Nearly 100% Efficiency Enhancement of CH3NH3PbBr3 Perovskite Light-Emitting Diodes by Utilizing Plasmonic Au Nanoparticles

Light management for perovskite light-emitting diodes

Perovskite light-emitting diodes (LEDs) have reached external quantum efficiencies of over 20% for various colours, showing great potential for display and lighting applications. Despite the internal quantum efficiencies of the best-performing devices already approaching unity, around 80% of the internally generated photons are trapped in the devices and lose energy through a variety of lossy channels. Significant opportunities for improving efficiency and maximizing photon extraction lie in the effective management of light. In this Review we analyse light management strategies based on the intrinsic optical properties of the perovskite materials and the extrinsic properties related to device structures. These approaches should allow the external quantum efficiencies of perovskite LEDs to substantially exceed the conventional limits of planar organic LED devices. By revisiting lessons learned from organic LEDs and perovskite solar cells, we highlight possible directions of future research towards perovskite LEDs with ultrahigh efficiencies.

Effective Blue Light-Absorbing AuAg Nanoparticles in InP Quantum Dots-Based Color Conversion

In typical color-by-blue mode-based quantum dot (QD) display devices, only part of the blue excitation light is absorbed by QD emitters, thus it is accompanied by the leakage of blue light through the devices. To address this issue, we offer, for the first time, the applicability of AuAg alloy nanoparticles (NPs) as effective blue light absorbers in InP QD-based color-by-blue platforms. For this, high-quality fluorescent green and red InP QDs with a double shell scheme of ZnSe/ZnS were synthesized and embedded in a transparent polymer film. Separately, a series of Au/Ag ratio-varied AuAg NPs with tunable plasmonic absorption peaks were synthesized. Among them, AuAg NPs possessing the most appropriate absorption peak with respect to spectral overlap with blue emission are chosen for the subsequent preparation of AuAg NP polymeric films with varied NP concentrations. A stack of AuAg NP polymeric film on top of InP QD film is then placed remotely on a blue light-emitting diode, successfully resulting in systematically progressive suppression of blue light leakage with increasing AuAg NP concentration. Furthermore, the beneficial function of the AuAg NP polymeric overlayer in mitigating undesirable QD excitation upon exposure to ambient lights was further examined.

Enhanced lasing properties of BUBD-1 film with multifunctional buffer layers doped with silver nanoparticles

The organic semiconductor lasers (OSLs) have been seen as a promising light source for future applications. Achieving organic semiconductors with low amplified spontaneous emission (ASE) threshold is a key progress toward the electrically pumped OSLs. In this paper, the ASE properties of CBP: 2wt% BUBD-1 blend films were optimized using buffer layers containing silver nanoparticles (Ag NPs) with different ratios. Both photoluminescence intensity and ASE properties of blend films were optimized when the buffer layer with 25 vol% Ag NPs was introduced. The lowest ASE threshold is 0.47 µJ/Pulse (6.71 µJ/cm²), which reduces 67.6%, and the highest gain factor is 20.14 cm^-1, which enhances 47.8% compared with that without buffer layers. The enhancement of ASE properties of blend films was ascribed to the four functions of the Ag NPs doped buffer layers, including the low refractive index of PMMA and the triple localized surface plasmon resonance (LSPR) effects of Ag NPs in buffer layers. The results show that the buffer layer modified by metal nanoparticles has great application potential in improving the lasing performance of organic small molecules.

Polarity and Ferromagnetism in Two-Dimensional Hybrid Copper Perovskites with Chlorinated Aromatic Spacers

Two-dimensional (2D) organic-inorganic hybrid copper halide perovskites have drawn tremendous attention as promising multifunctional materials. Herein, by incorporating ortho-, meta-, and para-chlorine substitutions in the benzylamine structure, we first report the influence of positional isomerism on the crystal structures of chlorobenzylammonium copper(II) chloride perovskites A₂CuCl₄. 2D polar ferromagnets (3-ClbaH)₂CuCl₄ and (4-ClbaH)₂CuCl₄ (ClbaH⁺ = chlorobenzylammonium) are successfully obtained. They both adopt a polar monoclinic space group Cc at room temperature, displaying significant differences in crystal structures. In contrast, (2-ClbaH)₂CuCl₄ adopts a centrosymmetric space group P 2₁/ c at room temperature. This associated structural evolution successfully enhances the physical properties of the two polar compounds with high thermal stability, discernible second harmonic generation (SHG) signals, ferromagnetism, and narrow optical band gaps. These findings demonstrate that the introduction of chlorine atoms into the interlayer organic species is a powerful tool to tune crystal symmetries and physical properties, and this inspires further exploration of designing high-performance multifunctional copper-based materials.

