Enhancing Light Outcoupling Efficiency via Anisotropic Low Refractive Index Electron Transporting Materials for Efficient Perovskite Light-Emitting Diodes

Efficient and Super-Stable 990 Nm Light‑Emitting Diodes Based on Quantum Cutting Emission of Trivalent Ytterbium in Pure-Br Quasi‑2D Perovskites

Quasi 2D layered metal halide perovskites (2D-LMHPs) with natural quantum wells (QWs) structure have garnered significant attention due to their excellent optoelectronic properties. Doping rare earth (RE) ions with 4fn inner shell emission levels can largely expand their optical and optoelectronic properties and realize diverse applications, but has not been reported yet. Herein, an efficient Yb3+-doped PEA2Cs2Pb3Br10 quasi 2D-LMHPs is fabricated and directly identified the Yb3+ ions in the quasi 2D-LMHPs at the atomic scale using aberration electron microscopy. The interaction between different n phases and Yb3+ ions is elucidated using ultrafast transient absorption spectroscopy and luminescent dynamics, which demonstrated efficient, different time scales and multi-channel energy transfer processes. Finally, through phase distribution manipulation and surface passivation, the optimized film exhibits a photoluminescence quantum yield of 144%. This is the first demonstration of quantum cutting emission in pure Br-based perovskite material, suppressing defect states and ion migration. The efficient and stable near-infrared light-emitting diodes (NIR LED) is fabricated with a peak external quantum efficiency (EQE) of 8.8% at 990 nm and the record lifetime of 1274 min. This work provides fresh insight into the interaction between RE ions and quasi 2D-LMHPs and extend the function and application of quasi 2D-LMHPs materials.

Efficient and stable blue perovskite light-emitting diodes enabled by the synergistic incorporation of dual additives

Perovskite materials have garnered significant attention in the field of light-emitting diodes (LEDs) due to their low cost, solution processing, straightforward fabrication, tunable emission wavelengths, narrow emission linewidths, and high photoluminescence quantum yield. However, blue perovskite light-emitting diodes (PeLEDs) currently face challenges of low efficiency and poor stability, which hinder their application in full-color display technology. It is understood that the quality of the perovskite film is considered a key factor affecting the performance of PeLEDs. To achieve high-quality perovskite films and high-performance PeLEDs, benzoic acid potassium (BAP) and guanidinium chloride (GACl) were employed as dual additives in the precursor solution of a quasi-two-dimensional perovskite (PEA2Csn-1PbnX3n+1). By utilizing the coordination of BA- from BAP with uncoordinated Pb2+ and the formation of hydrogen bonds between GA+ from GACl and halide ions, the perovskite surface defects are effectively passivated, along with the inhibition of the migration of halide ions. This approach reduces non-radiative recombination and enhances the spectral stability of perovskite films. By fine-tuning the concentrations of BAP and GACl, optimal PeLEDs are achieved at a BAP concentration of 3% and a GACl concentration of 10%, with the spectrum stabilized at 476 nm and a maximum external quantum efficiency (EQEmax) of 4.47%, which is 2.54 times that of the control device (EQEmax of 1.76%). The findings in this study provide a new approach for the fabrication of highly efficient and spectrally stable blue PeLEDs.

Efficient Blue Perovskite LEDs via Bottom-Up Charge Manipulation for Solution-Processed Active-Matrix Displays

Perovskite light-emitting diodes (PeLEDs) are emerging as strong candidates for next-generation displays due to their outstanding optoelectronic properties, solution processability, and cost-effectiveness. However, the development of highly efficient blue PeLEDs remains a significant challenge. Here, a bottom-up strategy is introduced for precise charge manipulation in blue perovskites to enhance radiative recombination efficiency. By employing 1,3-bis(N-carbazolyl)benzene as an inserted hole transport layer, improved hole injection efficiency is achieved while effectively suppressing reverse electron transport and exciton quenching. Additionally, a fluorinated ester additive is incorporated to control perovskite crystallization, facilitating the formation of well-aligned reduced-dimensional phases to reduce nonradiative recombination losses. The resulting blue PeLEDs exhibit a record-breaking external quantum efficiency of 25.87%, the highest reported for one-step-prepared blue perovskite films. Furthermore, integration with thin-film transistor circuits enables solution-processed active-matrix perovskite displays with sharp and uniform patterning. This work provides a comprehensive pathway for advancing blue PeLEDs toward high-performance display applications.

