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Device performance of distribution controlled quasi-2D perovskite LEDs a Device architecture. PVSK indicates the quasi-2D perovskites investigated in this work. b, c Current density-voltage-radiance (J-V-R) curves (b) and EQE characteristic (c) of quasi-2D perovskite LEDs. d EL spectra under forward biases of 4, 5, 6, 7 and 8 V. Inset is a photograph of a working device. e Histogram of EQEs measured from 70 devices, which gives an average value of 22.9% and a relative standard deviation of 6.9%. f Simulated fractional power distribution in the LED structure as a function of emission wavelength. g Operational stability measurement of quasi-2D perovskite LEDs based on different ligands without encapsulation, performed in nitrogen filled glove box at a constant current density of 0.1 mA/cm². h Operational stability of PPT device under various current densities.
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Electroluminescence efficiencies and stabilities of quasi-two-dimensional halide perovskites are restricted by the formation of multiple-quantum-well structures with broad and uncontrollable phase distributions. Here, we report a ligand design strategy to substantially suppress diffusion-limited phase disproportionation, thereby enabling better pha...
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Citations
... The corresponding photoluminescence centre was about 653 nm (Extended Data Fig. 2a). At higher molar ratios, a blueshift was observed in the main peak, but this was accompanied by a distinct high-energy peak, which we attribute to the formation of several phases with inefficient energy transfer [34][35][36] . To optimize the energy cascade channels to achieve pure-red photoluminescence emission with enhanced luminous efficiency, we took advantage of the synergistic effect from another two ligands, α-methylbenzyl-ammonium (MBA) and 1-methyl-3-phenylpropyl-ammonium (MPPA), whose steric hindrances and electrical properties are obviously distinct (inset in Fig. 1e). ...
Light-emitting diodes (LEDs) based on metal halide perovskites (PeLEDs) with high colour quality and facile solution processing are promising candidates for full-colour and high-definition displays1–4. Despite the great success achieved in green PeLEDs with lead bromide perovskites⁵, it is still challenging to realize pure-red (620–650 nm) LEDs using iodine-based counterparts, as they are constrained by the low intrinsic bandgap⁶. Here we report efficient and colour-stable PeLEDs across the entire pure-red region, with a peak external quantum efficiency reaching 28.7% at 638 nm, enabled by incorporating a double-end anchored ligand molecule into pure-iodine perovskites. We demonstrate that a key function of the organic intercalating cation is to stabilize the lead iodine octahedron through coordination with exposed lead ions and enhanced hydrogen bonding with iodine. The molecule synergistically facilitates spectral modulation, promotes charge transfer between perovskite quantum wells and reduces iodine migration under electrical bias. We realize continuously tunable emission wavelengths for iodine-based perovskite films with suppressed energy loss due to the decrease in bond energy of lead iodine in ionic perovskites as the bandgap increases. Importantly, the resultant devices show outstanding spectral stability and a half-lifetime of more than 7,600 min at an initial luminance of 100 cd m⁻².
... Pb-based perovskites are the most heavily studied light-emitting perovskites because of their suitable size, defect tolerance, and direct bandgap structure. The Pb-based perovskite has exhibited near-unity PLQY [84][85][86][87], and Pb-based PeLED has achieved the highest EQE of 30.84% [44], 26.3% [88], 18.65% [89], and 12.2% [90] for green, red, blue, and white light emissions respectively. The excellent performance indicates halide perovskite is a promising candidate for next-generation light-emitting diodes. ...
... In 2014, room-temperature EL with narrow line shapes was observed from perovskites, setting a new start for the booming research of PeLEDs [83]. During the past several years, numerous optimization strategies on device structures, material compositions, film deposition and defect passivation have been employed to enhance the performance of PeLEDs; now PeLEDs with peak EQEs over 25% have been successfully demonstrated, which are comparable to organic and quantum-dot LEDs [88,305]. ...
... But the morphology control is still important for these perovskite films, especially quasi-2D perovskite films where mixed phases occur [326]. Modulating the distribution of the different phases in quasi-2D perovskite films can control the energy transfer landscape, and thus the efficiency and emission wavelengths of the PeLEDs [88,336,337]. ...
Metal-halide perovskites have garnered considerable research attention as highly efficient light emitters in recent years due to their outstanding optoelectronic properties with remarkable tunability and excellent solution processabilities. Substantial advancements have been achieved in the development of novel halide perovskites, and the exploitations of these materials in light-emitting devices. This review comprehensively outlines recent breakthroughs in metal-halide perovskites, encompassing the rational design of perovskite materials with tunable light emission properties, the controllable growth of single crystal for a deeper understanding of their structure–property relationships, as well as the fundamental insights into the photophysics and carrier dynamics in perovskite systems. Additionally, it provides an overview of recent applications of perovskite materials in high-performance light-emitting diodes (LEDs) and lasers.
... In region 4, the target PeLEDs exhibit a steeper slope, indicating a faster carrier recombination rate, which is also favorable for device performance. Furthermore, the EL peak position of target PeLED is slightly redshift comparing with the control device, which is consistent with the PL spectra (Fig. 4f) [41]. It is noteworthy that under a bias voltage of 4 V, the KBr-modified target PeLED device exhibited a significant enhancement of the maximum electroluminescence luminance (EL max), achieving an approximately 2.5-fold increase compared to the control perovskite-based PeLED. ...
