Perovskite Light-Emitting Diodes with an External Quantum Efficiency Exceeding 30

Stable Blue CsPbBr3 Perovskite Nanocrystals with Near-Unity Photoluminescence Quantum Yield by Surface Ligand Engineering

All-inorganic cesium lead halide perovskites are emerging as a new promising candidate material in light-emitting diodes, photovoltaics, and photodetectors owing to their outstanding optical and electrical properties. However, blue perovskites still lag far behind the green and red analogues in terms of efficiency and stability. To avoid phase separation with mixed halide perovskite nanocrystals (e.g., CsPbBrxCl3-x), blue-emitting perovskites with a quantum confinement effect are very attractive. In this work, we designed a postsynthetic modification strategy with didodecyldimethylammonium bromide (DDAB) and lead bromide (PbBr2) to achieve blue-emitting CsPbBr3 nanocrystals (NCs) with nearly perfect surface passivation and excellent stability. The synergistic effect of DDAB and PbBr2 inhibited the possible perovskite phase transformation caused by DDA+, repaired the damaged [PbBr6]4- octahedra after purification, and created a halide-rich environment on the surface of NCs, thus maximizing the passivation of surface vacancy defects. In addition, the relatively short-chain, proton-free DDAB partially replaced the original organic ligands on the surface of NCs, resulting in near-unity photoluminescence quantum yield (PLQY) and remarkable stability. After 14 days of continuous ultraviolet irradiation at 365 nm, the PLQY of NCs was close to 100% and the photoluminescence (PL) spectrum remained almost unchanged. The PLQY of NCs remained greater than 90% after either continuous heating in an oil bath at 80 °C for 14 days or storage in the air for 2 months. This study demonstrates an effective approach to obtaining highly bright and stable blue perovskite NCs, which is expected to be used in optoelectronic devices, and provides strategies for future surface ligand engineering of perovskites.

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.

A Close-Space Fast Nucleation Strategy toward High-Efficiency Perovskite Light-Emitting Diodes

Halide perovskite light-emitting diodes (PeLEDs), considered as potential candidates for future displays, face significant limitations in their external quantum efficiency (EQE) due to an uncontrollable nucleation and crystallization process. Herein, a close-space inverted annealing (CSIA) strategy is developed to achieve fast nucleation and obtain a more uniform perovskite film with larger crystal domains and much lower defect centers. The increased surficial temperature and quick solvent evaporation in the CSIA method result in the fast formation of numerous large nuclei and solvate intermediates at the initial stage, which effectively guide crystal growth into large domains, facilitated by the residual solvent. The CSIA-processed PeLED achieves a peak EQE of 25.8%, which is among the best values of near-infrared devices. Moreover, it is applicable to perovskite-emitting layers with different defect passivation agents. This straightforward approach highlights a great opportunity to boost the performance and commercialization of perovskite optoelectronic devices.

Hole Delayed-Release Effect of Inorganic Interfacial Dipole Layer on Charge Balance for Boosting CsCu2I3 Light-Emitting Diodes

CsCu2I3 light-emitting diodes (LEDs) have attracted tremendous interest due to their environmental friendliness, low-cost processing, and broadband luminescence properties. However, their hole injection efficiency usually towers over electron injection efficiency owing to the intrinsic Cu vacancy-mediated excess hole concentration and wide bandgap of CsCu2I3, generating severe charge imbalance. Here, we designed an inorganic interfacial dipole layer (IDL) based on lithium chloride to exert a hole delayed-release effect for charge balance in CsCu2I3 LEDs by selectively modulating the energy levels of the contact layers. Accordingly, the IDL-based CsCu2I3 LEDs exhibit a record champion brightness of 2620 cd/m2 along with a three times enhanced peak external quantum efficiency of 3.73% at 565 nm. Meanwhile, the universality of the hole delayed-release effect of inorganic IDLs is verified by demonstrating enhanced CsCu2I3 LEDs incorporated with other alkali metal salt-based IDLs. This work provides a comprehensive guideline for optimizing the charge transport of lead-free LEDs by charge delayed-release effect of IDLs toward next-generation eco-friendly display applications.

Spacer Cation Engineering Enables Blue Quasi-2D Perovskites to Achieve Highly Efficient and Spectrally Stable Electroluminescence

The combination of organic spacer cations and mixed-halides to produce multiphase quasi-2D perovskites is a promising strategy for fabricating blue perovskite light-emitting diodes (PeLEDs). However, insufficient energy transfer, trap-assisted recombination and exciton-phonon coupling lead to significant non-radiative losses. Here, a co-spacer engineering strategy of binding guanidinium (GA+) and ortho-fluorophenylethylamium (oF-PEA+) through hydrogen bonds is proposed to prepare blue mixed-halide quasi-2D perovskite films with high photoluminescence quantum yields (PLQYs). GA+ with Lewis base characteristics reduces the trap states by defect passivation. Additionally, oF-PEA+ inhibits the rapid diffusion of GA+ by hydrogen bonding interactions, which mitigates the formation of undesirable low-dimensional phases and facilitates the growth of high-dimensional emissive phases with a more concentrated distribution, resulting in efficient energy transfer of excitons and weaker exciton-phonon coupling. These synergistic effects enable the blue perovskite films to achieve a PLQY as high as 91.5%. As a result, the fabricated blue PeLEDs show a remarkable external quantum efficiency of 21.1% at the stable emissionpeak of 489 nm with a narrow full width at half-maximum of 19 nm.

Blue Perovskite Light-Emitting Diodes Using Multifunctional Small Molecule Dopants

Unbalanced charge carrier injections and high densities of non-radiative recombination channels are still major obstacles to advancing high-efficiency blue perovskite light-emitting diodes (LEDs). Here, a deep-HOMO level p-type small molecule, (2-(3,6-dibromo-9H-carbazol-9-yl)ethyl)phosphonic acid, doped in blue perovskites for building a better-balanced injection and controlling over defects is demonstrated. During the perovskite film deposition process, most small molecules are extruded from the precursor solution to the bottom and top surfaces of the perovskite films. This unique distribution of molecules can construct a better-balanced carrier injection due to improved hole and retarded electron injection by its suitable energy-level structure, along with modulation of all defects in bulk and at the surface of doped films due to the formation of covalent bonds by its functional moiety. With this approach, a series of blue perovskite LEDs is designed with external quantum efficiencies (EQEs) of up to 24.03% (at a luminance of 113 cd m-2 and emission peak of 485 nm), 16.61% (at a luminance of 51 cd m-2 and emission peak of 476 nm) and 8.55% (at a luminance of 30 cd m-2 and emission perk of 467 nm), and encouraging operational stability.