Mitigation of Nonradiative Recombination by Reconfiguring Triplet Energy of Additive Toward Efficient Blue Perovskite Light-Emitting Diodes

The exceptional optoelectronic properties of metal halide perovskites, including enhanced color saturation and tunable emission wavelengths, render them highly potential candidates for fabricating perovskite light-emitting diodes (PeLEDs). However, blue PeLEDs underperform relative to their red and green counterparts due to substantial nonradiative recombination losses, particularly at the perovskite/electron transporting layer (ETL) interface. Here, we propose an effective energy management strategy aimed at boosting the efficiency of blue PeLEDs by the incorporation of a multifunctional interlayer, specifically 2,8-bis(diphenylphosphoryl)dibenzo[b,d]furan (PPF), at the perovskite/ETL interface. This approach involves the formation of robust P═O/Pb bonds between PPF and perovskite surface defects, thereby effectively mitigating trap-induced nonradiative recombination. Furthermore, the high triplet energy level of PPF inhibits triplet energy transfer from the perovskite to the ETL, leading to further reductions in energy loss. Consequently, the optimized blue PeLEDs exhibit a peak external quantum efficiency (EQE) of 15.1% (peak emission at 472 nm) with a 4-fold increased operational lifetime compared to the control PeLED. Additionally, utilizing blue PeLED units treated with PPF, we achieve a record EQE of 31.1% for hybrid perovskite/organic tandem white LEDs, which exhibit a high color rendering index of 85.

1.5D Chiral Perovskites Mediated by Hydrogen-Bonding Network with Remarkable Spin-Polarized Property

In this study, we developed new chiral hybrid perovskites, (R/S-MBA)(GA)PbI4, by incorporating achiral guanidinium (GA+) and chiral R/S-methylbenzylammonium (R/S-MBA+) into the perovskite framework. The resulting materials possess a distinctive structural configuration, positioned between 1D and 2D perovskites, which we describe as 1.5D. This structure is featured by a hydrogen-bonding-network-induced arrangement of zigzag inorganic chains, further forming an organized layered architecture. The structural dimensionality affects both electronic and spin-related properties. Density functional theory (DFT) calculations reveal Rashba splitting induced by the inversion asymmetry of the crystal structure, while circularly polarized transient absorption spectroscopy confirms spin lifetime on the nanosecond timescale. Magnetic conductive-probe atomic force microscopy (mCP-AFM) measurements demonstrate exceptional chiral-induced spin selectivity (CISS) with maximum spin polarization degrees of (92±1)% and (-94±2)% for (R-MBA)(GA)PbI4 and (S-MBA)(GA)PbI4, respectively. These findings underscore the potential of (R/S-MBA)(GA)PbI4 as promising candidates for next-generation spintronic devices, also highlight the critical role of chemical environment in sculpturing the structural dimension and spin-polarized property of chiral perovskites.

Strategies for Stabilizing Metal Halide Perovskite Light-Emitting Diodes: Bulk and Surface Reconstruction of Perovskite Nanocrystals

Light-emitting colloidal lead halide perovskite nanocrystals (PeNCs) are considered promising candidates for next-generation vivid displays. However, the operational stability of light-emitting diodes (LEDs) based on PeNCs is still lower than those based on polycrystalline perovskite films, which requires an understanding of defect formation in PeNCs, both inside the crystal lattice ("bulk") and at the surface. Meanwhile, uncontrollable ion redistribution and electrochemical reactions under LED operation can be severe, which is also related to the bulk and surface quality of PeNCs, and a well-designed device architecture can boost carrier injection and balance radiative recombination. In this review, we consider bulk and surface reconstruction of PeNCs by enhancing the crystal lattice rigidity and rationally selecting the surface ligands. Degradation pathways of PeNCs under applied voltage are discussed, and strategies are considered to avoid both undesirable ion migration and electrochemical reactions in the PeNC films. Subsequently, other critical issues hindering the commercial application of PeNC LEDs are discussed, including the toxicity of Pb in lead halide perovskites, scale-up deposition of PeNC films, and design of active-matrix prototypes for high-resolution LED modules.

Narrowband emission and enhanced stability in top-emitting OLEDs with dual resonant cavities

Capping layers (CPLs) are commonly employed in top-emitting organic light-emitting diodes (TEOLEDs) due to their ability to optimize color purity, enhance external light out-coupling efficiency, and improve device stability. However, the mismatch in refractive index between CPLs and thin film encapsulation (TFE) often induces light trapping. This study introduces a novel approach by combining a low refractive index material, lithium fluoride (LiF), with the traditional TFE material, silicon nitride (SiNx), to form a combined CPL (LiF/SiNx), resulting in improved light outcoupling and light reflection properties. The significant refractive index contrast between LiF and SiNx can facilitate enhanced light extraction by redirecting internally reflected light through evanescent waves. Moreover, the LiF/SiNx CPLs function as a secondary resonant cavity, leading to reduced emission spectral bandwidth and enhanced light extraction compared to the control TEOLEDs that only incorporate the primary cavity of organic active layers. As a result, incorporating the LiF/SiNx CPLs significantly increases current efficiency from 125.0 cd A-1 to 163.6 cd A-1 for green devices, from 71.2 cd A-1 to 110.1 cd A-1 for red devices, and from 43.1 cd A-1 to 53.1 cd A-1 for blue devices, with the corresponding full width at half maximum decreased from 20 nm to 10 nm, 26 nm to 14 nm, and 21 nm to 12 nm, respectively, demonstrating the compatibility of the CPLs with different color devices. Notably, an LT95 lifetime of 51 300 hours for green devices was achieved when tested at 1000 cd m-2. Utilizing narrow-band light emission without spectral overlap of each color enables the generation of purer and more vivid colors for display.

