron-accepting fragments such as diphenylphosphine oxide can provide high-performance devices. Herein, the yellow-emitting SL-PhOLED using SPA-2-FDMB as host presents an External Quantum Efficiency of 8.1% (Current Efficiency of 24.9cd.A-1) with a low threshold voltage of 2.6V. As SPA-2-FDMB presents a sharp HOMO/LUMO difference, the good matching of HOMO and LUMO energy levels with the Fermi level of the electrodes is responsible for these performances. The low LUMO level of -2.61eV also appears particularly important. These performances are, to date, the highest reported for a yellow/orange-emitting SL-PhOLED and show the potential of DMB unit in the single-layer technology.

Suppression of Initial Degradation via an Interfacial Charge-Induced Overshooting Effect in Solution-Processed Organic Light-Emitting Diodes.

As the chemical stability of organic materials in organic light-emitting diodes (OLEDs) greatly impacts devices' lifetime, a thoughtful and advanced design of materials and device structures is necessary. In our work, we have achieved lifetime enhancement at its initial stage for solution-processed OLEDs. This improvement was realized through the implementation of a double electron transporting layer (dETL) composed of 2-[4-(9,10-dinaphthalen-2-yl-anthracen-2-yl)-phenyl]-1-phenyl-1H-benzoimidazole (ET) and hydroxyquinolinolato-lithium (Liq). A giant surface potential was generated at the surface of a constituent electron transport layer (ETL) that contained a higher concentration of Liq with high polarity. This giant surface potential simultaneously promoted the injection of trapped/accumulated electrons through the interface within dETL and the injection of holes from the anode, generating more exciton recombination events and ultimately enhancing efficiency by 133.0% and lifetime LT95 (luminance dropped by 5%) by 300% with an overshooting effect. Additionally, the degradation at the emitting layer was mitigated by shifting the degradation zone to the dETL, which was evidenced by laser desorption/ionization-time-of-flight (LDI-TOF) mass spectroscopy.

The first principle calculations of band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites

This study investigates the band offsets among Cs2(Ti, Zr, Hf)X6 double halide perovskites. Valence band offsets (VBO) and conduction band offsets (CBO) were calculated using density functional theory (DFT) with the Perdew–Burke-Ernzerhof (PBE) functional and the hybrid Heyd–Scuseria–Ernzerhof (HSE) functional, employing the supercell technique. This technique offers greater accuracy and reliability by explicitly calculating the potential differences at the interface. A critical factor influencing the results is the contribution of the dipole potential (VD), which induces shifts in the VBO and CBO by approximately 0.2 to 0.6 eV relative to values predicted by the electron affinity rule. This discrepancy arises from the inclusion of interface-specific effects, such as charge redistribution and polarization. Additionally, the findings indicate that the energy band alignments among these compounds are type-I within the same group of halides, with nearly identical lattice constants for Zr- and Hf-based compounds due to their similar ionic radii. These results provide valuable insights for the design of heterostructures in electronic applications and highlight the potential of Cs2(Ti, Zr, Hf)X6 compounds as efficient materials for solar cells, light-emitting diodes, and photodetectors.

Interfacial Dipole Engineering for Energy Level Alignment in NiOx-Based Quantum Dot Light-Emitting Diodes.

The solution-derived non-stoichiometric nickel oxide (NiOx) is a promising hole-injecting material for stable quantum dot light-emitting diodes (QLEDs). However, the carrier imbalance due to the misalignment of energy levels between the NiOx and polymeric hole-transporting layers (HTLs) curtails the device efficiency. In this study, the modification of the NiOx surface is investigated using either 3-cyanobenzoic acid (3-CN-BA) or 4-cyanobenzoic acid (4-CN-BA) in the QLED fabrication. Morphological and electrical analyses revealed that both 4-CN-BA and 3-CN-BA can enhance the work function of NiOx, reduce the oxygen vacancies on the NiOx surface, and facilitate a uniform morphology for subsequent HTL layers. Moreover, it is found that the binding configurations of dipole molecules as a function of the substitution position of the tail group significantly impact the work function of underlying layers. When integrated in QLEDs, the modification layers resulted in a significant improvement in the electroluminescent efficiency due to the enhancement of energy level alignment and charge balance within the devices. Specifically, QLEDs incorporating 4-CN-BA achieved a champion external quantum efficiency (EQE) of 20.34%, which is a 1.8X improvement in comparison with that of the devices utilizing unmodified NiOx (7.28%). Moreover, QLEDs with 4-CN-BA and 3-CN-BA modifications exhibited prolonged operational lifetimes, indicating potential for practical applications.

