Homogeneous Phase Distribution in Q-2D Perovskites via Co-Assembly of Spacer Cations for Efficient Light-Emitting Diodes

Synergistic Passivation via Amino Acid Derivative for Highly Efficient Quasi-2D Perovskite Green Light-Emitting Diode

Quasi two-dimensional (2D) perovskite light-emitting diodes (PeLEDs) have emerged as promising candidates for next-generation displays and solid-state lighting. However, defects in the perovskite films often hinder the device performance of quasi-2D PeLEDs, leading to nonradiative recombination and efficiency losses. Herein, we introduce a novel synergistic passivation strategy using an amino acid derivative of Boc-N3-Cbz-L-2,3-diaminopropionic acid (BNCDA), with multiple C═O and N-H functional groups to passivate defects and suppress ion migration in perovskite films. By incorporating the passivation agent into the precursor solution, we significantly reduced the defect density and enhanced radiative recombination. As a result, the optimized PeLEDs demonstrate a remarkable external quantum efficiency (EQE) of 22.6% and a maximum luminance of 57951 cd m-2 for 511 nm emission. Simultaneously, the optimal devices display superior spectral stability and an enhanced operation lifetime in ambient air. This work highlights the importance of the synergistic effect in effectively passivating defects in quasi-2D PeLEDs and provides an interesting way to select passivating molecules for fabricating high-performance PeLEDs for future display and lighting applications.

Promoting Phase Transition in Quasi-2D Perovskites For High-Performance Pure-Red LEDs

Layered quasi-two-dimensional (quasi-2D) halide perovskites have emerged as a promising platform for high-efficiency electroluminescence. Narrowing the multi-quantum well distribution and eliminating wide-bandgap 2D phases are crucial for achieving a flat energy landscape, minimizing energy loss, and ensuring high-color-purity emission. Here, it is demonstrated that solution-processed quasi-2D perovskite films with broad component distributions arise from an incomplete kinetic transition from low-n (n, quantum well thickness) to high-n phases. To address this, an acetate anion treatment strategy is proposed, which induces competitive coordination between the acetate anion, the bulky spacer cation, and the inorganic layer, thereby facilitating the insertion of octahedral precursor ions and promoting phase transition. This treatment results in quasi-2D films with enhanced color purity, efficient energy transfer, and high photoluminescence quantum yield. The fabricated perovskite light emitting diode (PeLED) exhibits an emission peak at 641 nm and a peak external quantum efficiency (EQE) of 25.3%, representing one of the most efficient pure-red PeLEDs. The strategy also showcases the versatility of quasi-2D films for different emission wavelengths.

Decoding the Role of Interface Engineering in Energy Transfer: Pathways to Enhanced Efficiency and Stability in Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) perovskites have emerged as a transformative platform for high-efficiency perovskite light-emitting diodes (PeLEDs), benefiting from their tunable quantum confinement, high photoluminescence quantum yields (PLQYs), and self-assembled energy funneling mechanisms. This review systematically explores interfacial energy transfer engineering strategies that underpin advancements in device performance. By tailoring phase composition distributions, passivating defects via additive engineering, and optimizing charge transport layers, researchers have achieved external quantum efficiencies (EQEs) exceeding 20% in green and red PeLEDs. However, challenges persist in blue emission stability, efficiency roll-off at high currents, and long-term operational durability driven by spectral redshift, Auger recombination, and interfacial ion migration. Emerging solutions include dual-cation/halogen alloying for bandgap control, microcavity photon management, and insulator-perovskite-insulator (IPI) architectures to suppress leakage currents. Future progress hinges on interdisciplinary efforts in multifunctional material design, scalable fabrication, and mechanistic studies of carrier-photon interactions. Through these innovations, quasi-2D PeLEDs hold promise for next-generation displays and solid-state lighting, offering a cost-effective and efficient alternative to conventional technologies.

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.