Multi-cation synergy improves crystallization and antioxidation of CsSnBr3for lead-free perovskite light-emitting diodes

Tin (Sn) perovskites have emerged as promising alternatives to address the toxicity concerns associated with lead-based (Pb) perovskite light-emitting diodes (PeLEDs). However, the inherent oxidation of Sn perovskite films leads to a serious efficiency roll-off in PeLEDs at increased current densities. Although three-dimensional CsSnBr3perovskites exhibit decent carrier mobilities and thermal stability, their rapid crystallization during solution processing results in inadequate surface coverage. This inadequate coverage increases non-radiative recombination and leakage current, thereby hindering Sn PeLED performance. Herein, we present a multi-cation synergistic strategy by introducing the organic cations formamidinium (FA+) and thiophene ethylamine (TEA+) into CsSnBr3perovskites. The addition of organic cations delays crystallization by forming hydrogen bonds interacting with the CsSnBr3. The smaller FA+enters the perovskite lattice and improves crystallinity, while the larger TEA+cation enhances surface coverage and passivates defect states. By further optimizing the interface between PEDOT:PSS and perovskite layers through the use of ethanolamine and a thin layer of LiF, we achieved a red Sn-based PeLED with an emission wavelength of 670 nm, a maximum luminance of 151 cd m-2, and an external quantum efficiency of 0.21%.

Improved Crystallinity and Defect Passivation for Formamidinium Tin Iodide-Based Perovskite Light-Emitting Diodes

The toxicity of lead (Pb) presents a critical challenge for the application of perovskite optoelectronics. In tin (Sn) perovskite, Sn2+ is easily oxidized to Sn4+ during the crystallization process. The uncontrollable oxidation process affects the crystallinity of perovskite films and leads to nonradiative traps within the films, resulting in poor device performance. Herein, we improve the efficiency of formamidinium tin iodide (FASnI3)-based perovskite LEDs (PeLEDs) through the inclusion of phenyl-thioure (PTC), which enhances crystallinity and suppresses oxidation of the Sn perovskite emitters. We achieve a high-performance near-infrared FASnI3-based PeLED with a peak external quantum efficiency (EQE) of 6.4% and a maximum radiance of 117 W sr-1 m-2. The devices exhibit operational lifetimes (T50) of ∼12.4 h under a constant current density of 10 mA cm-2, representing some of the most stable FASnI3-based PeLEDs. Our work explores a pathway for regulating crystallinity, inhibiting oxidation, and passivating defects in lead-free Sn-based PeLEDs.

Efficient All-Solution-Processed Perovskite Light-Emitting Diodes via a Room-Temperature Vapor-Treated Interlayer

Metal halide perovskites hold great promise for cost-effective, solution-processed, light-emitting diodes (LEDs) due to their exceptional optoelectronic properties. However, fabricating all-solution-processed perovskite LEDs (PeLEDs) remains challenging because the perovskite emitters are susceptible to damage from subsequent solution layers. Here, we introduce a novel fabrication method that employs a low-pressure-treated electron-transport layer (ETL) at room temperature, complemented by a polyethylenimine (PEI) interface modification layer. Notably, the optimized PEI-modified CsPbBr3 exposed to air exhibits a remarkable 3-fold increase in photoluminescence intensity and maintains nearly constant light output for over 100 h, compared to pristine perovskite. Crucially, the incorporation of PEI significantly reduces the electron-transport barrier, mitigates the degradation of perovskite crystals caused by water and oxygen, and minimizes adverse interactions with solvents from the subsequent ETL. As a result, all-solution-processed PeLEDs incorporating an ETL subjected to a 20 min low-pressure treatment at 1 × 10-1 mbar at room temperature achieved an unprecedented external quantum efficiency of up to 4.6%, a record low turn-on voltage of 2.1 V for CsPbBr3, and an operational lifetime approximately 5 times longer than that of conventional devices. This strategy, both conceptually straightforward and easy to implement, offers a new avenue for the development of future printable PeLEDs.

Enhanced Electroluminescence and Stability of Sky-Blue Perovskite Light-Emitting Diodes

Although remarkable breakthroughs have been witnessed in the field of perovskite light-emitting diodes (PeLEDs), achieving efficient and stable blue PeLEDs still remains as a critical challenge to towards commercial applications. Inspired by the protection effect and water-repellent properties of swan feathers, 2H,2H,3H,3H-heptadecafluoroundecanoic acid (HFUA) has been designed as adsorbed functional molecule for blue perovskites, which can simultaneously enhance the electroluminescence performance and moisture stability. The HFUA molecule features a long-chain structure where the carboxylic acid group acts as an anchor, coordinating with undercoordinated lead atoms in blue perovskites. The fluorine atoms at the opposite end of the chain form ionic bonds with the halogen octahedron, thereby stabilizing the octahedral structure. In addition, HFUA adsorption lowers the adsorption energy of organic spacers on the perovskite lattice, optimizing the reduced-dimensional phase distribution to facilitate smooth exciton transfer. Furthermore, the unique molecular structure of HFUA, rich in fluorine atoms, enhances the hydrophobicity of the perovskite surface, effectively inhibiting moisture penetration and preventing perovskite hydrolysis. The target blue PeLEDs obtain a maximum external quantum efficiency of 22.88 % at 490 nm and exhibit greatly improved air stability under humid and high-temperature conditions. Our findings provide a unique and effective strategy for producing efficient and stable blue PeLEDs.