Bright CdSe/CdS Quantum Dot Light-Emitting Diodes with Modulated Carrier Dynamics via the Local Kirchhoff Law

Addressing the interactions between optical antennas and ensembles of emitters is particularly challenging. Charge transfer and Coulomb interactions complicate the understanding of the carrier dynamics coupled by antennas. Here, we show how Au antennas enhance the luminescence of CdSe/CdS quantum dot assemblies through carrier dynamics control within the framework of the local Kirchhoff law. The Au antennas inject hot electrons into quantum dot assemblies via plasmon-induced hot electron transfer that increases the carrier concentration. Also, the localized surface plasmon resonances of Au antennas favorably tilt the balance between nonradiative Auger processes and radiative recombination in the CdSe core. Eventually, a high bright (125,091.6 cd/m²) deep-red quantum dot light-emitting diode is obtained by combining with Au antennas. Our findings suggest a new understanding of light emission of assembled emitters coupled by antennas, which is of essential interest for the description of light-matter interaction in advanced optoelectronics.

Luminescence enhancement of lead halide perovskite light-emitting diodes with plasmonic metal nanostructures

Metal halide perovskites, as newly emerging light emitters, have been attracting considerable attention on luminescent materials and devices, due to their superior optoelectronic properties and potential practical applications. Recently, perovskite light-emitting diodes (PeLEDs) based on lead halide perovskites (LHPs) have been largely designed and intensively studied in laboratory platforms. However, to satisfy demand and promote their commercialization, it is crucial to improve the efficiency and stability of PeLEDs. Accordingly, the surface-plasmon (SP) effect provides a promising approach to enhance their luminescence, which is realized by incorporating plasmonic metal nanostructures (NSs) into PeLEDs. This review presents a comprehensive overview of the research status and prospect on LHP-based plasmonic PeLEDs together with the corresponding perovskite light-emission films (PeLEFs). Firstly, the recent development of the PeLEDs is briefly introduced. Secondly, the mechanisms and photophysics of the PeLEDs by SP manipulation are simply illustrated and analyzed. Then, the recent progress and achievements on the theoretical and experimental results of SP effect applications in the PeLEDs together with PeLEFs are presented in detail and systematically reviewed. Next, the current challenges and future directions of the PeLEDs are shown and discussed. Finally, a critical summary and outlook of the PeLEDs are summarized and proposed. Our results indicate that this new class of LHP-based plasmonic PeLEDs presents future research fields and demonstrates promising applications in lighting and displays, and further luminescence enhancement in exciton radiation processes and light extraction techniques are a hopeful route to obtain high-performance PeLEDs.

Non-toxic near-infrared light-emitting diodes

Harnessing cost-efficient printable semiconductor materials as near-infrared (NIR) emitters in light-emitting diodes (LEDs) is extremely attractive for sensing and diagnostics, telecommunications, and biomedical sciences. However, the most efficient NIR LEDs suitable for printable electronics rely on emissive materials containing precious transition metal ions (such as platinum), which have triggered concerns about their poor biocompatibility and sustainability. Here, we review and highlight the latest progress in NIR LEDs based on non-toxic and low-cost functional materials suitable for solution-processing deposition. Different approaches to achieve NIR emission from organic and hybrid materials are discussed, with particular focus on fluorescent and exciplex-forming host-guest systems, thermally activated delayed fluorescent molecules, aggregation-induced emission fluorophores, as well as lead-free perovskites. Alternative strategies leveraging photonic microcavity effects and surface plasmon resonances to enhance the emission of such materials in the NIR are also presented. Finally, an outlook for critical challenges and opportunities of non-toxic NIR LEDs is provided.