Manipulating Phase and Defect Distribution of Quasi-2D Perovskites via a Synergistic Strategy for Enhancing the Performance of Blue Light-Emitting Diodes

Quasi-two-dimensional (quasi-2D) mixed-halide perovskites are a requisite for their applications in highly efficient blue perovskite light-emitting diodes (PeLEDs) owing to their strong quantum confinement effect and high exciton binding energy. The pace of quasi-2D blue PeLEDs is hindered primarily by two factors: challenges in precisely managing the phase distribution and defect-mediated nonradiative recombination losses. Herein, we utilize 2,2-diphenylethylamine (DPEA+) with bulky steric hindrance to disturb the assembly process of a slender spacer host cation, 4-fluorophenylethylammonium (p-F-PEA+), enhancing phase distribution management in quasi-2D PeLEDs. The DPEA+ not only inhibits the small-n phase but also strengthens carrier transport and alleviates exciton quenching. In addition, dual additives─formamidine acetate (FAoAc) and guanidine thiocyanate (GASCN)─were incorporated to assist phase tailoring and passivation of remaining defects in the perovskite films. The C═O and SCN- groups can coordinate with Pb2+ to suppress the charge trap density and nonradiative recombination. As a result of employing a synergetic strategy for comprehensive phase distribution regulation and defect passivation, the optimized device achieves blue emission at 479 nm with a 5× improvement in external quantum efficiency (EQE) and a 13× increase in device operating stability. This synergetic strategy paves a simple route for phase management and defect passivation toward high-performance blue-emission PeLEDs.

Designing Robust Quasi-2D Perovskites Thin Films for Stable Light-Emitting Applications

Quasi-2D perovskite made with organic spacers co-crystallized with inorganic cesium lead bromide inorganics is demonstrated for near unity photoluminescence quantum yield at room temperature. However, light emitting diodes made with quasi-2D perovskites rapidly degrade which remains a major bottleneck in this field. In this work, It is shown that the bright emission originates from finely tuned multi-component 2D nano-crystalline phases that are thermodynamically unstable. The bright emission is extremely sensitive to external stimuli and the emission quickly dims away upon heating. After a detailed analysis of their optical and morphological properties, the degradation is attributed to 2D phase redistribution associated with the dissociation of the organic spacers departing from the inorganic lattice. To circumvent the instability problem, a diamine is investigated spacer that has both sides attached to the inorganic lattice. The diamine spacer incorporated perovskite film shows significantly improved thermal tolerance over maintaining a high photoluminescence quantum yield of over 50%, which will be a more robust material for lighting applications. This study guides designing quasi-2D perovskites to stabilize the emission properties.

Nonalloyed α-phase formamidinium lead triiodide solar cells through iodine intercalation

Formamidinium lead triiodide (FAPbI3) is considered the most promising composition for high-performing single-junction solar cells. However, nonalloyed α-FAPbI3 is metastable with respect to the photoinactive δ-phase. We have developed a kinetic modulation strategy to fabricate high-quality and stable nonalloyed α-FAPbI3 films, assisted by cogenetic volatile iodine intercalation and decalation. The intercalation of iodine facilitated the formation of corner-sharing Pb-I framework building blocks and reduced the kinetic barrier for α-FAPbI3 formation, whereas the iodine decalation improved the final perovskite film quality in terms of composition purity and overall homogeneity. Solar cells based on this nonalloyed α-FAPbI3 (free of other extrinsic composition ions) achieved a power conversion efficiency of >24%. The devices also exhibited excellent durability, retaining 99% of their original power conversion efficiency after operating for more than 1100 hours at 85° ± 5°C under illumination.

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.