Blue-Emitting CsPbBr3 Nanocrystals: Synthesis Progress and Bright Photoluminescence

All-inorganic perovskite (CsPbX3, X = Cl, Br, I) nanomaterials as novel optoelectronic semiconductors have attracted much attention due to their unique photoelectric properties in lighting, display, and photovoltaic applications. Meanwhile, green and red light-emitting diodes (LEDs) based on bromine and iodine groups have developed rapidly, in which the high external quantum efficiency (EQE) is close to that of the current commercial green and red LEDs. However, the EQE of perovskite-based blue LEDs is far behind. Blue LEDs are often made by CsPbCl3 and CsPb(Cl/Br)3 nanocrystals (NCs) with low photoluminescence (PL) quantum yields. Their phase segregation seriously limits their practical applications. The PL peak of CsPbBr3 NCs is usually located in the green region. In the case of a strong quantum confinement effect, blue PL can be observed from CsPbBr3 NCs. Therefore, blue emitting CsPbBr3 NCs have become a hot topic. This review focused on the synthesis, ligand selection, and morphology control of blue emitting CsPbBr3 NCs, in which the microstructure, luminescence, and synthesis method were first discussed. In addition, the influence of capping ligands on the PL properties and stability is indicated. Furthermore, the size and morphology adjustment are also discussed. Finally, the application and existing problems of blue-emitting CsPbBr3 in blue LEDs are summarized. This review aims to provide new insights into the preparation of efficient and stable blue-emitting CsPbBr3 and the design-based manufacturing of blue LEDs.

Ultralow trap density FAPbBr3 perovskite films for efficient light-emitting diodes and amplified spontaneous emission

Solution-processed metal halide perovskites are widely studied for their potential in high-efficiency light-emitting diodes, yet they are facing several challenges like insufficient brightness, short operational lifetimes, and reduced power conversion efficiency under practical operation conditions. Here, we develop an interfacial amidation reaction on sacrificial ZnO substrates to produce perovskite films with low trap density (1.2 × 1010 cm-3), and implement a device structure featuring a mono-molecular hole-injection layer and an all-inorganic bi-layered electron-injection layer. This design leads to green perovskite light-emitting diodes with a brightness of ~ 312,000 cd m-2, a half-lifetime of 350 h at 1000 cd m-2, and a power conversion efficiency of 15.6% at a current density of 300 mA cm-2. Furthermore, the perovskite films show a low amplified spontaneous emission threshold of 13 μJ cm-2. Thus, our approach significantly advances the performance of green perovskite light-emitting diodes and opens up an avenue toward perovskite-based electrically pumped lasers.

Research Advances in Ion Exchange of Halide Perovskites

In recent years, halide perovskite materials have been extensively studied by researchers due to their excellent optoelectronic characteristics. Unlike traditional semiconductors, halide perovskites possess unique ionic crystal structures, which makes it easier to perform facile composition engineering to tailor their physical and chemical properties. Ion exchange is a popular post-treatment strategy to achieve composition engineering in perovskites, and various ion exchange processes have been used to modify the structural and functional features of prefabricated perovskites to meet the requirements of desired applications. This review summarizes the recent progress in ion exchange of halide perovskites, including mechanisms, strategies, and studies on different ion exchange. Additionally, the applications of ion-exchanged perovskites in microfluidic sensors, light-emitting diodes (LEDs), lasers, and solar cells are presented. Lastly, we briefly discuss the challenges in ion exchange of perovskites and hope that ion exchange can provide a more refined and reliable method for the preparation of high-performance perovskites.

Manipulation of Metal Halide Perovskite: Photoelectric Conversion or Light Emission?

Metal halide perovskites (MHPs) display a range of superior photophysical properties, rendering them promising as a candidate for the active medium of high-efficiency photovoltaic and electroluminescence devices. In order to maximize their efficacy in photoelectric conversion or light emission, it is essential to regulate the charge separation efficiency of MHPs in a desired manner. Herein, we demonstrate that the extent of charge separation can be effectively manipulated upon thermal annealing treatment on MHPs. As the annealing time is extended from 10 to 30 min, the accumulation of excess lead halides is observed at the boundaries of MHP grains, resulting in the construction of a quasi-Type II band alignment between the lead halide and the MHP. This facilitates the separation of electron-hole pairs, reducing the exciton binding energy from approximately 102 meV to a level comparable with kBT. Our findings elucidate the transition of MHPs from a light-emission material to a photoelectric-conversion material along with continuous heating treatment, which is anticipated to guide the flexible regulation of MHPs to meet the requirements of specific practical applications.