Materials, photophysics and device engineering of perovskite light-emitting diodes

Here we provide a comprehensive review of a newly developed lighting technology based on metal halide perovskites (i.e. perovskite light-emitting diodes) encompassing the research endeavours into materials, photophysics and device engineering. At the outset we survey the basic perovskite structures and their various dimensions (namely three-, two- and zero-dimensional perovskites), and demonstrate how the compositional engineering of these structures affects the perovskite light-emitting properties. Next, we turn to the physics underpinning photo- and electroluminescence in these materials through their connection to the fundamental excited states, energy/charge transport processes and radiative and non-radiative decay mechanisms. In the remainder of the review, we focus on the engineering of perovskite light-emitting diodes, including the history of their development as well as an extensive analysis of contemporary strategies for boosting device performance. Key concepts include balancing the electron/hole injection, suppression of parasitic carrier losses, improvement of the photoluminescence quantum yield and enhancement of the light extraction. Overall, this review reflects the current paradigm for perovskite lighting, and is intended to serve as a foundation to materials and device scientists newly working in this field.

Supramolecular [Na(15-crown-5)]+ cations anchored to face-sharing octahedral lead bromide chains featuring a rotor-like one-dimensional perovskite with a reversible isostructural phase transition near room temperature

A 1D rotor-like organic perovskite, {[Na(15-crown-5)]PbBr3}n, features a high-κ nature and experiences a reversible isostructural phase transition near room temperature.

Giant Enhancement of Radiative Recombination in Perovskite Light-Emitting Diodes with Plasmonic Core-Shell Nanoparticles

The integration of nanoparticles (NPs) into functional materials is a powerful tool for the smart engineering of their physical properties. If properly designed and optimized, NPs possess unique optical, electrical, quantum, and other effects that will improve the efficiency of optoelectronic devices. Here, we propose a novel approach for the enhancement of perovskite light-emitting diodes (PeLEDs) based on electronic band structure deformation by core-shell NPs forming a metal-oxide-semiconductor (MOS) structure with an Au core and SiO2 shell located in the perovskite layer. The presence of the MOS interface enables favorable charge distribution in the active layer through the formation of hole transporting channels. For the PeLED design, we consider integration of the core-shell NPs in the realistic numerical model. Using our verified model, we show that, compared with the bare structure, the incorporation of NPs increases the radiative recombination rate of PeLED by several orders of magnitude. It is intended that this study will open new perspectives for further efficiency enhancement of perovskite-based optoelectronic devices with NPs.

Plasmonic random laser from dye-doped cholesteric liquid crystals incorporating silver nanoprisms

Plasmonic random lasers have been demonstrated in combining dye-doped cholesteric liquid crystals (DD-CLCs) and silver nanoparticles (AgNPs). The DD-CLC laser reveals the lowest threshold and highest slope efficiency through the localized surface plasmon resonance of AgNPs with the best coupling of the emission spectrum of lasing dye and resonance of electron oscillation on the metal surface. Thermal control of the DD-CLC lasers has been achieved to simultaneously shift the long- and short-edge lasing peaks. By the α-stable analysis, the DD-CLC random laser (RL) reveals heavy tail distribution with relatively low α∼1.06 to show the Lévy behavior. Owing to its low spatial coherence, the DD-CLC RL has been demonstrated to produce a speckle-reduced image with a lower contrast of about 0.04.

Bifacial passivation towards efficient FAPbBr3-based inverted perovskite light-emitting diodes

A unique technique to passivate both bottom and top sides of perovskite has been successfully developed to achieve highly efficient inverted perovskite light-emitting diodes (PeLEDs). For the bottom passivation, an organic/inorganic hybrid electron transporting layer (ETL) replaces the widely adopted inorganic ETL to overcome the disadvantages of the pure inorganic ETL. The ZPM (ZnO-in-polymer matrix) ETL, which consists of ZnO nanoparticles blended into polyvinylpyrrolidone, not only passivates the surface defects of ZnO nanoparticles, but also improves the morphology and stability of FAPbBr₃ film. For the top passivation, smaller grains and a FAPbBr₃/PEA₂PbBr₄ 3D/2D hybrid structure are obtained by applying a small amount of PEABr solution. The synergetic interplay of organic/inorganic hybrid ETL and organic halide salt surface modification substantially shrinks the grain size to facilitate radiative recombination, and suppresses non-radiative recombination both at the interface of ETL/perovskite and HTL/perovskite, and in the perovskite layer. As a result, the highly efficient green PeLED sets a new record of device performance for FAPbBr₃-based inverted PeLEDs, with current efficiency of 39.7 cd A^-1, external quantum efficiency of 9.0%, power efficiency of 46.4 lm W^-1, maximum luminance of 6.03 × 10⁴ cd m^-2, and half-lifetime of 297 minutes at an initial brightness of ∼100 cd m^-2.