Construction and Multifunctional Photonic Applications of Light Absorption-Enhanced Silicon-Based Schottky Coupled Structures

To expand the detection capabilities of silicon (Si)-based photodetector and address key scientific challenges such as low light absorption efficiency and short carrier lifetime in Si-based graphene photodetector. This work introduces a novel Si-based Schottky coupled structure by in situ growth of 3D-graphene and molybdenum disulfide quantum dots (MoS2 QDs) on Si substrates using chemical vapor deposition (CVD) and plasma-enhanced chemical vapor deposition (PECVD) techniques. The findings validate the "dual-enhanced absorption" effect, enhancing the understanding of the mechanisms that improve optoelectronic performance. The synergistic effect of 3D-graphene's natural nano-resonant cavity and MoS2 QDs enhances light absorption efficiency and extends carrier lifetime. Introducing MoS2 QDs broadens and intensifies the built-in electric field, promoting the separation of photogenerated electrons and holes. The photodetector exhibits a wideband light response in the wavelength range of 380-2200 nm. It stably outputs photocurrent under high-frequency (1 kHz) modulated laser (2200 nm), with a responsivity (R) of 40 mA W-1 and detectivity (D*) of 1.15 × 109 Jones. Photodetectors show the ability to process and encrypt complex binary signals and achieve versatility in "AND" gate and "OR" gate logic operations, as well as image sensing (240 × 200 pixels).

Efficient Spin-Light-Emitting Diodes With Tunable Red to Near-Infrared Emission at Room Temperature

Spin light-emitting diodes (spin-LEDs) are important for spin-based electronic circuits as they convert the carrier spin information to optical polarization. Recently, chiral-induced spin selectivity (CISS) has emerged as a new paradigm to enable spin-LED as it does not require any magnetic components and operates at room temperature. However, CISS-enabled spin-LED with tunable wavelengths ranging from red to near-infrared (NIR) has yet to be demonstrated. Here, chiral quasi-2D perovskites are developed to fabricate efficient spin-LEDs with tunable wavelengths from red to NIR region by tuning the halide composition. The optimized chiral perovskite films exhibit efficient circularly polarized luminescence from 675 to 788 nm, with a photoluminescence quantum yield (PLQY) exceeding 86% and a dissymmetry factor (glum) ranging from 8.5 × 10-3 to 2.6 × 10-2. More importantly, direct circularly polarized electroluminescence (CPEL) is achieved at room temperature in spin-LEDs. This work demonstrated efficient red and NIR spin-LEDs with the highest external quantum efficiency (EQE) reaching 12.4% and the electroluminescence (EL) dissymmetry factors (gEL) ranging from 3.7 × 10-3 to 1.48 × 10-2 at room temperature. The composition-dependent CPEL performance is further attributed to the prolonged spin lifetime as revealed by ultrafast transient absorption spectroscopy.

Multiple Chemical Interactions in Additive Engineering of Perovskite for Enhanced Efficiency and Stability of Pure Blue Light-Emitting Diodes

Additive engineering is extensively employed in perovskite light-emitting diodes (PeLEDs) to enhance the device performance. However, the effectiveness of additives is restricted, as they generally interact with only one or two components within the perovskite structure. Consequently, these additives are unable to fulfill the comprehensive functional requirements imposed by perovskite light-emitting materials. In this work, we successfully designed and synthesized a multifunctional additive of N-(perfluorophenyl)-P,P-diphenylphosphinic amide (PFNPO) via a one-step synthesis approach. Multiple chemical interactions can be provided between PFNPO and different perovskite components, thereby effectively modulating quasi-two-dimensional (quasi-2D) perovskite crystallization, passivating coordination-unsaturated Pb defects, and suppressing halide ion migration simultaneously. Based on these synergistic effects, the incorporation of PFNPO in pure blue quasi-2D PeLEDs resulted in a significant enhancement in external quantum efficiency from 1.83 to 4.26%, an operational lifetime that was extended by more than 3-fold, and improved spectral stability at 466 nm.

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.

Probing ionic conductivity and electric field screening in perovskite solar cells: a novel exploration through ion drift currents

It is widely accepted that mobile ions are responsible for the slow electronic responses observed in metal halide perovskite-based optoelectronic devices, and strongly influence long-term operational stability. Electrical characterisation methods mostly observe complex indirect effects of ions on bulk/interface recombination, struggle to quantify the ion density and mobility, and are typically not able to fully quantify the influence of the ions upon the bulk and interfacial electric fields. We analyse the bias-assisted charge extraction (BACE) method for the case of a screened bulk electric field, and introduce a new characterisation method based on BACE, termed ion drift BACE. We reveal that the initial current density and current decay dynamics depend on the ion conductivity, which is the product of ion density and mobility. This means that for an unknown high ion density, typical in perovskite solar absorber layers, the mobility cannot be directly obtained from BACE measurements. We derive an analytical model to illustrate the relation between current density, conductivity and bulk field screening, supported by drift-diffusion simulations. By measuring the ion density independently with impedance spectroscopy, we show how the ion mobility can be derived from the BACE ion conductivity. We highlight important differences between the low- and high-ion density cases, which reveal whether the bulk electric field is fully screened or not. Our work clarifies the complex ion-related processes occurring within perovskite solar cells and gives new insight into the operational principles of halide perovskite devices as mixed ionic-electronic conductors.

Low-Dimensional Lead-Free Metal Halides for Efficient Electrically Driven Light-Emitting Diodes

Electrically driven light-emitting diodes (ED LEDs) based on 3D metal halide perovskites have seen remarkable advancements during the past decade. However, the highest-performing devices are largely based on lead-containing 3D perovskites, presenting two key challenges - toxicity and stability - that must be addressed for commercialization. Reducing structural dimensionality and incorporating non-lead metals present promising pathways to address these issues. Although research on ED LEDs based on low-dimensional, lead-free metal halides (LD LFMHs) is growing, their performance still significantly lags behind that of 3D lead halide perovskites. This review seeks to deliver a comprehensive overview of ED LEDs based on LD LFMHs, covering a brief history of their development, methods for material synthesis, luminescence mechanisms, and applications in electroluminescent devices. It also examines current challenges and proposes practical strategies to enhance device performance, with the goal of inspiring further progress in the field.

Inhibiting ion migration in strontium-lead halide perovskite for pure-blue emission: a first-principle and experimental study

Bromide-chloride mixed perovskites have garnered significant attention as a direct and efficient material for achieving pure-blue emission. However, the complex problem of halide migration in mixed halide perovskites presents a significant obstacle to achieving stable electroluminescence (EL) spectra. Here, we investigate the mechanism of partially replacing the B-site Pb2+ with the non-toxic Sr2+ to achieve pure-blue emission based on first principles. The ion mobility activation energy of Sr2+ is 1.23 eV, which is an order of magnitude greater than that of halogens. Meanwhile, the incorporation of Sr2+ triples the activation energy for halogen migration. Furthermore, the halide defect formation energy increases from 4.75 eV to 5.62 eV, thereby reducing ion migration channels. Transient absorption spectroscopy demonstrates that suppressing the ion mobility pathway and enhancing ion mobility activation energy promotes the perovskite film to exhibit excellent spectral stability under laser pumping. Our work provides insights for the development of highly stable and eco-friendly perovskite devices.

