Interfacial Potassium-Guided Grain Growth for Efficient Deep-Blue Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) are emerging candidates for the applications of solution-processed full-color displays. However, the device performance of deep-blue PeLED still lags far behind that of their red and green counterparts, which is largely limited by low external quantum efficiency (EQE) and poor operational stability. Here, a facile and reliable crystallization strategy for perovskite grains is proposed, with improved deep-blue emission through rational interfacial engineering. By modifying the substrate with potassium cation (K⁺) as the supplier of heterogeneous nucleation seeds, the interfacial K⁺-guided grain growth is realized for well-packed perovskite assemblies with high surface coverage and the controlled crystal orientation, leading to the enhanced radiative recombination and hole-transport capabilities. Synergistical boost in device performance is achieved for deep-blue PeLEDs emitting at 469 nm with a peak EQE of 4.14%, a maximum luminance of 451 cd m^–2, and spectrally stable color coordinates of (0.125, 0.076) that matches well with the National Television System Committee (NTSC) standard blue.     

Highly Efficient Blue Light-Emitting Diodes Based on Perovskite Film with Vertically Graded Bandgap and Organic Grain Boundary Passivation Shells

Metal halide perovskite materials have emerged as a promising class of semiconductors for high-performance optoelectronic applications, particularly for light-emitting diodes (LEDs), due to their high quantum efficiency, facile color tunability, narrow emission line widths, as well as cost-effectiveness. Despite the great successes on green and red perovskite LEDs (PeLEDs), the external quantum efficiency (EQE) of blue PeLEDs still lags far behind that of green and red counterparts. Here, wavelength tunable pure and deep blue PeLEDs with high EQE are presented, achieving 17.5% and 10.8% for emission wavelengths of 472 and 461 nm, respectively. The wavelength tenability and high EQE are attributed to the unique vertically graded bandgaps and grain boundary organic shells in the perovskite films. The results demonstrate a significant performance improvement in blue PeLEDs, provide a novel route to fabricate high-performance pure and deep blue PeLEDs that can match the performance of the green and red PeLEDs for future lighting and display applications.     

Interfacial Nucleation Seeding for Electroluminescent Manipulation in Blue Perovskite Light-Emitting Diodes

Efficient and stable blue emission of perovskite light-emitting diodes (PeLEDs) is a requisite toward their potential applications in full-color displays and solid-state lighting. Rational manipulation over the entire electroluminescence process is promising to break the efficiency limit of blue PeLEDs. Herein, a facile device architecture is proposed to achieve efficient blue PeLEDs for simultaneously reducing the energetic loss during electron-photon conversion and boosting the light outcoupling. Effective interfacial engineering is employed to manipulate the perovskite crystallization nucleation, enabling highly compact perovskite nanocrystal assemblies and suppressing the trap-induced carrier losses by means of interfacial hydrogen bonding interactions. This strategy contributes to a high external quantum efficiency (EQE) of 12.8% for blue PeLEDs emitting at 486 nm as well as improved operational stability. Moreover, blue PeLEDs reach a peak EQE of 16.8% with the incorporation of internal outcoupling structures for waveguided light, which can be further raised to 27.5% by integrating a lens-based structure for substrate-mode light. These results verify the validity of this strategy in producing efficient and stable blue PeLEDs for practical applications.     

Suppressing Ion Migration of Mixed-Halide Perovskite Quantum Dots for High Efficiency Pure-Red Light-Emitting Diodes