Surface-Plasmon-Enhanced Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have attracted considerable attention because of their potential in display and lighting applications. To promote commercialization of PeLEDs, it is important to improve the external quantum efficiency of the devices, which depends on their internal quantum efficiency (IQE) and light extraction efficiency. Optical simulations have revealed that 20-50% of the light generated in the device will be lost to surface plasmon (SP) modes formed in the metal/dielectric interfaces. Therefore, extracting the optical energy in SP modes to the air will greatly increase the light extraction efficiency of PeLEDs. In addition, the SPs can accelerate radiative recombination of the emitter via near-field effects. Thus, the IQE of a PeLED can also be enhanced by SP manipulation. In this review, first, general concepts of the SPs and how they can enhance the efficiency of LEDs are introduced. Then recent progresses in SP-enhanced emission of perovskite films and LEDs are systematically reviewed. After that, the challenges and opportunities of the SP-enhanced PeLEDs are shown, followed by an outlook of further development of the SPs in perovskite optoelectronic devices.

Resonant energy transfer and light scattering enhancement of plasmonic random lasers embedded with silver nanoplates

The resonant energy transfer enhancement from a plasmonic random laser (PRL) has been investigated by means of a dye-covered PVA film with embedded silver nanoplates (DC-PVA/AgNPs). Different sizes and morphologies of AgNPs were adopted to shift the localized surface plasmon resonance (LSPR) and intensify recurrent light scattering between the AgNPs. For better overlap between surface plasmon resonance and the photoluminescence of fluorescent molecules with appropriately-sized silver nanoprisms, the slope efficiency of the PRL was greatly enhanced and the lasing threshold was obviously reduced. In addition, the photon lifetime for the DC-PVA/AgNPs film reveals an apparent decline around 1.39 ns owing to better coupling with LSPR. The stronger light scattering of samples with bigger-sized silver nanoprisms has been demonstrated by coherent back scattering measurements, which reveals a smaller transport mean free path around 3.3 μm. With α-stable analysis, it has been successfully demonstrated that the tail exponent α can be regarded as an identifier of the threshold of random lasing.

The resonant energy transfer enhancement from a plasmonic random laser has been investigated by means of a dye-covered PVA film embedded with silver nanoplates with different sizes and morphologies.

Tailoring the electroluminescence of a single microwire based heterojunction diode using Ag nanowires deposition

A single Ga-doped ZnO microwire covered by Ag nanowires (AgNWs@ZnO:Ga MW) was utilized to construct a promising ultraviolet light source, with p-GaN serving as a hole injection layer.

Synergistic Enhancement Effect for Boosting Raman Detection Sensitivity of Antibiotics

In this paper, a two-step method is used to prepare a regenerative three-dimensional (3D) ZnO/Ag@Au substrate for developing a superior sensitive surface enhanced Raman scattering (SERS) method for detecting antibiotics. A great electromagnetic enhancement is observed from the as-prepared composite substrate, which is triggered by tuning the electron distribution of metals and semiconductor metal oxide. The strong interaction between target sample and the huge surface area of ZnO/Ag@Au composite promotes the charge transfer to produce promising chemical enhancement. The synergistic physical and chemical enhancement mechanisms are validated by density functional theory and finite difference time domain simulation. Additionally, the presence of light "echo effect" in the 3D structure of ZnO support could also amplify the efficiency of light excitation for Raman scattering. The above-stated merits benefit to boost the Raman scattering detection sensitivity for real samples. The ZnO/Ag@Au-based SERS substrate could detect rhodamine 6G molecules with an enhancement factor of up to 1.48 × 10⁹ and the lowest detectable concentration of 10^-10 M. As a real application, antibiotics sulfapyridine in milk is determined by using the proposed SERS protocol, and the limit of detection at 1 × 10^-9 M could be reached. As a prospective, the ZnO/Ag@Au-based SERS method would be extended for food safety and biomedicine analysis.