Nanocrystalline Perovskites for Bright and Efficient Light-Emitting Diodes

Nanocrystalline perovskites have driven significant progress in metal halide perovskite light-emitting diodes (PeLEDs) over the past decade by enabling the spatial confinement of excitons. Consequently, three primary categories of nanocrystalline perovskites have emerged: nanoscale polycrystalline perovskites, quasi-2D perovskites, and perovskite nanocrystals. Each type has been developed to address specific challenges and enhance the efficiency and stability of PeLEDs. This review explores the representative material design strategies for these nanocrystalline perovskites, correlating them with exciton recombination dynamics and optical/electrical properties. Additionally, it summarizes the trends in progress over the past decade, outlining four distinct phases of nanocrystalline perovskite development. Lastly, this review addresses the remaining challenges and proposes a potential material design to further advance PeLED technology toward commercialization.

Efficient perovskite LEDs with tailored atomic layer number emission at fixed wavelengths

Colloidal quantum dots (QDs) have illuminated computer monitors and television screens due to their fascinating color-tunable properties depending on the size. Here, the electroluminescence (EL) wavelength of perovskite LEDs was tuned via the atomic layer number (ALN) of nanoplates (NPs) instead of the "size" in conventional QDs. We demonstrated efficient LEDs with controllably tailored emission from n = 3, 4, 5, and ≥7 ALN perovskite NPs with specific and discrete major peaks at 607, 638, 669, and 728 nanometers. These LEDs demonstrated peak external quantum efficiency (EQE) of 26.8% and high wavelength reproducibility with less than 1 to 2 nm difference between batches. High color stability without observable EL spectral change and operating stability with the best T50 of 267 minutes at 1.0 milliampere per square centimeter was also achieved. This work demonstrates a concept of tailoring specific ALN emission with fixed wavelengths, shedding light on efficient, emission-discrete, and color-stable LEDs for next-generation display.

A review: strategies for reducing the open-circuit voltage loss of wide-bandgap perovskite solar cells

Perovskite-based tandem solar cells (PTSCs) have made remarkable achievements in recent years, and the highest certified power conversion efficiency (PCE) of 33.9% has been achieved in perovskite/silicon tandem solar cells (PSTSCs), indicating their great commercialization potential. Nevertheless, the performance of PTSCs continues to be hindered by the compromised performance of wide-bandgap perovskite solar cells (WPSCs), particularly the high VOC deficit of WPSCs. Therefore, numerous strategies have been developed to minimize the VOC loss of WPSCs. Herein, we sort to comprehensively review about the reported studies on reducing the VOC deficit of WPSCs, focusing on interface modification, charge transport material (CTM) exploration, and additive engineering, with the aim of providing guidelines for increasing the VOC of WPSCs. Finally, we will provide a conclusive outlook on WPSCs, sharing our perspectives to inspire further advancements in both WPSCs and PTSCs.

Screening Fluorination Additives for Efficient Perovskite Light-Emitting Diodes

Fluorinated additives are proposed to address the issue of domain polydispersity in quasi-2D perovskites. However, the lack of established screening criteria for these additives necessitates a laborious and costly trial-and-error process. Herein, this work explores the behind nature for the first time how various fluorination in fluorinated additives affect domain distribution in quasi-2D perovskites. The studies reveal that fully fluorinated additives could suppress undesirable low-dimensional domains, facilitating efficient energy transfer, while partially fluorinated additives adversely cause deteriorated optical properties. The observed trend is ascribed to the molecular dipole moment of the fluorinated additives, offering a reasonable explanation for experimental phenomena that has never been reported before. By employing fully fluorinated additives, the fabricated sky-blue perovskite light-emitting diodes (PeLEDs) deliver a peak external quantum efficiency (EQE) of 20.38% (@488 nm), marking as one of the highest efficiencies reported to date. The finding provides a screening criterion for fluorinated additives to realize efficient PeLEDs.

Wide-Bandgap Lead Halide Perovskites for Next-Generation Optoelectronics: Current Status and Future Prospects

Over the past decade, lead halide perovskites (LHPs), an emerging class of organic-inorganic ionic-type semiconductors, have drawn worldwide attention, which injects vitality into next-generation optoelectronics. Facilely tunable bandgap is one of the fascinating features of LHPs, enabling them to be widely used in various nano/microscale applications. Notably, wide-bandgap (WBG) LHPs have been considered as promising alternatives to traditional WBG semiconductors owing to the merits of low-cost, solution processability, superior optoelectronic characteristics, and flexibility, which could improve the cost-effectiveness and expand the application scenarios of traditional WBG devices. Herein, we provide a comprehensive review on the up-to-date research progress of WBG LHPs and their optoelectronics in terms of material fundamentals, optoelectronic devices, and their practical applications. First, the features and shortcomings of WBG LHPs are introduced to objectively display their natural features. Then we separately depict three typical optoelectronic devices based on WBG LHPs, including solar cells, light emitting diodes, and photodetectors. Sequentially, the inspiring applications of these optoelectronic devices in integrated functional systems are elaborately demonstrated. At last, the remaining challenges and future promise of WBG LHPs in optoelectronic applications are discussed. This review highlights the significance of WGB LHPs for promoting the development of the next-generation optoelectronics industry.