Perovskite-based light-emitting diodes (PeLEDs) with a mixed halide composition can be used to obtain the “pure red” emission, i.e., in the 620–650 nm range, required for high-definition displays. However, fast halide ion migration induces phase separation in these materials under electric fields, resulting in poor spectral stability and low efficiency. Herein, a method for producing mixed halide CsPbI_3-xBr_x quantum dots (QDs) is reported in which ion migration is suppressed. The mixed halide composition is first achieved by anion exchange between CsPbI₃ QDs and hydrobromic acid (HBr), during that the bromine ions efficiently passivate the iodine vacancies of the QDs. The original oleic acid ligands are then exchanged for 1-dodecanethiol (1-DT), which suppresses halide ion migration via the strong binding of the sulfhydryl group with the QD surface. PeLEDs based on these QDs exhibit a pure-red electroluminescence (EL) peak at 637 nm, a maximum external quantum efficiency (EQE) of 21.8% with an average value of 20.4%, a peak luminance of 2653 cd m⁻², and low EQE decease with increasing luminance. The EL spectrum of these devices is stable even at 6.7 V and they have an EQE half-life of 70 min at an initial luminance of 150 cd m⁻².     

Manipulating Ionic Behavior with Bifunctional Additives for Efficient Sky-Blue Perovskite Light-Emitting Diodes

Perovskite Light-emitting diodes (PeLEDs) have emerged as a promising technique for future high-definition displays due to their outstanding electroluminescent characters. However, the development of blue PeLEDs toward practical applications is seriously hindered by their inferior performance, which mainly arises from the detrimental halide ionic behavior and thus severe nonradiative recombination in mixed-halide blue perovskite materials. Herein, efficient sky-blue PeLEDs featuring spectrally stable emission at 483 nm are realized by employing bifunctional passivators of Lewis-base benzoic acid anions and alkali metal cations to simultaneously passivate the under-coordinated lead atoms and suppress halide ion migration. A decent external quantum efficiency (EQE) of 16.58% and a maximum EQE of 18.65% are achieved, which is further boosted to 28.82% through the optical outcoupling enhancement. This work demonstrates unique insight into the generality and individuality of this category of benzoates and puts forward a feasible guidance in choosing appropriate additives for efficient perovskite materials.     

Enhanced performance of spectra stable blue perovskite light-emitting diodes through Poly(9-vinylcarbazole) interlayer incorporation

Since the emergence of organic-inorganic hybrid perovskites, the development of perovskite light-emitting diodes (PeLEDs) with green/red emission have made great progress, and the corresponding external quantum efficiency (EQE) has exceeded 20%. However, the research progress of blue-emitting PeLED still has certain challenges. In this article, a multi-cation per-bromine perovskite film is prepared by introducing polymer molecules poly(9-vinylcarbazole) (PVK) in an anti-solvent (chloroform). When the concentration of PVK is optimized to 0.1 mg/mL, a smooth, dense, high-quality film with photoluminescence quantum efficiency (PLQY) up to 20.70% is obtained. The introduction of PVK can assist the formation of perovskite films for interface modification via surface defect passivation. The optimized blue PeLED has a maximum brightness of 3136 cd/m² and a maximum EQE of 3.49% at 488 nm. More importantly, the optimized blue PeLED has excellent color stability under high applied voltage up to 12 V or continuous operation.     

Synthesis of 0D Manganese-Based Organic–Inorganic Hybrid Perovskite and Its Application in Lead-Free Red Light-Emitting Diode

Lead-based perovskite light-emitting diodes (PeLEDs) have exhibited excellent purity, high efficiency, and good brightness. In order to develop nontoxic, highly luminescent metal halide perovskite materials, tin, copper, germanium, zinc, bismuth, and other lead-free perovskites have been developed. Here, a novel 0D manganese-based (Mn-based) organic–inorganic hybrid perovskite with the red emission located at 629 nm, high photoluminescence quantum yield of 80%, and millisecond level triplet lifetime is reported. When applied as the emissive layer in the PeLEDs, the maximum recording brightness of devices after optimization is 4700 cd m⁻², and the peak external quantum efficiency is 9.8%. The half-life of the device reaches 5.5 h at 5 V. The performance and stability of Mn-based PeLEDs are one order of magnitude higher than those of other lead-free PeLEDs. This work clearly shows that the Mn-based perovskite will provide another route to fabricate stable and high-performance lead-free PeLEDs.     