Strategies to Improve Luminescence Efficiency of Metal-Halide Perovskites and Light-Emitting Diodes

Metal-halide perovskites (MHPs) are well suited to be vivid natural color emitters due to their superior optical and electrical properties, such as narrow emission linewidths, easily and widely tunable emission wavelengths, low material cost, and high charge carrier mobility. Since the first development of MHP light-emitting diodes (PeLEDs) in 2014, many researchers have tried to understand the properties of MHP emitters and the limitations to luminescence efficiency (LE) of PeLEDs, and have devoted efforts to increase the LE of MHP emitters and PeLEDs. Within three and half years, PeLEDs have shown rapidly increased LE from external quantum efficiency ≈0.1% to ≈14.36%. Herein, the factors that limit the LE of PeLEDs are reviewed; the factors are characterized into the following groups: i) photophysical properties of MHP crystals, ii) morphological factors of MHP layers, and iii) problems caused by device architectures. Then, the strategies to overcome those luminescence-limiting factors in MHP emitters and PeLEDs are critically evaluated. Finally, research directions to further increase the LE of MHP emitters and the potential of MHPs as a core component in next-generation displays and solid-state lightings are suggested.

PEDOT:PSS for Flexible and Stretchable Electronics: Modifications, Strategies, and Applications

Substantial effort has been devoted to both scientific and technological developments of wearable, flexible, semitransparent, and sensing electronics (e.g., organic/perovskite photovoltaics, organic thin-film transistors, and medical sensors) in the past decade. The key to realizing those functionalities is essentially the fabrication of conductive electrodes with desirable mechanical properties. Conductive polymers (CPs) of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) have emerged to be the most promising flexible electrode materials over rigid metallic oxides and play a critical role in these unprecedented devices as transparent electrodes, hole transport layers, interconnectors, electroactive layers, or motion-sensing conductors. Here, the current status of research on PEDOT:PSS is summarized including various approaches to boosting the electrical conductivity and mechanical compliance and stability, directly linked to the underlying mechanism of the performance enhancements. Along with the basic principles, the most cutting edge-progresses in devices with PEDOT:PSS are highlighted. Meanwhile, the advantages and plausible problems of the CPs and as-fabricated devices are pointed out. Finally, new perspectives are given for CP modifications and device fabrications. This work stresses the importance of developing CP films and reveals their critical role in the evolution of these next-generation devices featuring wearable, deformable, printable, ultrathin, and see-through characteristics.

Emission Editing in Eu/Tb binary complexes based on Au@SiO2 nanorods

The Au@SiO₂ nanorods with two plasmonic resonance bands are used to enhance and tune the emission of binary lanthanide (Eu/Tb) complexes. The emissions of Tb and Eu ions are both enhanced, the maximum enhancement is over 100-fold. Meanwhile the ratio and relative intensity of the red/green bands is altered by the strong coupling between complexes and nanorods, tuning the color of emission from green to yellow under excitation of 292 nm and improving the color purity from orange to red under excitation of 360 nm. The underlying physics of the lanthanide complex-plasmonic nanorod composite system is analyzed, which deepen the understanding of the interaction between complexes and plasmon nanoparticles.

Enhancing the performance of perovskite light-emitting devices through 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene interlayer incorporation

Interface engineering is important for enhancing the luminance efficiency and stability of perovskite light-emitting devices. In this work, we study the effects of spin-coated 1,3,5-tris(2-N-phenylbenzimidazolyl)benzene (TPBi) layer incorporation on the crystal structure, morphology, photo-physics, and charge transport characteristics of the underlying MAPbBr3 layer. Introduction of such a TPBi interlayer effectively reduces defect density and increases radiative recombination in the MAPbBr3 layer. Related perovskite light-emitting devices with a TPBi interlayer show a maximum external quantum efficiency of 9.9% and power efficiency of 22.1 lm W-1, which are 2.0 and 1.6 times those of the devices without a TPBi interlayer, respectively. The study provides a simple and effective method to enhance the performance of perovskite light-emitting devices.