Strategies for Controlling Emission Anisotropy in Lead Halide Perovskite Emitters for LED Outcoupling Enhancement

In the last decade, momentous progress in lead halide perovskite (LHP) light-emitting diodes (LEDs) is witnessed as their external quantum efficiency (ηext) has increased from 0.1 to more than 30%. Indeed, perovskite LEDs (PeLEDs), which can in principle reach 100% internal quantum efficiency as they are not limited by the spin-statistics, are reaching their full potential and approaching the theoretical limit in terms of device efficiency. However, ≈70% to 85% of total generated photons are trapped within the devices through the dissipation pathways of the substrate, waveguide, and evanescent modes. To this end, numerous extrinsic and intrinsic light-outcoupling strategies are studied to enhance light-outcoupling efficiency (ηout). At the outset, various external and internal light outcoupling techniques are reviewed with specific emphasis on emission anisotropy and its role on ηout. In particular, the device ηext can be enhanced by up to 50%, taking advantage of the increased probability for photons outcoupled to air by effectively inducing horizontally oriented emission transition dipole moments (TDM) in the perovskite emitters. The role of the TDM orientation in PeLED performance and the factors allowing its rational manipulation are reviewed extensively. Furthermore, this account presents an in-depth discussion about the effects of the self-assembly of LHP colloidal nanocrystals (NCs) into superlattices on the NC emission anisotropy and optical properties.

Metal Halide Perovskite LEDs for Visible Light Communication and Lasing Applications

Metal halide perovskites, known for their pure and tunable light emission, near-unity photoluminescence quantum yields, favorable charge transport properties, and excellent solution processability, have emerged as promising materials for large-area, high-performance light-emitting diodes (LEDs). Over the past decade, significant advancements have been made in enhancing the efficiency, response speed, and operational stability of perovskite LEDs. These promising developments pave the way for a broad spectrum of applications extending beyond traditional solid-state lighting and displays to include visible light communication (VLC) and lasing applications. This perspective evaluates the current state of perovskite LEDs in those emerging areas, addresses the primary challenges currently impeding the development of perovskite-based VLC systems and laser diodes, and provides an optimistic outlook on the future realization of perovskite-based VLC and electrically pumped perovskite lasers.

Manipulating Electron-Phonon Coupling for Efficient Tin Halide Perovskite Blue LEDs

Low-dimensional perovskites have opened up a new frontier in light-emitting diodes (LED) due to their excellent properties. However, concerns regarding the potential toxicity of Pb limited their commercial development. Sn-based perovskites are regarded as a promising candidate to replace Pb-based counterparts, while they generally exhibit strong electron-phonon coupling and consequently blue emission quenching at room temperature (RT), thus the Sn-based perovskite blue LED devices have not yet been reported. Herein, the luminescence properties are regulated by assembling a rigid organic skeleton within perovskite structure, and the protonated 4-bromobenzylamine (BrPMA+ = C7H9BrN+) is employed as A site cation to synthesize a 100-oriented 2D perovskite (BrPMA)2SnBr4, which exhibits a strong lattice rigidity via strong intermolecular interaction and consequently weak electron-phonon coupling, achieving the excellent blue PL emission at RT. The high quality (BrPMA)2SnBr4 perovskite thin films are obtained by further inhibiting oxidation and promoting crystallization. Finally, the Sn-based perovskite blue emission LED is successfully fabricated for the first time at 467 nm with a champion EQE of 1.3% and a maximum brightness of 800 cd m-2. This work gives insights into the luminescence mechanism of Sn-based perovskites and provides a new theoretical basis for the development of lead-free blue LEDs.

Optimizing Perovskite Surfaces to Enhance Post-Treatment for Efficient Blue Mixed-Halide Perovskite Light-emitting Diodes

The halide postdeposition treatment technique is a widely used strategy for mitigating defects in perovskite. However, when applied to mixed-halide perovskites, it often leads to surface and internal halide heterogeneity, which compromises luminescence performance and spectral stability. In this work, blue mixed-halide 3D perovskites are engineered with acetate (Ac⁻)-rich surfaces to optimize the post-treatment process and achieve halide homogeneity. The findings demonstrate that the strong interaction between surface Ac⁻ ions and Pb2+ ions significantly reduces the formation of halide vacancy defects caused by the washing effect of isopropanol during post-treatment. This defect reduction slows the infiltration of halide ions into the perovskite lattice, providing more time for surface reconstruction and minimizing the accumulation of introduced halide ions at the surface. As a result, a mild halide redistribution occurs, promoting the formation of a uniform mixed-halide perovskite phase. This approach enabled the development of blue mixed-halide 3D PeLEDs with a record external quantum efficiency of 19.28% (emission peak at 482 nm), comparable to state-of-the-art blue reduced-dimensional perovskite-based PeLEDs. Additionally, the device demonstrated a narrowband and stable electroluminescence spectrum with a full width at half maximum (FWHM) of less than 16 nm.