H2O treatment-induced uniform NiOX interfacial layer boosting brightness and light-emitting efficiency of blue perovskite electroluminescence

The reported NiO_x interfacial layers in blue perovskite light-emitting diodes (PeLEDs) usually require high-temperature annealing and complex interface modification. Herein, we report a kind of uniform NiO_x anode interfacial layer induced by H₂O treatment, which effectively enhances the brightness and light-emitting efficiency of blue PeLEDs simultaneously. Compared to the as-prepared NiO_x anode interfacial layer, H₂O treatment renders uniform and pinhole-free NiO_x morphology. The solution-processed perovskite blue emissive layer prepared atop the H₂O-treated NiO_x interfacial layer demonstrates enhanced photoluminescent property and superior morphology with low trap density. The blue PeLEDs employing H₂O-treated NiO_x as anode interfacial layer show a maximum luminance of 9052 cd/m² and a maximum external quantum efficiency (EQE) of 1.80%, whereas the control device based on the as-prepared NiO_x anode interfacial layer merely exhibits a maximum luminance of 3850 cd/m² and an EQE of 0.88%, leading to about 135% and 104% increase in brightness and efficiency, respectively. The PeLEDs emit pure blue light with emission peak located at 482 nm and demonstrate superior spectral stability under different driving voltages and operating time.     

Green Perovskite Light-Emitting Diodes with 200 Hours Stability and 16% Efficiency: Cross-Linking Strategy and Mechanism

According to the thinner emitting layer and stronger electric field in perovskite light-emitting diodes (PeLEDs) than those in perovskite solar cells, the strong electric-field-driven ion-migration is a key issue for the operational stability of PeLEDs. Here, a methylene-bis-acrylamide cross-linking strategy is proposed to both passivate defects and suppress ion-migration with an emphasis on the suppressing mechanism via in situ investigations. As typical results, in addition to the enhanced external quantum efficiency (EQE, 16.8%), PeLEDs exhibit preferable operational stability with a half lifetime (T₅₀) of 208 h under continuous operation with an initial luminance of 100 cd m⁻². Moreover, the EQE of cross-linked LEDs can maintain above 15% during 25 times scanning as the devices are measured every 4 days. To the authors’ knowledge, this is the highest stability published until now for high-efficiency PeLEDs with EQE over 15%. The in situ/ex situ mechanism investigation demonstrates that such cross-linking increases binding energy from 0.54 to 0.92 eV and activation energy from 0.21 to 0.5 eV. Hence, it suppresses ligands breaking away and ion migration, which prevents ions from moving inside and across crystals. The proposed cross-linking passivation strategy thus provides an effective methodology to fabricate stable perovskites-based photoelectric devices.     

High-Performance Perovskite-Based Blue Light-Emitting Diodes with Operational Stability by Using Organic Ammonium Cations as Passivating Agents

Blue emissive perovskites can be prepared by incorporating chlorine into bromine-based perovskites to tune their bandgap. However, mixed-halide perovskites exhibit intrinsic phase instability, particularly under electrical potential, owing to halide migration. To achieve high-performance blue perovskite-based light-emitting diodes (PeLEDs) with operational stability, organic ammonium cations are used for passivating the anionic defects of the CsPbBr₂Cl film. Diphenylpropylammonium chloride (DPPACl), used as a passivating agent, successfully prevents the spectral instability of blue PeLEDs by passivating the Cl⁻ vacancies. Consequently, the blue PeLED prepared with this passivating agent delivers excellent device performance with a maximum external quantum efficiency of 3.03%. Moreover, upon tuning the DPPACl concentration, the PeLED emits stably in the deep-blue spectral region (464 nm) with a half-life time of 420 s. Thus, the use of organic ammonium cation as a passivating agent is an effective strategy for developing high-performance blue PeLEDs with operational stability.     