Enhanced electron transportation of PF-NR2 cathode interface by gold nanoparticles

In order to achieve a wider organic light-emitting diode (OLED) commercial popularity, solution processing inverted polymer light-emitting diode (iPLED) is a trend for further development, but there is still a gap for solution processing devices to achieve commercialization. The improvement of the performance iPLEDs is a research topic of intense current interest. The modification of the cathode interface layer of poly[(9,9-bis(3'-(N,N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PF-NR₂) can greatly improve the performance of the devices. However, the electron transportation of the cathode interface layer of PF-NR₂ films is currently poor, and there is substantial interest in improving its electron transportation to further enhance the performance of organic optoelectronic devices. In this paper, gold nanoparticles (Au NPs) with a particle size of 20 nm were prepared and doped into the interface layer PF-NR₂ at a specified ratio. The electron transportation of the interface layer of PF-NR₂ was greatly improved, as judged by conductive atomic force microscopy measurements, which is due to the excellent conductivity of Au NPs. Herein, we demonstrate improved electron transportation of the interface layer by doping Au NPs in PF-NR₂ film, which provides important and practical theoretical guidance and technical support for the preparation of high performance organic optoelectronic devices.

Self-template Synthesis of Metal Halide Perovskite Nanotubes as Functional Cavities for Tailored Optoelectronic Devices

Intriguing optoelectronic features of low-dimensional perovskites drive researchers to develop novel nanostructures for exploring new photophysical properties and meeting the requirements of future practical applications. Here, we report the facile and universal synthesis of metal halide perovskite nanotubes (NTs) in a micro alkylammonium emulsion system for the first time. The [PbBr₆]^4--based NTs with a diameter of 300 nm and length of 100 μm were synthesized through the reaction of PbBr₂ and long-chain bromide in advance, which can be controllably converted into general metal halide perovskite APbBr₃ (A = Cs, FA, MA) with preserved tubular morphology by introducing the Cs⁺, MA⁺, and FA⁺ cations. Importantly, the NTs can readily couple with other nanofillers exhibiting tunable and novel optoelectronic properties demonstrated by the photodetectors. The device performance can be significantly improved and broadened to infrared photoresponse through the introduction of Au nanocrystal (NC) plasma and PbS NCs, respectively. These results demonstrate that the metal halide perovskite NTs are expected to enrich the diversity of nanostructures and have a huge potential in the fabrication of integrated, light-manipulated, and miniaturized electronic and photonic devices.

Effects of n-butyl amine incorporation on the performance of perovskite light emitting diodes

The efficiency of perovskite light emitting diodes (PeLEDs) is crucially limited by leakage current and nonradiative recombination. Here we introduce n-butyl amine (BA) to modulate the growth of perovskite films as well as improve the performance of PeLEDs, and investigate in detail the effects of BA incorporation on the structural, optical, and electrical characteristics of perovskite films. The results indicate that BA would terminate the grain surface and inhibit crystal growth, leading to increased radiative recombination. However, BA overload would make the films loose and recreate shunt paths. The electrical detriment of BA overload outweighs its optical benefit. As a result, optimal PeLEDs can be obtained only with moderate BA incorporation.

All-Solution-Processed Pure Formamidinium-Based Perovskite Light-Emitting Diodes

All-solution-processed pure formamidinium-based perovskite light-emitting diodes (PeLEDs) with record performance are successfully realized. It is found that the FAPbBr₃ device is hole dominant. To achieve charge carrier balance, on the anode side, PEDOT:PSS 8000 is employed as the hole injection layer, replacing PEDOT:PSS 4083 to suppress the hole current. On the cathode side, the solution-processed ZnO nanoparticle (NP) is used as the electron injection layer in regular PeLEDs to improve the electron current. With the smallest ZnO NPs (2.9 nm) as electron injection layer (EIL), the solution-processed PeLED exhibits a highest forward viewing power efficiency of 22.3 lm W^-1 , a peak current efficiency of 21.3 cd A^-1 , and an external quantum efficiency of 4.66%. The maximum brightness reaches a record 1.09 × 10⁵ cd m^-2 . A record lifetime T₅₀ of 436 s is achieved at the initial brightness of 10 000 cd m^-2 . Not only do PEDOT:PSS 8000 HIL and ZnO NPs EIL modulate the injected charge carriers to reach charge balance, but also they prevent the exciton quenching at the interface between the charge injection layer and the light emission layer. The subbandgap turn-on voltage is attributed to Auger-assisted energy up-conversion process.