The Rise of Tandem Perovskite Light-Emitting Diode

In 2024, tandem perovskite light-emitting diodes (tandem-PLEDs) achieved a breakthrough external quantum efficiency of 43.42%, with an organic electroluminescence (EL) unit stacked atop a perovskite EL unit, surpassing the previous single-junction perovskite LEDs. This innovative design enables a higher brightness at lower currents, enhancing the longevity and efficiency of the tandem-PLEDs. Additionally, the tandem-PLEDs can also be fabricated by combining a perovskite EL unit with a perovskite quantum dot unit. In this perspective, the key advancements in tandem-PLEDs are highlighted, focusing on the development of perovskite-organic materials, perovskite-perovskite quantum dots, and the design principles for obtaining efficient and stable charge generation layers. But more importantly, the challenges and solutions are discussed in fabricating all-perovskite tandem LEDs using strongly polar solvents that have yet to be reported nowadays. This comprehensive guide aims to support researchers in advancing the practical deployment of tandem-PLED technology.

Spontaneous Cooling Enables High-Quality Perovskite Wafers for High-Sensitivity X-Ray Detectors with a Low-Detection Limit

Developing high-quality perovskite wafers is essential for integrating perovskite technology throughout the chip industry chain. In this article, a spontaneous cooling strategy with a hot-pressing technique is presented to develop high-purity, wafer-scale, pinhole-free perovskite wafers with a reflective surface. This method can be extended to a variety of perovskite wafers, including organic-inorganic, 2D, and lead-free perovskites. Besides, the size of the wafer with diameters of 10, 15, and 20 mm can be tailored by changing the mold. Furthermore, the mechanism of spontaneous cooling for improving the quality of perovskite wafers is revealed. Finally, the high-quality lead-free Cs3Cu2I5 perovskite wafers demonstrate excellent X-ray detection performances with a high sensitivity of 3433.6 µC Gyair -1 cm-2 and a low detection limit of 33.17 nGyair s-1. Moreover, the Cs3Cu2I5 wafers exhibit outstanding environmental and operational stability even without encapsulation. These research presents a spontaneous cooling strategy to achieve wafer-scale, high-quality perovskites with mirror-like surfaces for X-ray detection, paving the way for integrating perovskites into electronic and optoelectronic devices and promoting the practical application of perovskite X-ray detectors.

Cascade Effect of a Dimerized Thermally Activated Delayed Fluorescence Dendrimer

Thermally activated delayed fluorescence (TADF) emitters with a high horizontal orientation are highly essential for improving the external quantum efficiency (EQE) of organic light-emitting diodes; however, pivotal molecular design strategies to improve the horizontal orientation of solution-processable TADF emitters are still scarce and challenging. Herein, a phenyl bridge is adopted to connect the double TADF units, and generate a dimerized TADF dendrimer, D4CzBNPh-SF. Compared to its counterpart with a single TADF unit, the proof-of-the-concept molecule not only exhibits an improved horizontal dipole ratio (78 %) due to the π-delocalization-induced extended molecular conjugation, but also displays a faster reversed intersystem crossing rate constant (6.08×106 s-1) and a high photoluminescence quantum yield of 95 % in neat film. Consequently, the non-doped solution-processed device with D4CzBNPh-SF as the emitter achieves an ultra-high maximum EQE of 32.6 %, which remains at 26.6 % under a luminance of 1000 cd/m2. Furthermore, when using D4CzBNPh-SF as a sensitizer, the TADF-sensitized fluorescence device exhibits a high maximum EQE of 30.7 % at a luminance of 575 cd/m2 and a full width at half maximum of 36 nm.

Surficial Homogenic Effect Enables Highly Stable Deep-Blue Perovskite Light-Emitting Diodes

The device performance of deep-blue perovskite light-emitting diodes (PeLEDs) is primarily constrained by low external quantum efficiency (EQE) especially poor operational stability. Herein, we develop a facile strategy to improve deep-blue emission through rational interface engineering. We innovatively reported the novel electron transport material, 4,6-Tris(4-(diphenylphosphoryl)phenyl)-1,3,5-triazine (P-POT2T), and utilized a sequential wet-dry deposition method to form the homogenic gradient interface between electron transport layer (ETL) and perovskite surface. Unlike previous reports that achieved carrier injection balance by inserting new interlayers, our strategy not only passivated uncoordinated Pb2+ in the perovskite via P=O functional groups but also reduced interfacial carrier recombination without introducing new interfaces. Additionally, this strategy enhanced the interface contact between the perovskite and ETL, significantly boosting device stability. Consequently, the fabricated deep-blue PeLEDs delivered an EQE exceeding 5 % (@ 460 nm) with an exceptional halftime extended to 31.3 minutes. This straightforward approach offers a new strategy to realize highly efficient especially stable PeLEDs.