An Easily Developed Difunctional Molecule Enabling Highly Efficient and Stable Light-Emitting Diodes

The surface treatment for solution-processed perovskite films using molecular passivation agents has been reported to be critical for improving the performance of perovskite light-emitting diodes (PeLEDs). Generally, most studies emphasized the binding effect between passivation molecules and perovskite surface, while halide perovskites are dominated by multiple defects and need more comprehensive passivation, which is often neglected. Here, a molecule of 5-ammonium valeric acid trifluoroacetate (5-AVATFA) with multi-functional groups is rationally developed to modify the interface of advanced PeLEDs. Combining experimental and density functional theory analysis, the synergism effects of reduced surface defects and increased steric hindrance of 5-AVATFA, which can greatly suppress the ion migration of PeLEDs, are demonstarated. Because of the passivation effect of multi-functional 5-AVATFA, an optimal device with an external quantum efficiency of 22.32%, a radiance of 558.46 W sr⁻¹ m⁻², and an extended half-lifetime of 103.3 h is obtained.     

Minimizing Energy Barrier in Intermediate Connection Layer for Monolithic Tandem WPeLEDs with Wide Color Gamut

Perovskite light-emitting diodes (PeLEDs) show promising prospects in the wide color gamut display owing to their ultra-narrow full width at half maximum (FWHM). However, up to now, all perovskite white LEDs integrated by standard red, green, and blue perovskite emitters, namely, monolithic white PeLEDs (WPeLEDs), have been rarely reported, owing to facing some issues, e.g., solvent incompatibility in solution technique, ion exchange, and energy transfer between different emission centers. Herein, centered on these issues, an optimal intermediate connection layer (ICL) of Po-T2T/LiF/Ag/HAT-CN/MoO₃ is adopted to successfully develop monolithic tandem multicolor PeLEDs and WPeLEDs for the first time. The multicolor PeLEDs can achieve the best external quantum efficiency of 1.8% and the highest luminance of 4844 cd m⁻². Besides, the red/green/blue (R/G/B) monolithic tandem WPeLED shows a standard white International Commission on Illumination coordinate of (0.33, 0.33) and achieves an extremely wide color gamut reaching  National Television Standards Committee of 130%. This study is the first to realize the standard R/G/B co-electroluminescence in a monolithic perovskite device and offers a feasible strategy for developing wide-color gamut perovskite displays.     

Pure Blue Electroluminescence by Differentiated Ion Motion in a Single Layer Perovskite Device

Blue electroluminescence is highly desired for emerging light-emitting devices for display applications and optoelectronics in general. However, saturated, efficient, and stable blue emission has been challenging to achieve, particularly in mixed-halide perovskites, where intrinsic ion motion and halide segregation compromises spectral purity. Here, CsPbBr_3−xCl_x perovskites, polyelectrolytes, and a salt additive are leveraged to demonstrate pure blue emission from single-layer light-emitting electrochemical cells (LECs). The electrolytes transport the ions from salt additives, enhancing charge injection and stabilizing the inherent perovskite emissive lattice for highly pure and sustained blue emission. Substituting Cl into CsPbBr₃ tunes the perovskite luminescence from green through blue. Sky blue and saturated blue devices produce International Commission on Illumination coordinates of (0.105, 0.129) and (0.136, 0.068), respectively, with the latter meeting the US National Television Committee standard for the blue primary. Likewise, maximum luminances of 2900 and 1000 cd m⁻², external quantum efficiencies (EQEs) of 4.3% and 3.9%, and luminance half-lives of 5.7 and 4.9 h are obtained for sky blue and saturated blue devices, respectively. Polymer and LiPF₆ inclusion increases photoluminescence efficiency, suppresses halide segregation, induces thin-film smoothness and uniformity, and reduces crystallite size. Overall, these devices show superior performance among blue perovskite light-emitting diodes (PeLEDs) and general LECs.     