Improving the light extraction efficiency of white-light perovskite light-emitting diodes based on quantum dot nanowires

This study introduces an innovative strategy to enhance the light extraction efficiency (LEE) of white-light perovskite light-emitting diodes (PeLEDs) by incorporating quantum dot nanowires (QD-NWs) that are prepared by a porous anodic aluminum (PAA) substrate. The QD-NWs were synthesized through a combination of inkjet printing and vacuum deposition based on the PAA substrate which features a unique waveguiding structure that redirects post-color conversion fluorescence along its axis, effectively minimizing energy losses such as reabsorption loss and total internal reflection (TIR) loss. Empirical evidence indicates a significant luminance enhancement of 43.79%, accompanied by an enhancement in current efficiency, for PeLEDs incorporating the QD-NWs. By fine-tuning the structural attributes of the PAA substrate to regulate the size of QD-NWs, this research has successfully developed white-light PeLEDs based on quasi-2D blue perovskite, offering a universal strategy for boosting LEE and propelling the evolution of white-light PeLED technology.

Regulation of nucleation and crystallization for blade-coating large-area CsPbBr3 perovskite light-emitting diodes

Metal halide perovskite light-emitting diodes (PeLEDs) and large-area perovskite color conversion layers for liquid crystal display exhibit great potential in the field of illumination and display. Blade-coating method stands out as a highly suitable technique for fabricating large-scale films, albeit with challenges such as uneven nucleation coverage and non-uniformity crystallization process. In this work, we developed an in-situ characterization measurement system to monitor the perovskite nucleation, and crystallization process. By incorporating formamidine acetate (FAAc) into perovskite precursor solutions, the nucleation rate and nuclei density of perovskite were increased, leading to more uniform nucleation. In addition, we inserted a layer of [2-(9H-carbazol-9-yl)ethyl] phosphonic acid above the poly(9-vinylcarbazole) hole transport layer. This layer acts as an anchor for the perovskite nano-crystal nuclei formed in the precursor, enhancing the steric hindrance of the solute and subsequently slowing down the crystal growth rate, thereby improving crystal quality. Based on these improvements, large-area perovskite nano-polycrystalline films with significantly improved uniformity and enhanced photoluminescence quantum yield were obtained. A small-area PeLED (2 mm × 2 mm) with a maximum external quantum efficiency of 25.91% was realized, marking the highest record of PeLED prepared by blade-coating method to date. An ultra-large-area PeLED (5 cm × 7 cm) was also prepared, which is the largest PeLED prepared by the solution method reported so far.

Highly bright perovskite light-emitting diodes enabled by retarded Auger recombination

One of the key advantages of perovskite light-emitting diodes (PeLEDs) is their potential to achieve high performance at much higher current densities compared to conventional solution-processed emitters. However, state-of-the-art PeLEDs have not yet reached this potential, often suffering from severe current-efficiency roll-off under intensive electrical excitations. Here, we demonstrate bright PeLEDs, with a peak radiance of 2409 W sr-1 m-2 and negligible current-efficiency roll-off, maintaining high external quantum efficiency over 20% even at current densities as high as 2270 mA cm-2. This significant improvement is achieved through the incorporation of electron-withdrawing trifluoroacetate anions into three-dimensional perovskite emitters, resulting in retarded Auger recombination due to a decoupled electron-hole wavefunction. Trifluoroacetate anions can additionally alter the crystallization dynamics and inhibit halide migration, facilitating charge injection balance and improving the tolerance of perovskites under high voltages. Our findings shed light on a promising future for perovskite emitters in high-power light-emitting applications, including laser diodes.

Bottom Electrode Modification Enables Efficient and Bright Silicon-Based Top-Emission Perovskite Light-Emitting Diodes

The integration of perovskites with mature silicon platform has emerged as a promising approach in the development of efficient on-chip light sources and high-brightness displays. However, the performance of Si-based green perovskite light-emitting diodes (PeLEDs) still falls significantly short compared to their red and near-infrared counterparts. In this study, it is revealed that the high work function Au, widely employed in Si-based top-emission PeLEDs as the reflective bottom electrode, exhibits considerably lower reflectivity in the green spectrum than in the longer wavelengths. Consequently, Ag electrode is introduced to replace Au to enhance the green light reflectivity, and the ultrathin MoO3 and self-assembled monolayers (SAMs) are sequentially deposited for surface modification. These results indicate that the MoO3 layer removes the energy barrier at Ag/polymer hole transport layer interface, enhancing the hole injection efficiency; while the SAMs firmly anchor onto the MoO3 layer, effectively preventing interfacial defect formation. Benefited from this organic/inorganic dual-layer modification strategy, Si-based green PeLEDs with an impressive peak external quantum efficiency of 18.2% and a maximum brightness of 81931 cd m-2 are successfully fabricated, on par with those of the red and near-infrared counterparts. This achievement marks an advancement in developing high-performance Si-based PeLEDs with full-spectrum output.

Enhanced Hole-Injecting Interface for High-Performance Deep-Blue Perovskite Light-Emitting Diodes Using Dipole-Controlled Self-Assembled Monolayers

The Blue electroluminescence (EL) with high brightness and spectral stability is imperative for full-color perovskite display technologies meeting the Rec. 2020 standard. However, deep-blue perovskite light-emitting diodes (PeLEDs) lag behind their green- or red-emitting counterparts in brightness, quantum efficiency, and operational stability. Additionally, the Cl-/Br- mixed-halide perovskites with wide bandgap typically designed for deep-blue emitters are prone to degradation quickly under high operating bias due to low energy for halide migrations and vacancies formation, posing a significant challenge to spectral/operative stabilities. To address these issues, high-performance deep-blue PeLEDs are demonstrated by tuning the interface properties with Br-2ETP, a self-assembled monolayer (SAM) molecule engineered for a high dipole moment. The Br-2EPT-based hole-injecting interface facilitates favorable energy level alignment between indium tin oxide and the deep-lying valence band of the perovskite layer, suppressing the hole-injecting barrier and non-radiative charge recombination. Excellent perovskite film morphologies are observed at the top and buried surfaces by Br-2EPT, improving the balance of carrier injection for light emission efficiency. Consequently, the devices exhibit deep-blue electroluminescence at 457 nm, with an external quantum efficiency of 6.56% and spectral/operative stabilities.