High-efficiency RbASiF6:Mn4+ (A = K, Cs) phosphors obtained by one-step green synthesis method

Red-emitting Mn4+-doped fluoride phosphors are recognized as promising materials for high-performance warm white light-emitting diodes (WLEDs). However, the extensive use of toxic hydrofluoric acid in traditional synthesis methods hinders their development and commercialization. Furthermore, the traditional solid-phase method often has cumbersome sintering steps, high temperature, long holding time, and certain safety hazards, so it is very necessary to develop a green synthesis method with simple steps and low energy consumption. In this study, a low-temperature solid-state method is proposed to synthesize RbASiF6:Mn4+ (A = K, Cs) phosphors by one step. Optimal emission intensities were observed at Mn4+ concentrations of 1.2 % in RbKSiF6 and 2.1 % in RbCsSiF6. These phosphors demonstrated high thermal stability. At 423 K, the photoluminescence intensities of RbKSiF6:1.2 %Mn4+ and RbCsSiF6:2.1 %Mn4+ reached 114 % and 87 % of their respective values at room temperature. Meanwhile, the chromaticity shifts were almost negligible, and high color purity was achieved for both phosphors. The electro-optical performance of WLED devices utilizing these phosphors, in combination with YAG:Ce3+ and GaN chips, showed high color rendering indices (CRI) and low correlated color temperatures (CCT) across varying currents. Specifically, under a driving current of 20 mA, the device incorporating RbKSiF6:1.2 %Mn4+ exhibited a CRI of 94 and a CCT of 3732 K, with a luminous efficacy of 61 lm/W. These findings highlight the potential of green-synthesized RASFM phosphors in advancing the application of warm WLEDs.

Efficient thermally activated delayed fluorescence materials from symmetric anthraquinone derivatives for high-performance red OLEDs

Constructing efficient red thermally activated delayed-fluorescence (TADF) materials for high-performance organic light-emitting diodes (OLEDs) remains challenging due to the formidable barrier of energy gap law. In this work, a design strategy of connecting two donor units to the adjacent positions of electron acceptor is proposed for creating red luminescent materials, and four Y-shaped TADF molecules consisting of strong electron-withdrawing anthraquinone (AQ) acceptor and triphenylamine or acridine-based donors are designed and synthesized. They exhibit strong red emissions (604−618 nm) in toluene solutions and orange/red emissions (566−608 nm) with good photoluminescence quantum yields (43−68%) in doped films, and enjoy small singlet-triplet energy gaps (0.02−0.10 eV) and fast reverse intersystem crossing processes (1.5–7.3 × 105 s−1), which are attributed to the unique Y-shape structure. A maximum external quantum efficiency of 19.5% with an electroluminescence peak at 616 nm is achieved for AQ-PTPA-based red doped device, representing the highest level for red TADF-OLEDs based on AQ acceptor in the literature. This work can provide guidance for the design of efficient red delayed-fluorescence molecules for the application in OLEDs.

Near Room Temperature Solvothermal Growth of Ferroelectric CsPbBr3 Nanoplatelets with Ultralow Dark Current.

CsPbBr3 exhibits outstanding optoelectronic properties and thermal stability, making it a coveted material for detectors, light-emitting diodes, and solar cells. Despite observations of ferroelectricity in CsPbBr3 quantum dots, synthesizing bulk ferroelectric CsPbBr3 crystals has remained elusive, hindering its potential in next-generation optoelectronic devices like optical switches and ferroelectric photovoltaics. Here, a breakthrough is reported: a novel solvothermal technique enabling the growth of ferroelectric CsPbBr3 nanoplatelets with lateral dimensions in the tens of micrometers. This represents a significant step toward achieving large-area ferroelectric CsPbBr3 crystals. Unlike traditional methods, this approach allows for growth and crystallization of CsPbBr3 in alcohol solutions by enhancing precursor solubility. This study confirms the ferroelectric nature of these nanoplatelets using second harmonic generation, electrical characterizations, and piezoresponse force microscopy. This work paves the way for utilizing ferroelectric CsPbBr3 in novel optoelectronic devices, significantly expanding the potential of this material and opening doors for further exploration in this exciting field.

Suppressing Formation of Buried Defects during Annealing Enables Bright Perovskite Light-Emitting Diodes.

Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is a promising hole-transporting material for perovskite light-emitting diodes (PeLEDs). However, intrinsic luminance quenching at the PEDOT:PSS/perovskite interface causes deterioration of performance. Here, we develop a facile and effective strategy to passivate the interface defects via the modification of PEDOT:PSS by l-norvaline. As a pre-buried additive, l-norvaline not only reacts with PEDOT:PSS, but also forms the coordination and hydrogen bond with perovskite. We demonstrated that the generation of buried defects at the PEDOT:PSS/perovskite interface originates from the crystallization process of the perovskite film during annealing by in-situ photoluminescence measurements. The surface of l-norvaline-modified PEDOT:PSS can passivate the interfacial defects and inhibit exciton quenching. As a result, the PeLED shows a good device performance with a luminance of 80089 cd m-2 at 509 nm and an external quantum efficiency of 13.04%.