Minimizing Optical Energy Losses for Long-Lifetime Perovskite Light-Emitting Diodes

Regardless of the rapid advance on perovskite light-emitting diodes (PeLEDs), the lack of long-term operational stability hinders the practicality of this technology. Particularly, thermal management is indispensable to control the Joule heating induced by charge transport and parasitic re-absorption of internally confined photons. Herein, a synergetic device architecture is proposed for minimizing the optical energy losses in PeLEDs toward high efficiency and long lifetime. By adopting a carefully modified perovskite emitter in combination with an improved light outcoupling structure, red PeLEDs emitting at 666 nm achieve a peak external quantum efficiency of 21.2% and an operational half-lifetime of 4806.7 h for an initial luminance of 100 cd m^-2. The enhanced light extraction from trapped modes can efficiently reduce the driving current and suppress optical energy losses in PeLEDs, which in turn ameliorate the heat-induced device degradation during operation. This work paves the way toward high-performance PeLEDs for display and lighting applications in the future.     

Efficient All-Perovskite White Light-Emitting Diodes Made of In Situ Grown Perovskite-Mesoporous Silica Nanocomposites

Metal halide perovskite quantum dots (QDs) have emerged as potential materials for high brightness, wide color gamut, and cost-effective backlight emission due to their high photoluminescence quantum yields, narrow emission linewidths, and tunable bandgaps. Herein, CsPbX₃/SBA-15 nanocomposites are prepared with outstanding optical properties and high stability through an in situ growth strategy using mesoporous silica particles. According to finite-difference time-domain simulations, the mesoporous structure provides a strong waveguide effect on perovskite QDs and the uniform dispersion suppresses reabsorption losses, improving the overall photoconversion efficiency of perovskite QDs. The as-fabricated perovskite monochromatic light-emitting diode (LED) has a maximum luminous efficiency of 183 lm W⁻¹, which is the highest for monochromatic perovskite LEDs reported to date. A further benefit of this work is that the white devices, which combine the green and red perovskite nanocomposites with commercial blue LED, exhibit a high luminous efficiency of 116 lm W⁻¹ and a wide color gamut (125% for NTSC and 94% for Rec. 2020) with coordinates of (0.33,0.31).     

Blue perovskite LEDs

Metal halide perovskite light-emitting diodes (PeLEDs)show great potential in ultra-high-definition displays,due to their narrowband emission,wide color gamut (～140％),and cost-effective solution processability[1]M.Thanks to scientists' tremendous efforts,the external quantum efficiencies (EQEs)for the state-of-the-art PeLEDs emitting near-infrared and green light have reached 21.6％[2] and 23.4％[3],respectively.However,blue PeLEDs,as one of the essential technologies for perovskite-based high-resolution monitors and white light-ing,are still inferior to their red and green counterparts.Blue emission is usually achieved by using dimensional engineer-ing (quantum confinement) or composition engineering(mixed halides,e.g.,mixed Br/Cl) strategies.For example,quasi-two-dimensional (2D) perovskites,nanocrystals (e.g.,quantum dots,QDs) or nanoplates,give blue emission due to quantum confinement effects.However,achieving pure-blue(465-475 nm) and deep-blue (420-465 nm) light from quasi-2D perovskites is challenging[4],while ultra-small QDs and nanoplates suffer from high surface trap density and poor sta-bility[5].For PeLEDs based on mixed Br/Cl perovskites,the emis-sion peak can be tuned easily,but these perovskites face the disadvantages of phase separation and deep energy-level Cl vacancies[4].     

Highly Efficient Quasi 2D Blue Perovskite Electroluminescence Leveraging a Dual Ligand Composition