Bilateral Embedded Anchoring via Tailored Polymer Brush for Large-Area Air-Processed Blue Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) that can be air-processed promises the development of displaying optoelectronic device, while is challenged by technical difficulty on both the active layer and hole transport layer (HTL) caused by the unavoidable humidity interference. Here, we propose and validate that, planting the polymer brush with tailored functional groups in inorganic HTL, provides unique bilateral embedded anchoring that is capable of simultaneously addressing the n phases crystallization rates in the active layer as well as the deteriorated particulate surface defects in HTL. Exemplified by zwitterionic polyethyleneimine-sulfonate (PEIS) in present study, its implanting in NiOx HTL offers abundant nuclei sites of amino and sulfonate groups that balance the growth rate of different n phases in quasi-2D perovskite films. Moreover, the PEIS effectively nailed the interfacial contact between perovskite and NiOx, and reduced the particulate surface defects in HTL, leading to the enhanced PLQY and stability of large-area blue perovskite film in ambient air. By virtue of these merits, present work achieves the first demonstration of the air-processed blue PeLEDs in large emitting area of 1.0 cm2 with peak external quantum efficiency (EQE) of 2.09 %, which is comparable to the similar pure-bromide blue PeLEDs fabricated in glovebox.

Homogenizing The Low-Dimensional Phases for Stable 2D-3D Tin Perovskite Solar Cells

2D-3D tin-based perovskites are considered as promising candidates for achieving efficient lead-free perovskite solar cells (PSCs). However, the existence of multiple low-dimensional phases formed during the film preparation hinders the efficient transport of charge carriers. In addition, the non-homogeneous distribution of low-dimensional phases leads to lattice distortion and increases the defect density, which are undesirable for the stability of tin-based PSCs. Here, mixed spacer cations [diethylamine (DEA+) and phenethylamine (PEA+)] are introduced into tin perovskite films to modulate the distribution of the 2D phases. It is found that compared to the film with only PEA+, the combination of DEA+ and PEA+ favors the formation of homogeneous low-dimensional perovskite phases with three octahedral monolayers (n = 3), especially near the bottom interface between perovskite and hole transport layer. The homogenization of 2D phases help improve the film quality with reduced lattice distortion and released strain. With these merits, the tin PSC shows significantly improved stability with 94% of its initial efficiency retained after storing in a nitrogen atmosphere for over 4600 h, and over 80% efficiency maintained after continuous illumination for 400 h.

Reconstruction and Solidification of Dion-Jacobson Perovskite Top and Buried Interfaces for Efficient and Stable Solar Cells

Quasi-two-dimensional (Q-2D) perovskites show great potential in the field of photonic and optoelectronic device applications. However, defects and local lattice dislocation still limit performance and stability improvement by nonradiative recombination, unpreferred phase distribution, and unbonded amines. Here, a low-temperature synergistic strategy for both reconstructing and solidifying the perovskite top and buried interface is developed. By post-treating the 1,4-phenylenedimethanammonium (PDMA) based (PDMA)MA4Pb5I16 films with cesium acetate (CsAc) before thermal annealing, a condensation reaction between R-COO- and -NH2 and ion exchange between Cs+ and MA+ occur. It converts the unbonded amines to amides and passivates uncoordinated Pb2+. Meanwhile, it adjusts film composition and improves the phase distribution without changing the out-of-plane grain orientation. Consequently, performance of 18.1% and much-enhanced stability (e.g., stability for photo-oxygen increased over 10 times, light-thermal for T90 over 4 times, and reverse bias over 3 times) of (PDMA)MA4Pb5I16 perovskite solar cells are demonstrated.

Reduced-Dimensional Perovskites: Quantum Well Thickness Distribution and Optoelectronic Properties

Reduced-dimensional perovskites (RDPs), a large category of metal halide perovskites, have attracted considerable attention and shown high potential in the fields of solid-state displays and lighting. RDPs feature a quantum-well-based structure and energy funneling effects. The multiple quantum well (QW) structure endows RDPs with superior energy transfer and high luminescence efficiency. The effect of QW confinement directly depends on the number of inorganic octahedral layers (QW thickness, i.e., n value), so the distribution of n values determines the optoelectronic properties of RDPs. Here, it is focused on the QW thickness distribution of RDPs, detailing its effect on the structural characteristics, carrier recombination dynamics, optoelectronic properties, and applications in light-emitting diodes. The reported distribution control strategies is also summarized and discuss the current challenges and future trends of RDPs. This review aims to provide deep insight into RDPs, with the hope of advancing their further development and applications.