Homogenizing Energy Landscape for Efficient and Spectrally Stable Blue Perovskite Light-Emitting Diodes

Blue perovskite light-emitting diodes (PeLEDs) have attracted enormous attention; however, their unsatisfactory device efficiency and spectral stability still remain great challenges. Unfavorable low-dimensional phase distribution and defects with deeper energy levels usually cause energy disorder, substantially limiting the device's performance. Here, an additive-interface optimization strategy is reported to tackle these issues, thus realizing efficient and spectrally stable blue PeLEDs. A new type of additive-formamidinium tetrafluorosuccinate (FATFSA) is introduced into the quasi-2D mixed halide perovskite accompanied by interface engineering, which effectively impedes the formation of undesired low-dimensional phases with various bandgaps throughout the entire film, thereby boosting energy transfer process for accelerating radiative recombination; this strategy also diminishes the halide vacancies especially chloride-related defects with deep energy level, thus reducing nonradiative energy loss for efficient radiative recombination. Benefitting from homogenized energy landscape throughout the entire perovskite emitting layer, PeLEDs with spectrally-stable blue emission (478 nm) and champion external quantum efficiency (EQE) of 21.9% are realized, which represents a record value among this type of PeLEDs in the pure blue region.

Bidirectional Inhibiting Interfacial Ion Migration in the Inorganic Hole Transport Layer for Perovskite Light-Emitting Diodes

Cu2ZnSnS4 (CZTS) is strong candidate for hole transport in perovskite light emitting diodes (PeLEDs) due to their cost-effectiveness, deep highest occupied molecular orbital (HOMO), and high hole mobility. However, its inherent polymetallic ions usually deteriorate the quality of the perovskite emission layer (EML) affecting device performance. In this study, a bidirectional anchoring strategy is proposed by adding 15-crown-5 ether (15C5) into CZTS hole transport layer (HTL) to suppress the reaction between HTL and EML. The 15C5 molecule interacts with Cu+, Zn2+ and Sn2+ cations forming host-guest complexes to impede their migration, which is elucidated by density functional theory calculations. Additionally, 15C5 can neutralize lead (Pb) defects by the abundant oxygen (O) and high electronegative cavities to reduce the nonradiative recombination of FAPbBr3 film. This bidirectional anchoring strategy effectively improves hole charge transport efficiency and suppresses nonradiative recombination at the HTL/EML interface. As a result, the optimized PeLEDs present a 3.5 times peak external quantum efficiency (EQE) from 3.12% to 11.08% and the maximum luminance (Lmax) increased from 24495 to 50584 cd m-2. These findings offer innovative insights into addressing the metal ion migration issue commonly observed in inorganic HTLs.

Ions-induced Assembly of Perovskite Nanocomposites for Highly Efficient Light-Emitting Diodes with EQE Exceeding 30

Metal halide perovskites, a cost-effective class of semiconductos, hold great promise for display technologies that demand high-efficiency, color-pure light-emitting diodes (LEDs). Early research on three-dimensional (3D) perovskites showed low radiative efficiencies due to modest exciton binding energies. To inprove luminescence, reducing dimensionality or grain size has been a common approach. However, dividing the perovskite lattice into smaller units may hinder carrier transport, compromising electrical performance. Moreover, the increased surface area introduce additional surface trap states, leading to greater non-radiative recombination. Here, an ions-induced growth method is employed to assembe lattice-anchored perovskite nanocomposites for efficient LEDs with high color purity. This approach enables the nanocomposite thin films, composed of 3D CsPbBr3 and its variant of zero-dimensional (0D) Cs4PbBr6, to feature significant low trap-assisted nonradiative recombination, enhanced light out-coupling with a corrugated surface, and well-balanced charge carrier transport. Based on the resultant 3D/0D perovskite nanocomposites, the perovskite LEDs (PeLEDs) achieving an remarkable external quantum efficiency of 31.0% at the emission peak of 521 nm with a narrow full width at half-maximum of only 18 nm. This sets a new benchmark for color purity in high performance PeLED research, highlighting the significant advantage of this approach.

Modulation of Charge Transport Layer for Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (Pero-LEDs) have garnered significant attention due to their exceptional emission characteristics, including narrow full width at half maximum, high color purity, and tunable emission colors. Recent efficiency and operational stability advancements have positioned Pero-LEDs as a promising next-generation display technology. Extensive research and review articles on the compositional engineering and defect passivation of perovskite layers have substantially contributed to the development of multi-color and high-efficiency Pero-LEDs. However, the crucial aspect of charge transport layer (CTL) modulation in Pero-LEDs remains relatively underexplored. CTL modulation not only impacts the charge carrier transport efficiency and injection balance but also plays a critical role in passivating the perovskite surface, blocking ion migration, enhancing perovskite crystallinity, and improving light extraction efficiency. Therefore, optimizing CTLs is pivotal for further enhancing Pero-LED performance. Herein, this review discusses the roles of CTLs in Pero-LEDs and categorizes both reported and potential CTL materials. Then, various CTL optimization strategies are presented, alongside an analysis of the selection criteria for CTLs in high-performance Pero-LEDs. Finally, a summary and outlook on the potential of CTL modulation to further advance Pero-LED performances are provided.