The Perovskite Optoelectronic Devices - A Look at the Future

The perovskite materials are broadly incorporated into optoelectronic devices due to a number of advantages. Their rapid technological progress is related to the relatively simple fabrication process, low production cost and high efficiency. Significant improvement is made in the light emitting, detection performance and device design especially operating in the visible and near-infrared regions. This review presents the status and possible future development of the perovskite devices such as solar cells, photodetectors, and light-emitting diodes. The fundamental properties of perovskite materials related to their effective device applications are summarized. Since the development of the perovskite technology is mainly driven by the revolutionary evolution of the semiconductor perovskite solar cell as a robust candidate for next-generation solar energy harvesting, this topic is considered first. The device engineering of various perovskite photodetector structures, including perovskite quantum dot photodetectors, is then discussed in detail. Their performance is compared with the current commercial photodetectors available on the global market together with their challenges. Finally, the considerable progress in the fabrication of the perovskite light-emitting diodes with external quantum efficiency exceeding 20% is presented. The paper is completed in an attempt to determine the development of perovskite optoelectronic devices in the future.

Ultrafast Carrier Diffusion in Perovskite Monocrystalline Films

Monocrystalline perovskite materials exhibit superior properties compared with polycrystalline perovskites, including lower defect density, minimal grain boundaries, and enhanced carrier mobility. Nevertheless, the preparation of large-area, high-quality single-crystal films, which could prove invaluable for photoelectronic applications, remains a significant challenge. The study of how their unique properties go beyond polycrystalline thin films is still missing. In our experiment, using polarization-selective transient absorption microscopy, we directly observed the spatial carrier transportation in methylammonium lead iodide (CH3NH3PbI3, MAPbI3) strip-shaped monocrystalline ultrathin films. Ultrafast carrier diffusion transportation was observed. The monocrystalline carrier diffusion coefficient D (∼22 cm2 s-1) is an order of magnitude higher than that in polycrystalline films. Anisotropic carrier diffusion of the MAPbI3 single crystal has been discovered. It is also discovered that the electrons and holes are of different anisotropy and diffusion speed. This ultralong carrier transport inside the monocrystalline film provides solid support for the development of perovskite based photoelectronic devices.

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.

Spin-Orbital Ordering Effects of Light Emission in Organic-Inorganic Hybrid Metal Halide Perovskites

Organic-inorganic hybrid metal halide perovskites carrying strong spin-orbital coupling (SOC) have demonstrated remarkable light-emitting properties in spontaneous emission, amplified spontaneous emission (ASE), and circularly-polarized luminescence (CPL). Experimental studies have shown that SOC plays an important role in controlling the light-emitting properties in such hybrid perovskites. Here, the SOC consists of both orbital (L) and spin (S) momentum, leading to the formation of J (= L + S) excitons intrinsically involving orbital and spin momentum. In general, there are three issues in determining the effects of SOC on the light-emitting properties of J excitons. First, when the J excitons function as individual quasi-particles, the configurations of orbital and spin momentum directly decide the formation of bright and dark J excitons. Second, when the J excitons are mutually interacting as collective quasi-particles, the exciton-exciton interactions can occur through orbital and spin momentum. The exciton-exciton interactions through orbital and spin momentum give rise to different light-emitting properties, presenting SOC ordering effects. Third, the J excitons can develop ASE through coherent exciton-exciton interaction and CPL through exciton-helical ordering effect. This review article discusses the SOC effects in spontaneous emission, ASE, and CPL in organic-inorganic hybrid metal halide perovskites.

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.

Enhanced light extraction by optimizing near-infrared perovskite-based light emitting diode (PeLED)

One of the outstanding optoelectronic devices is perovskite-based light emitting diodes (PeLEDs) that have diverse applications according to the wavelength of produced light. However, these devices have shown more than 20% External Quantum Efficiency (EQE), in comparison with their counterparts (OLEDs), light extraction is limited in these devices. In this paper, by optimizing the thickness of layers and manipulating absorption in the active layer (AL), the light extraction efficiency (LEE) increased by nearly 20%. It reached 42.89% in the near-infrared (NIR) region of the wavelength, by considering the CH(NH2)2PbI3 perovskite, in the emissive layer (EML).

Ultrabright and Efficient Green Perovskite Light-Emitting Diodes Enabled by Well-Crystallized Dense CsPbBr3 Nanocubes

Perovskite light-emitting diodes (PeLEDs) are promising for next-generation high-definition displays. One of the keys to achieving high performance PeLEDs lies in how to fabricate crystalline and dense perovskite films. However, there exist challenges to directly grow well-crystallized CsPbBr3 nanocrystal thin films on transport layers due to low solubility in solvents and fast precipitation of all-inorganic CsPbBr3, and the corresponding bright, efficient, and stable green PeLEDs have rarely been reported. Herein, we report an efficient strategy to prepare well-crystallized and dense CsPbBr3 nanocubes for ultrabright and efficient green PeLEDs. We introduce sulfobetaine zwitterion as crystallization control agent and strontium fluoride nanocrystals as nucleation seeds to grow high-quality CsPbBr3 nanocube films. Eventually, the CsPbBr3 films enable green PeLEDs with a maximum luminance of 162 767 cd m-2 and a champion external quantum efficiency of 21.3% along with a narrow spectral line width of ∼14.7 nm, representing state-of-the-art performances in green PeLEDs.