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

The development of smart illumination sources represents a central challenge for current technology. In this context, the quest for novel materials that enable efficient light generation is essential. Metal halide compounds with perovskite crystalline structure (ABX₃) have gained tremendous interest in the last five years since they come as easy-to-prepare high performance semiconductors. Perovskite absorbers are driving the power-conversion-efficiencies of thin film photovoltaics to unprecedented values. Nowadays, mixed-cation, mixed-halide lead perovskite solar cells reach efficiencies consistently over 20% and promise to get close to 30% in multijunction devices when combined with silicon cells at no surcharge. Nonetheless, perovskites' fame extends further since extensive research on these novel semiconductors has also revealed their brightest side. Soon after their irruption in the photovoltaic scenario, demonstration of efficient color tunable-with high color purity-perovskite emitters has opened new avenues for light generation applications that are timely to discuss herein.

Extra thermo- and water-stable one-dimensional organic-inorganic hybrid perovskite [N-methyldabconium]PbI3 showing switchable dielectric behaviour, conductivity and bright yellow-green emission

Haloplumbate-based perovskites display promising functionalities for advanced photovoltaic, optoelectronic and other applications with high performances and low costs. Herein, we present a study of variable-temperature crystal structures, dielectrics and conductance at 153-513 K, and luminescence at ambient temperature for a one-dimensional organic-inorganic perovskite, [N-methyldabconium]PbI3 (1). Hybrid 1 shows extra thermo- and water-stability (thermal decomposition at ca. 653 K), switchable dielectric behaviour and conductance at around 348 K, owing to symmetry-breaking structure phase transition from the hexagonal space group P63/mmc in the high-temperature phase to the orthogonal space group Pcba in the low-temperature phase, and bright yellow-green emission at room temperature, originating from the electron transition within the semiconducting {PbI3}∞ chains. This study will broaden the scope of lead halide-based hybrid materials for practical application in optical and electrical devices.

Electrode quenching control for highly efficient CsPbBr3 perovskite light-emitting diodes via surface plasmon resonance and enhanced hole injection by Au nanoparticles

Compared to organic-inorganic hybrid metal halide perovskites, all-inorganic cesium lead halides (e.g, CsPbBr₃) hold greater promise in being emissive materials for light-emitting diodes owing to their superior optoelectronic properties as well as their higher stabilities. However, there is still considerable potential for breakthroughs in the current efficiency of CsPbBr₃ perovskite light-emitting diodes (PeLEDs). Electrode quenching is one of the main problems limiting the current efficiency of PeLEDs when poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS) is used as the hole injection layer. In this work, electrode quenching control was realized via incorporating Au NPs into PEDOT:PSS. As a result, the CsPbBr₃ PeLEDs realized an improvement in maximum luminescence ranging from ∼2348 to ∼7660 cd m^-2 (∼226% enhancement) and current efficiency from 1.65 to 3.08 cd A^-1 (∼86% enhancement). Such substantial enhancement of the electroluminescent performance can be attributed to effective electrode quenching control at the PEDOT:PSS/CsPbBr₃ perovskite interface via the combined effects of local surface plasma resonance coupling and enhanced hole transportation in the PEDOT:PSS layer by Au nanoparticles.

Interfacial engineering with ultrathin poly (9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) layer for high efficient perovskite light-emitting diodes

Organic-inorganic hybrid perovskites have attracted great attention in the field of lighting and display due to their very high color purity and low-cost solution-process. Researchers have done a lot of work in realizing high performance electroluminescent devices. However, the current efficiency (CE) of methyl-ammonium lead halide perovskite light-emitting diodes (PeLEDs) still needs to be improved. Herein, we demonstrate the enhanced performance of PeLEDs through introducing an ultrathin poly(9,9-di-n-octylfluorenyl-2,7-diyl) (PFO) buffer layer between poly(3,4-ethylendioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and CH₃NH₃PbBr₃ perovskite. Compared to the reference device without PFO, the optimal device luminous intensity, the maximum CE, and the maximum external quantum efficiency increases from 8139 cd m^-2 to 30 150 cd m^-2, from 7.20 cd A^-1 (at 6.8 V) to 10.05 cd A^-1 (at 6.6 V), and from 1.73% to 2.44%, respectively. The ultrathin PFO layer not only reduces the exciton quenching at the interface between the hole-transport layer and emission layer, but also passivates the shallow-trap ensure increasing hole injection, as well as increases the coverage of perovskite film.