Advances and Challenges in Large-Area Perovskite Light-Emitting Diodes

Metal halide perovskite light-emitting diodes (PeLEDs) have shown promise for high-definition displays and flat-panel lighting because of their wide color gamut, narrow emission band, and high brightness. The external quantum efficiency of PeLEDs increased rapidly from ≈1% to more than 25% in the past few years. However, most of these high-performance devices are fabricated using a spin coating method with a small device area of <0.1 cm2, limiting their commercial applications. Recently, large-area PeLEDs have attracted growing attention and significant breakthroughs have been reported. This perspective first introduces the pros and cons of each technique in making large-area PeLEDs. The advances in the fabrication of large-area PeLEDs are then summarized using spin coating and mass-production methods such as inkjet printing, blade coating, and thermal evaporation. Moreover, the challenging issues will be discussed that are urgent to be solved for large-area PeLEDs.

Unveiling the Carrier Dynamics of Perovskite Light-Emitting Diodes via Transient Electroluminescence

Perovskite light-emitting diodes (PeLEDs) have garnered significant attention due to their outstanding optoelectronic properties. However, investigating carrier transport and recombination behavior during device operation poses persistent challenges. In this study, we explore the impact of additive and interface engineering on device performance using transient electroluminescence (TREL). Polyethylene glycol (PEG) induces the formation of square-faceted nanocrystals with a homogeneous size distribution and extended fluorescence lifetime. Consequently, these PeLEDs exhibit remarkable stability. Additionally, employing an electron transport layer of 2,4,6-tris[3-(diphenylphosphino)phenyl]-1,3,5-triazine (PO-T2T), which has a better match to the energy bands of the perovskite layer and a higher carrier mobility, allows for lower turn-on voltage and faster response but also suffers from a short decay time and poor stability. Moreover, low-temperature TREL characterization shows that the carrier mobility is also significantly suppressed with decreasing temperature, which reduces the transient response speed.

Biodegradable and Ultra-High Expansion Ratio PPC-P Foams Achieved by Microcellular Foaming Using CO2 as Blowing Agent

Poly(propylene carbonate-co-phthalate) (PPC-P) is an amorphous copolymer of aliphatic polycarbonate and aromatic polyester; it possesses good biodegradability, superior mechanical performances, high thermal properties, and excellent affinity with CO2. Hence, we fabricate PPC-P foams in an autoclave by using subcritical CO2 as a physical blowing agent. Both saturation pressure and foaming temperature affect the foaming behaviors of PPC-P, including CO2 adsorption and desorption performance, foaming ratio, cell size, porosity, cell density, and nucleation density, which are investigated in this research. Moreover, the low-cost PPC-P/nano-CaCO3 and PPC-P/starch composites are prepared and foamed using the same procedure. The obtained PPC-P-based foams show ultra-high expansion ratio and refined microcellular structures simultaneously. Besides, nano-CaCO3 can effectively improve PPC-P's rheological properties and foamability. In addition, the introduction of starch into PPC-P can lead to a large number of open cells. Beyond all doubt, this work can certainly provide both a kind of new biodegradable PPC-P-based foam materials and an economic methodology to make biodegradable plastic foams. These foams are potentially applicable in the packaging, transportation, and food industry.

Enhancing Emission and Stability in Na-Doped Cs3Cu2I5 Nanocrystals

Lead-free Cs3Cu2I5 metal halides have garnered significant attention recently due to their non-toxic properties and deep-blue emission. However, their relatively low photoluminescence quantum efficiency and poor stability have limited their applications. In this work, sodium iodide (NaI) is used to facilitate the synthesis of Cs3Cu2I5 nanocrystals (NCs), demonstrating improved photoluminescence intensity, photoluminescence quantum yield, and stability. Systematic optoelectronic characterizations confirm that Na+ is successfully incorporated into the Cs3Cu2I5 lattice without altering its crystal structure. The improved Photoluminescence Quantum Yield (PLQY) and stability are attributed to the strengthened chemical bonding, which effectively suppresses vacancy defects in the lattice. Additionally, light-emitting diodes (LEDs) based on 10% NaI-doped Cs3Cu2I5 NCs were assembled, emitting vibrant blue light with a maximum radiant intensity of 82 lux and Commission Internationale de l'Eclairage (CIE) chromaticity coordinates of (0.15, 0.1). This work opens new possibilities for commercial lighting display applications.