Revealing the Role of Organic Ligands in Deep-Blue-Emitting Colloidal Europium Bromide Perovskite Nanocrystals

Europium halide perovskites are promising candidates for environmentally benign blue-light emitters with their narrow emission line width. However, the development of high-photoluminescence quantum yield (PLQY) colloidal europium halide perovskite nanocrystals (PNCs) is hindered by limited synthetic methods and elusive reaction mechanisms. Here, we provide an effective synthetic route for achieving high-PLQY deep-blue-emitting colloidal CsEuBr3 PNCs. Using two Br-organic ligand precursors, oleylammonium bromide (OLAMHBr) and trioctylphosphine dibromide (TOPBr2), we identified distinct phase evolution routes involving Eu2+:CsBr, Cs4EuBr6, and CsEuBr3. The OLAMHBr precursor initially promotes the formation of the Eu2+:CsBr phase, which reorganizes into the CsEuBr3 perovskite phase via proton transfer. In contrast, the TOPBr2 precursor induces the formation of core/shell Cs4EuBr6/CsBr PNCs, which subsequently transform into CsEuBr3 through nucleophilic addition. The TOPBr2 route exhibited enhanced CsEuBr3 phase homogeneity, resulting in a significantly higher PLQY (40.5%; full width at half-maximum (fwhm) = 24 at 430 nm), compared to the OLAMHBr route (16.5% at 418 nm). Notably, the phase-pure CsEuBr3 PNCs demonstrated a world-record PLQY among the reported blue-emitting lead-free PNCs that exhibit a narrow emission line width (fwhm <25 nm). This work highlights the significant role of organic ligands in the colloidal synthesis of CsEuBr3 PNCs and their potential as nontoxic, solution-processable blue-light emitters.

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.

Monoammonium Modified Dion-Jacobson Quasi-2D Perovskite for High Efficiency Pure-Blue Light Emitting Diodes

Quasi-2D perovskites exhibit impressive optoelectronic properties and hold significant promise for future light-emitting devices. However, the efficiency of perovskite light-emitting diodes (PeLEDs) is seriously limited by defect-induced nonradiative recombination and imbalanced charge injection. Here, the defect states are passivated and charge injection balance is effectively improved by introducing the additive cyclohexanemethylammonium (CHMA) to bromide-based Dion-Jacobson (D-J) structure quasi-2D perovskite emission layer. CHMA participates in the crystallization of perovskite, leading to high quality film composed of compact and well-contacted grains with enhanced hole transportation and less defects. As a result, the corresponding PeLEDs exhibit stable pure blue emission at 466 nm with a maximum external quantum efficiency (EQE) of 9.22%. According to current knowledge, this represents the highest EQE reported for pure-blue PeLEDs based on quasi-2D bromide perovskite thin films. These findings underscore the potential of quasi-2D perovskites for advanced light-emitting devices and pave the way for further advancements in PeLEDs.

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.

Phase stabilization via A-site ion anchoring for ultra-stable perovskite light emitting diodes

A novel ion anchoring strategy stabilizes the perovskite phase, yielding ambient stable perovskite films and ultra-stable perovskite light-emitting diodes (PeLEDs) with an unprecedented operational half-lifetime over 37.2 years at 100 cd m-2 and exceeding 27% efficiency, marking a new stability benchmark for next-generation display and lighting applications.

Lead-Free Perovskite Light-Emitting Diodes

Metal halide perovskites have been identified as a promising class of materials for light-emitting applications. The development of lead-based perovskite light-emitting diodes (PeLEDs) has led to substantial improvements, with external quantum efficiencies (EQEs) now surpassing 30% and operational lifetimes comparable to those of organic LEDs (OLEDs). However, the concern over the potential toxicity of lead has motivated a search for alternative materials that are both eco-friendly and possess excellent optoelectronic properties, with lead-free perovskites emerging as a strong contender. In this review, the properties of various lead-free perovskite emitters are analyzed, with a particular emphasis on the more well-reported tin-based variants. Recent progress in enhancing device efficiencies through refined crystallization processes and the optimization of device configurations is also discussed. Additionally, the remaining challenges are examined, and propose strategies that may lead to stable device operation. Looking forward, the potential future developments for lead-free PeLEDs are considered, including the extension of spectral range, the adoption of more eco-friendly deposition techniques, and the exploration of alternative materials.

CsPb2Br5 Plates/Quasi-2D Perovskite Heterojunction for Efficient Sky-Blue Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have gained significant attention owing to their remarkable tunability and color stability, and substantial progress has been made with green and red PeLEDs. However, the advancement of blue PeLEDs still lags far behind their red and green counterparts. In this study, we report efficient sky-blue PeLEDs utilizing an in situ fabricated CsPb2Br5 plates/quasi-2D perovskite heterojunction using chelating molecules to modulate the crystallization process of perovskites. The wide bandgap of CsPb2Br5 facilitated the formation of a type-I band alignment at the heterojunction, allowing efficient carrier transfer from CsPb2Br5 to CsPbBr3. This heterojunction leads to a noteworthy enhancement of device efficiency. The PeLEDs exhibit a maximum brightness of 2311 cd m-2, accompanied by a maximum external quantum efficiency of 12.86% at 487 nm. Our tailored design of CsPb2Br5/perovskite heterojunction thin films offers a promising avenue for advancing PeLED performance. This work contributes valuable insights into the burgeoning field of perovskite electroluminescence, paving the way for further optimization of PeLED technologies.

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.

Organic-Inorganic Hybrid Cuprous-Based Metal Halides with Unique Two-Dimensional Crystal Structure for White Light-Emitting Diodes

Ternary cuprous (Cu+)-based metal halides, represented by cesium copper iodide (e.g., CsCu2I3 and Cs3Cu2I5), are garnering increasing interest for light-emitting applications owing to their intrinsically high photoluminescence quantum yield and direct band gap. Toward electrically driven light-emitting diodes (LEDs), it is highly desirable for the light emitters to have a high structural dimensionality as it may favor efficient electrical injection. However, unlike lead-based halide perovskites whose light-emitting units can be facilely arranged in three-dimensional (3D) ways, to date, nearly all ternary Cu+-based metal halides crystallize into 0D or 1D networks of Cu-X (X=Cl, Br, I) polyhedra, whereas 3D and even 2D structures remain mostly uncharted. Here, by employing a fluorinated organic cation, we report a new kind of ternary Cu+-based metal halides, (DFPD)CuX2 (DFPD+=4,4-difluoropiperidinium), which exhibits unique 2D layered crystal structure. Theoretical calculations reveal a highly dispersive conduction band of (DFPD)CuBr2, which is beneficial for charge carrier injection. It is also of particular significance to find that the 2D (DFPD)CuBr2 crystals show appealing properties, including improved ambient stability and an efficient warm white-light emission, making it a promising candidate for single-component lighting and display applications.