Restraint of Nonradiative Recombination via Modulation of n-Phase Distribution through Interfacial Lithium Salt Insertion for High-Performance Pure-Blue Perovskite LEDs

Quasi-two-dimensional perovskite has been widely used in blue perovskite light-emitting diodes. However, the performance of these devices is still hampered by random phase distribution, nonradiative recombination, and imbalanced carrier transport. In this work, an effective strategy is proposed to mitigate these limitations by inserting lithium salts at the interfaces between the hole transport layer (HTL) and the perovskite layer. The perovskite film on the inserted Li2CO3 layer exhibits reasonable n-value redistribution, which leads to the repressive nonradiation recombination and enhanced carrier transport. Moreover, the inserted Li2CO3 layer also improves the electrical conductivity of PEDOT:PSS and hinders indium ion diffusion from the PEDOT:PSS layer to the perovskite film, which inhibits exciton quenching and nonradiative recombination loss at the HTL/perovskite interface. Taking advantage of these merits, we have successfully fabricated efficient pure-blue PeLEDs with an external quantum efficiency of 6.2% at 472 nm and a luminance of 726 cd cm-2. The restraint of nonradiative recombination at the interface offers a promising approach for efficient pure-blue PeLEDs.

Dual-ligand quasi-2D perovskites with chiral-induced spin selectivity for room temperature spin-LEDs

Spin-LEDs have been a central topic in semiconductor spintronics research and represent a promising avenue for advanced optoelectronic devices and applications. The future advancements of spin-LEDs will undoubtedly hinge on the generation and manipulation of spin-polarized population at room temperature. In this research, we elucidate the development of room-temperature spin-LEDs using quasi-2D perovskites, based on the chiral-induced spin selectivity (CISS) effect. During the carrier transfer from the chiral n2 phase to the randomly oriented high-n phase caused by the bandgap gradient distribution, CISS works to generate non-equilibrium spin population, leading to room-temperature spin-polarized fluorescence. A spin-polarization of ∼93% is observed for the films. Finally, we realize spin-LEDs at room temperature, exhibiting a |gCP-EL| value of 0.05 and an EQE of 3.8%. This work highlights the potential of integrating dual ligands to optimize the phase distribution and crystalline orientation in quasi-2D films to achieve efficient CISS for spin-LED applications.

Energy Transfer-Dominated Quasi-2D Blue Perovskite Light-Emitting Diodes

The bromide-chloride mixed quasi-two-dimensional (2D) perovskite, with a natural quantum well structure and tunable exciton binding energy, has gained significant attention for high-performance blue perovskite light-emitting diodes (PeLEDs). However, the relative importance of having a low trap state density or efficient exciton transfer for high-efficiency electroluminescence (EL) performance remains elusive. Here, two molecules with the benzoic acid group, sodium 4-fluorobenzoate (SFB) and 3,5-dibromobenzoic acid (DBA), are used to modulate the phase distribution and trap state to explore the effect between energy transfer and defect passivation. As a result, when the n = 1 phase is inhibited in both films, the DBA@SFB-modified perovskite films achieve a higher photoluminescence quantum yield (PLQY) than the SFB-modified perovskite films due to effective defect passivation. However, DBA@SFB-modified PeLEDs exhibit lower external quantum efficiency (EQE) compared to SFB-modified PeLEDs due to the poor exciton transfer between the low-dimensional phase. This demonstrates that passivation strategies may enhance photoluminescence through reducing nonradiative recombination, but the effect of phase distribution is pivotal for EL performance by efficient energy transfer in quasi-2D perovskites. Femtosecond time-resolved transient absorption measurements confirm the fastest carrier dynamics in SFB-modified perovskite films, further corroborating the above result. This work provides useful information about phase modulation and defect passivation for high-efficiency blue quasi-2D PeLEDs.