Perovskite light-emitting diodes (PeLEDs) are advancing because of their superior external quantum efficiencies (EQEs) and color purity. Still, additional work is needed for blue PeLEDs to achieve the same benchmarks as the other visible colors. This study demonstrates an extremely efficient blue PeLED with a 488 nm peak emission, a maximum luminance of 8600 cd m⁻², and a maximum EQE of 12.2% by incorporating the double-sided ethane-1,2-diammonium bromide (EDBr₂) ligand salt along with the long-chain ligand methylphenylammonium chloride (MeCl). The EDBr₂ successfully improves the interaction between 2D perovskite layers by reducing the weak van der Waals interaction and creating a Dion–Jacobson (DJ) structure. Whereas the pristine sample (without EDBr₂) is inhibited by small stacking number (n) 2D phases with nonradiative recombination regions that diminish the PeLED performance, adding EDBr₂ successfully enables better energy transfer from small n phases to larger n phases. As evidenced by photoluminescence (PL), scanning electron microscopy (SEM), and atomic force microscopy (AFM) characterization, EDBr₂ improves the morphology by reduction of pinholes and passivation of defects, subsequently improving the efficiencies and operational lifetimes of quasi-2D blue PeLEDs.     

Suppressing Ion Migration Enables Stable Perovskite Light‐Emitting Diodes with All‐Inorganic Strategy

Stability issue is one of the major concerns that limit emergent perovskite light‐emitting diodes (PeLEDs) techniques. Generally, ion migration is considered as the most important origin of PeLEDs degradation. In this work, an all‐inorganic device architecture, LiF/perovskite/LiF/ZnS/ZnSe, is proposed to address this imperative problem. The inorganic (Cs_1?xRb_x)_1?yK_yPbBr₃ perovskite is optimized with achieving a photoluminescence quantum yield of 67%. Depth profile analysis of X‐ray photoelectron spectroscopy indicates that the LiF/perovskite/LiF structure and the ZnS/ZnSe cascade electron transport layers significantly suppress the electric‐field‐induced ion migrations of the perovskite layers, and impede the diffusion of metallic atoms from cathode into perovskites. The as‐prepared PeLEDs display excellent shelf stability (maintaining 90% of the initial external quantum efficiency [EQE] after 264 h) and operational stability (half‐lifetime of about 255 h at an initial luminance of 120 cd m^?2). The devices also exhibit a maximum brightness of 15 6155 cd m^?2 and an EQE of 11.05%.     

Air-Processed Blue Perovskite Light-Emitting Diodes Enabled by Manipulation of Adsorbed-Moisture-Dominated Crystallization Kinetics

The fabrication of blue perovskite light-emitting diodes (PeLEDs) in air conditions promises to liberate the manipulation procedures from the protection of inert atmosphere in the glovebox, which will remarkably promote the commercialization proceeding of perovskite-based optoelectronic devices in display applications. However, achieving air-processed blue PeLEDs in the interference of moisture meets great challenges in crystallization kinetics control. Herein, it is proposed that substrate-adsorbed moisture dominates the perovskite crystallization kinetics during the fabrication in air, and the limited moisture from nonhygroscopic substrate inhibits the nucleation of the large-n phase and allows the growth of the small-n phase, thus yielding blue quasi-2D perovskite films in a wide moisture range of 10–50% relative humidity. Then, air-processed blue PeLEDs are successfully achieved for the first time, showing a brightness of 968 cd m⁻², external quantum efficiency of 2.54% at stable peak emission of 483 nm, as well as an outstanding operating stability of 546 s at a peak brightness of 45 cd m⁻², which are favorably competitive with PeLEDs fabricated in the glovebox. This work provides a guideline for air-processed blue PeLEDs fabrication, which paves the way for air-processed PeLEDs in further application of commercialization display.     

Highly efficient quasi-two dimensional perovskite light-emitting diodes by phase tuning

Tetraphenylphosphonium chloride (TPPCl) is used as an additive in the antisolvent for preparing the quasi-two Dimensional (quasi-2D) perovskite film. This strategy is not only beneficial for the morphology formation but also the phase tuning of the quasi-2D perovskite film. Highly efficient and stable perovskite light-emitting diodes (PeLEDs) were achieved with the maximum luminance of 35,000 cd/m², the maximum current efficiency of 48.0 cd/A and the maximum external quantum efficiency (EQE) of 12.42%. Due to the reduced exciton quenching rate, improved charge carrier injection and transport ability, the electroluminescent performance of the TPPCl-based PeLEDs has been enhanced.