Matched Electron-Transport Materials Enabling Efficient and Stable Perovskite Quantum-Dot-Based Light-Emitting Diodes

Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs), abbreviated as P-QLEDs have been regarded as significantly crucial emitters for lighting and displays. Efficient and stable P-QLEDs still lack ideal electron transport materials (ETM), which could efficiently block hole, transport electron, reduce interface non-radiative recombination and possess high thermal stability. Here, we report 2,4,6-Tris(3'-(pyridine-3-yl) biphenyl-3-yl)-1,3,5-triazine (TmPPPyTz, 3P) with strong electron-withdrawing moieties of pyridine and triazine to modulate the performance of P-QLEDs. Compared with commonly used 1,3,5-Tris(1-phenyl-1H-benzimidazol-2-yl)benzene (TPBi), the pyridine in 3P have a strong interaction with perovskites, which can effectively suppress the interface non-radiative recombination caused by the Pb2+ defects on the surface of QDs. In addition, 3P have deep highest occupied molecular orbital (HOMO) (enhancing hole-blocking properties), matched lowest unoccupied molecular orbital (LUMO) and excellent electron mobility (enhancing electron transport properties), realizing the carrier balance and maximizing the exciton recombination. Furthermore, high thermal resistance of 3P obviously improves the stability of QDs under variable temperature, continuous UV illumination, and electric field excitation. Resultantly, the P-QLEDs using the 3P as ETM achieved an outstanding performance with a champion EQE of 30.2 % and an operational lifetime T50 of 3220 hours at an initial luminance of 100 cd m-2, which is 151 % and about 11-fold improvement compared to control devices (EQE=20 %, T50=297 hours), respectively. These results provide a new concept for constructing the efficient and stable P-QLEDs from the perspective of selective ETM.

Inhibiting the Appearance of Green Emission in Mixed Lead Halide Perovskite Nanocrystals for Pure Red Emission

Mixed halide perovskites exhibit promising optoelectronic properties for next-generation light-emitting diodes due to their tunable emission wavelength that covers the entire visible light spectrum. However, these materials suffer from severe phase segregation under continuous illumination, making long-term stability for pure red emission a significant challenge. In this study, we present a comprehensive analysis of the role of halide oxidation in unbalanced ion migration (I/Br) within CsPbI2Br nanocrystals and thin films. We also introduce a new approach using cyclic olefin copolymer (COC) to encapsulate CsPbI2Br perovskite nanocrystals (PNCs), effectively suppressing ion migration by increasing the corresponding activation energy. Compared with that of unencapsulated samples, we observe a substantial reduction in phase separation under intense illumination in PNCs with a COC coating. Our findings show that COC enhances phase stability by passivating uncoordinated surface defects (Pb2+ and I-), increasing the formation energy of halide vacancies, improving the charge carrier lifetime, and reducing the nonradiative recombination density.

The marriage of perovskite nanocrystals with lanthanide‐doped upconversion nanoparticles for advanced optoelectronic applications

The exceptional optoelectronic properties of lead halide perovskite nanocrystals (PeNCs) in the ultraviolet and visible spectral regions have positioned them as a promising class of semiconductor materials for diverse optoelectronic and photovoltaic applications. However, their limited response to near‐infrared (NIR) light due to the intrinsic bandgap (>1.5 eV) has hindered their applications in many advanced technologies. To circumvent this limitation, it is of fundamental significance to integrate PeNCs with lanthanide‐doped upconversion nanoparticles (UCNPs) that are capable of efficiently converting low‐energy NIR photons into high‐energy ultraviolet and visible photons. By leveraging the energy transfer from UCNPs to PeNCs, this synergistic combination can not only expand the NIR responsivity range of PeNCs but also introduce novel emission profiles to upconversion luminescence with multi‐dimensional tunability (e.g., wavelength, lifetime, and polarization) under low‐to‐medium power NIR irradiation, which breaks through the inherent restrictions of individual PeNCs and UCNPs and thereby opens up new opportunities for materials and device engineering. In this review, we focus on the latest advancements in the development of PeNCs‐UCNPs nanocomposites, with an emphasis on the controlled synthesis and optical properties design for advanced optoelectronic applications such as full‐spectrum solar cells, NIR photodetectors, and multilevel anticounterfeiting. Some future efforts and prospects toward this active research field are also envisioned.

Ultralow voltage-driven efficient and stable perovskite light-emitting diodes

The poor operational stability of perovskite light-emitting diodes (PeLEDs) remains a major obstacle to their commercial application. Achieving high brightness and quantum efficiency at low driving voltages, thus effectively reducing heat accumulation, is key to enhancing the operational lifetime of PeLEDs. Here, we present a breakthrough, attaining a record-low driving voltage while maintaining high brightness and efficiency. By thoroughly suppressing interface recombination and ensuring excellent charge transport, our PeLEDs, with an emission peak at 515 nanometers, achieve a maximum brightness of 90,295 candelas per square meter and a peak external quantum efficiency of 27.8% with an ultralow turn-on voltage of 1.7 volts (~70% bandgap voltage). Notably, Joule heat is nearly negligible at these low driving voltages, substantially extending the operational lifetime to 7691.1 hours. Our optimized strategies effectively tackle stability issue through thermal management, paving the way for highly stable PeLEDs.

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%.

Strongly-confined colloidal lead-halide perovskite quantum dots: from synthesis to applications

Colloidal semiconductor nanocrystals enable the realization and exploitation of quantum phenomena in a controlled manner, and can be scaled up for commercial uses. These materials have become important for a wide range of applications, from ultrahigh definition displays, to solar cells, quantum computing, bioimaging, optical communications, and many more. Over the last decade, lead-halide perovskite nanocrystals have rapidly gained prominence as efficient semiconductors. Although the majority of studies have focused on large nanocrystals in the weak- to intermediate-confinement regime, quantum dots (QDs) in the strongly-confined regime (with sizes smaller than the Bohr diameter, which ranges from 4-12 nm for lead-halide perovskites) offer unique opportunities, including polarized light emission and color-pure, stable luminescence in the region that is unattainable by perovskites with single-halide compositions. In this tutorial review, we bring together the latest insights into this emerging and rapidly growing area, focusing on the synthesis, steady-state optical properties (including exciton fine-structure splitting), and transient kinetics (including hot carrier cooling) of strongly-confined perovskite QDs. We also discuss recent advances in their applications, including single photon emission for quantum technologies, as well as light-emitting diodes. We finish with our perspectives on future challenges and opportunities for strongly-confined QDs, particularly around improving the control over monodispersity and stability, important fundamental questions on the photophysics, and paths forward to improve the performance of perovskite QDs in light-emitting diodes.