High-Performance All-Inorganic Architecture Perovskite Light-Emitting Diodes Based on Tens-of-Nanometers-Sized CsPbBr3 Emitters in a Carrier-Confined Heterostructure

Developing green perovskite light-emitting diodes (PeLEDs) with a high external quantum efficiency (EQE) and low efficiency roll-off at high brightness remains a critical challenge. Nanostructured emitter-based devices have shown high efficiency but restricted ascending luminance at high current densities, while devices based on large-sized crystals exhibit low efficiency roll-off but face great challenges to high efficiency. Herein, we develop an all-inorganic device architecture combined with utilizing tens-of-nanometers-sized CsPbBr3 (TNS-CsPbBr3) emitters in a carrier-confined heterostructure to realize green PeLEDs that exhibit high EQEs and low efficiency roll-off. A typical type-I heterojunction containing TNS-CsPbBr3 crystals and wide-bandgap Cs4PbBr6 within a grain is formed by carefully controlling the precursor ratio. These heterostructured TNS-CsPbBr3 emitters simultaneously enhance carrier confinement and retain low Auger recombination under a large injected carrier density. Benefiting from a simple device architecture consisting of an emissive layer and an oxide electron-transporting layer, the PeLEDs exhibit a sub-bandgap turn-on voltage of 2.0 V and steeply rising luminance. In consequence, we achieved green PeLEDs demonstrating a peak EQE of 17.0% at the brightness of 36,000 cd m-2, and the EQE remained at 15.7% and 12.6% at the brightness of 100,000 and 200,000 cd m-2, respectively. In addition, our results underscore the role of interface degradation during device operation as a factor in device failure.

Phase Control and Singlet Energy Transfer Enabled by Trimethylamine Modified Boron Dipyrromethene for Stable CsPbBr3 Quantum Wells

The phase distribution and organic spacer cations play pivotal roles in determining the emission performance and stability of perovskite quantum wells (QWs). Here, we propose a universal molecular regulation strategy to tailor phase distribution and enhance the stability of CsPbBr3 QWs. The capability of sterically hindered ligands with formidable surface binding groups is underscored in directing CsPbBr3 growth and refining phase distribution. With trimethylamine modified boron dipyrromethene (BDP-TMA) ligand as a representative, the BDP-TMA driven can precisely control phase distribution and passivate defects of CsPbBr3 . Notably, BDP-TMA acts as a co-spacer organic entity in obtained BDP-TMA-CsPbBr3 , facilitating efficient singlet energy transfer and tailoring the luminescence to produce a distinctive bluish-white emission. The BDP-TMA-CsPbBr3 demonstrates significant phase stability under water exposure, light irradiation, and moderate temperature. Interestingly, BDP-TMA-CsPbBr3 exhibits the thermally-induced dynamic fluorescence control at elevated temperatures, which can be achieved feasible for advanced information encryption. This discovery paves the way for the exploration of perovskite QWs in applications like temperature sensing, anti-counterfeiting, and other advanced optical smart technologies.

Carrier Transport in 2D Hybrid Organic-Inorganic Perovskites: The Role of Spacer Molecules

Two-dimensional organic-inorganic hybrid perovskites (2D HOIPs) have been widely used for various optoelectronics applications owing to their excellent photoelectric properties. However, the selection of organic spacer cations is mostly qualitative without quantitative guidance. Meanwhile, the fundamental mechanism of the carrier transport across the organic spacer layer is still unclear. Here, by using the first-principles nonadiabatic molecular dynamics (NAMD) method, we have studied the transport process of excited carriers between 2D HOIPs separated by a spacer cation layer in real time at atomic levels. We find that the excited electrons and holes can transfer from single-inorganic-layer 2D HOIP to bi-inorganic-layer 2D HOIP on a subpicosecond to picosecond scale. Moreover, we have developed a new method to capture the electron-hole interaction in the frame of NAMD. This work provides a promising direction to design new materials toward high-performance optoelectronics.