Recent Advances in Carbazole-Based Self-Assembled Monolayer for Solution-Processed Optoelectronic Devices

Self-assembled molecules (SAMs) have shown great potential in the application of optoelectronic devices due to their unique molecular properties. Recently, emerging phosphonic acid-based SAMs, 2-(9Hcarbazol-9-yl)ethyl]phosphonic acid (2PACz), have successfully applied in perovskite solar cells (PSCs), organic solar cells (OSCs) and perovskite light emitting diodes (PeLEDs). More importantly, impressive results based on 2PACz SAMs are reported recently in succession. Therefore, it is essential to provide an insightful summary to promote it further development. In this review, the molecule design strategies about 2PACz are first concluded. Subsequently, this work systematically reviews the recent advances of 2PACz and its derivatives for single junction PSCs, tandem PSCs, OSCs and PeLEDs. Finally, this work concludes and discusses future challenges for 2PACz and its derivatives to further develop in optoelectronic devices.

Buried interface modification and light outcoupling strategy for efficient blue perovskite light-emitting diodes

Perovskite light-emitting diodes (PeLEDs) exhibit remarkable potential in the field of displays and solid-state lighting. However, blue PeLEDs, a key element for practical applications, still lag behind their green and red counterparts, due to a combination of strong nonradiative recombination losses and unoptimized device structures. In this report, we propose a buried interface modification strategy to address these challenges by focusing on the bottom-hole transport layer (HTL) of the PeLEDs. On the one hand, a multifunctional molecule, aminoacetic acid hydrochloride (AACl), is introduced to modify the HTL/perovskite interface to regulate the perovskite crystallization. Experimental investigations and theoretical calculations demonstrate that AACl can effectively reduce the nonradiative recombination losses in bulk perovskites by suppressing the growth of low-n perovskite phases and also the losses at the bottom interface by passivating interfacial defects. On the other hand, a self-assembly nanomesh structure is ingeniously developed within the HTLs. This nanomesh structure is meticulously crafted through the blending of poly-(9,9-dioctyl-fluorene-co-N-(4-butyl phenyl) diphenylamine) and poly (n-vinyl carbazole), significantly enhancing the light outcoupling efficiency in PeLEDs. As a result, our blue PeLEDs achieve remarkable external quantum efficiencies, 20.4% at 487 nm and 12.5% at 470 nm, which are among the highest reported values. Our results offer valuable insights and effective methods for achieving high-performance blue PeLEDs.

Highly efficient blue light-emitting diodes based on mixed-halide perovskites with reduced chlorine defects

Perovskite light-emitting diodes (PeLEDs) provide excellent opportunities for low-cost, color-saturated, and large-area displays. However, the performance of blue PeLEDs lags far behind that of their green and red counterparts. Here, we show that the external quantum efficiencies (EQEs) of blue PeLEDs scale linearly with the photoluminescence quantum yields (PL QYs) of CsPb(BrxCl1-x)3 nanocrystals emitting at 460 to 480 nm. The recombination efficiency of carriers is highly sensitive to the chlorine content and the related deep-level defects in nanocrystals, causing notable EQE drops even with minor increases in chlorine defects. Minor adjustments of chlorine content through rubidium compensation on the A-site effectively suppress the formation of nonradiative defects, improving PL QYs while retaining desirable bandgaps for blue-emitting nanocrystals. Our PeLEDs with record-high efficiencies span the blue spectrum, achieving peak EQEs of 12.0% (460 nm), 16.7% (465 nm), 21.3% (470 nm), 24.3% (475 nm), and 26.4% (480 nm). This work exemplifies chlorine-defect control as a key design principle for high-efficiency blue PeLEDs.

Improved Molecular Packing of Self-Assembled Monolayer Charge Injectors for Perovskite Light-Emitting Diodes

Self-assembled monolayers (SAMs) have shown great potential as hole injection materials for perovskite light-emitting diodes due to their low parasitic absorption and ability to adjust energy level alignment. However, the head and anchoring groups on SAM molecules with significant differences in polarity can lead to the formation of micelles in the commonly used alcoholic processing solvent, inhibiting the formation of an intact SAM. In this work, the introduction of methyl groups on carbazole in the phosphonic-acid-based SAM materials is found to facilitate energy level alignment and promote the formation of compact SAMs. The alternative molecular structure also enhances the solvent resistance of poly(9-vinylcarbazole), suppressing interfacial defect densities and nonradiative recombination processes in the emissive perovskites. PeLEDs based on the methyl-containing SAMs exhibit ∼30% enhancement in efficiency. These findings contribute to a better understanding of the design of SAM materials for PeLED applications.

Efficient Large-Area (81 cm2) Ternary Copper Halides Light-Emitting Diodes with External Quantum Efficiency Exceeding 13% via Host-Guest Strategy

Ternary copper (Cu) halides are promising candidates for replacing toxic lead halides in the field of perovskite light-emitting diodes (LEDs) toward practical applications. However, the electroluminescent performance of Cu halide-based LEDs remains a great challenge due to the presence of serious nonradiative recombination and inefficient charge transport in Cu halide emitters. Here, the rational design of host-guest [dppb]2Cu2I2 (dppb denotes 1,2-bis[diphenylphosphino]benzene) emitters and its utility in fabricating efficient Cu halide-based green LEDs that show a high external quantum efficiency (EQE) of 13.39% are reported. The host-guest [dppb]2Cu2I2 emitters with mCP (1,3-bis(N-carbazolyl)benzene) host demonstrate a significant improvement of carrier radiative recombination efficiency, with the photoluminescence quantum yield increased by nearly ten times, which is rooted in the efficient energy transfer and type-I energy level alignment between [dppb]2Cu2I2 and mCP. Moreover, the charge-transporting mCP host can raise the carrier mobility of [dppb]2Cu2I2 films, thereby enhancing the charge transport and recombination. More importantly, this strategy enables a large-area prototype LED with a record-breaking area up to 81 cm2, along with a decent EQE of 10.02% and uniform luminance. It is believed these results represent an encouraging stepping stone to bring Cu halide-based LEDs from the laboratory toward commercial lighting and display panels.