Investigation of the Role of K2SO4 Electrolyte in Hole Transport Layer for Efficient Quasi-2D Perovskite Light-Emitting Diodes

Quasi-two-dimensional (2D) perovskite light-emitting diodes are promising light sources for color display and lighting. However, poor carrier injection and transport between the bottom hole transport layer (HTL) and perovskite limit the device performance. Here we demonstrate a simple and effective way to modify the HTL for enhancing the performance of perovskite light-emitting diodes (PeLEDs). An electrolyte K2SO4 is used to mix with poly(3,4-ethylenedioxythiophene):poly(styrene sulfonate) (PEDOT:PSS) as the hole transport layer. The K+ doping helped the quasi-2D perovskite phases grow vertically along the interface of the PEDOT:PSS, fine-modulate the phase distribution, and simultaneously reduce the defect density of quasi-2D perovskites. It also significantly reduced the exciton quenching and injection barrier at PEDOT:PSS and quasi-2D perovskite interface. The optimized green PeLEDs with the K2SO4 doped PEDOT:PSS HTL showed a maximum luminance of 17185 cd/m2 which is almost 4.7 times brighter than the control one, with a maximum external quantum efficiency of 18.64%.

Impact of Alkyl Chain Length on the Formation of Regular- and Reverse-Graded Quasi-2D Perovskite Thin Films

Crystallization of low-dimensional perovskites is a complex process that leads to multidimensional films comprising two-dimensional (2D), quasi-2D, and three-dimensional (3D) phases. Most quasi-2D perovskite films possess a regular gradient with 2D phases located at the bottom of the film and 3D phases at the top. Recently, multiple studies have reported reverse-graded perovskite films, where the location of the 2D and 3D structures is inverted. The underlying reasons for such a peculiar phase distribution are unclear. While crystallization of regular-graded quasi-2D perovskites has been described as starting with 3D phases from the liquid-air interface, the film formation of reverse-graded films has not been investigated yet. Here, we examine the impact of the alkyl chain length on the formation of regular- and reverse-graded perovskites using n-alkylammonium ions. We find that long alkyl chains reverse the phase distribution gradient. By combining photoluminescence spectroscopy with in situ optical absorption measurements, we demonstrate that crystallization starts at the liquid-N2 interface, though as 3D phases for short-chain n-alkylammonium ions and as quasi-2D phases for long chains. We link this behavior to enhanced van der Waals interactions between long-chain n-alkylammonium ions in polar solvents and their tendency to accumulate at the liquid-N2 interface, creating a concentration gradient along the film thickness.

Modulation Phase Distribution of Ruddlesden-Popper Quasi-2D Perovskites with a Similarly Spaced Dion-Jacobson Phase

Quasi-two-dimensional (quasi-2D) perovskites exhibit excellent performance when applied to light-emitting diodes (LEDs). However, quasi-2D perovskite films generally have nonuniform n phases and irregular internal crystal structures, which degrade the device's performance. Here, we propose using a Dion-Jacobson (DJ)-type organic spacer to modulate the phase distribution of the Ruddlesden-Popper (RP) quasi-2D perovskite. A DJ-type organic spacer cation, 1.6-hexamethylenediamine (HDABr2), was introduced into the perovskite as the second spacer cation with propylamine hydrobromide (PABr). As DJ-type and RP-type perovskites have similar spacings, RP-DJ style does not cause a chaotic crystalline structure; instead, it modulates the perovskite crystallization and narrows the phase distribution. In parallel, there is a substantial improvement in the maximum luminance, current efficiency, external quantum efficiency, and device stability of the quasi-2D perovskite LEDs. This work provides a novel concept for combining the organic spacer cations for quasi-2D perovskites.