Metal halide perovskites, particularly the quasi-two-dimensional perovskite subclass, have exhibited considerable potential for next-generation electroluminescent materials for lighting and display. Nevertheless, the presence of defects within these perovskites has a substantial influence on the emission efficiency and durability of the devices. In this study, we revealed a synergistic passivation mechanism on perovskite films by using a dual-functional compound of potassium bromide. The dual functional potassium bromide on the one hand can passivate the defects of halide vacancies with bromine anions and, on the other hand, can screen the charged defects at the grain boundaries with potassium cations. This approach effectively reduces the probability of carriers quenching resulting from charged defects capture and consequently enhances the radiative recombination efficiency of perovskite thin films, leading to a significant enhancement of photoluminescence quantum yield to near-unity values (95%). Meanwhile, the potassium bromide treatment promoted the growth of homogeneous and smooth film, facilitating the charge carrier injection in the devices. Consequently, the perovskite light-emitting diodes based on this strategy achieve a maximum external quantum efficiency of ~ 21% and maximum luminance of ~ 60,000 cd m⁻². This work provides a deeper insight into the passivation mechanism of ionic compound additives in perovskite with the solution method.
Supplementary Information
The online version contains supplementary material available at 10.1007/s40820-024-01405-5.
... The fabrication process, including stages such as crystallization and post-treatment, significantly affects the formation and distribution of quasi-2D phases, which are crucial for carrier dynamics [17]. Recent studies have attempted to manipulate phase distribution and orientation within the spin-coating system by adjusting precursor solutions [18], composition [19,20], additives [21,22], and antisolvents [23]. For the fabrication of perovskite film, regardless of dimension, antisolvent engineering has been a common method to produce highly uniform and dense film with minimized non-radiative recombination [24,25]. ...
... We tried to identify the depth dependent distribution of the bulky 'A' site cation, distribution of F-PEA that might provide insight into the distribution of phases with different n-values. As the F − ion reached saturation, we utilized the F 2 − ion to provide a clearer depth profile within the perovskite layer [18,47,48]. Interestingly, the F 2 − ion intensity significantly differs at the surface under different dripping conditions. ...
Quasi-two-dimensional (quasi-2D) perovskites are increasingly explored for integration into light-emitting diodes (LEDs) as light-emissive layers. However, the quasi-2D perovskite films likely exhibit non-uniform dimensional phase distribution and irregular internal crystal structures. These characteristics are known to contribute to undesirable effects, including non-radiative recombination losses and radiative recombination in perovskites of various dimensions, impeding the realization of efficient electroluminescence and high color purity in LEDs. In this study, we present an investigation on the correlation between the dimensional distribution of quasi-2D perovskites and charge carrier behavior by modulating anti-solvent dripping during the film fabrication processes. We provide a comprehensive analysis of the impact of controlled dimensional distribution on charge injection and recombination processes associated with the performance of quasi-2D perovskite LEDs. Our work emphasizes the crucial role played by controlled dimensionality in quasi-2D perovskites in realizing efficient and stable perovskite-based LEDs.
... For perovskite LED materials (QDs or quasi-two-dimensional thin films), there exists a tradeoff between low V ex to prolong the operational stability and the demand for high V ex to increase current densities and meet practical luminance levels 1,14 . Although many studies focus on low luminance levels for stability, and generally measure stability down to T50, for real-world applications, the time taken to sustain a 10% luminance loss (T90) at an operational luminance of around 1,000 cd m −2 is more important as cell phone and computer screens require up to about 1,000 cd m −2 , and a 10% luminance loss would be considered defective. ...
... Fig. 3 | NMR spectra for surface ligand investigation. a,1 H NMR spectra for original, control and treated perovskite QDs. b, Schematic of the surface ligand variation using different ligand treatments. ...
Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs) have produced external quantum efficiencies (EQEs) of more than 25% with narrowband emission1,2, but these LEDs have limited operating lifetimes. We posit that poor long-range ordering in perovskite QD films—variations in dot size, surface ligand density and dot-to-dot stacking—inhibits carrier injection, resulting in inferior operating stability because of the large bias required to produce emission in these LEDs. Here we report a chemical treatment to improve the long-range order of perovskite QD films: the diffraction intensity from the repeating QD units increases three-fold compared with that of controls. We achieve this using a synergistic dual-ligand approach: an iodide-rich agent (aniline hydroiodide) for anion exchange and a chemically reactive agent (bromotrimethylsilane) that produces a strong acid that in situ dissolves smaller QDs to regulate size and more effectively removes less conductive ligands to enable compact, uniform and defect-free films. These films exhibit high conductivity (4 × 10⁻⁴ S m⁻¹), which is 2.5-fold higher than that of the control, and represents the highest conductivity recorded so far among perovskite QDs. The high conductivity ensures efficient charge transportation, enabling red perovskite QD-LEDs that generate a luminance of 1,000 cd m⁻² at a record-low voltage of 2.8 V. The EQE at this luminance is more than 20%. Furthermore, the stability of the operating device is 100 times better than previous red perovskite LEDs at EQEs of more than 20%.
... Introducing more sophisticated materials could significantly elevate the performance. [42][43][44] Additionally, integrating quantum dots into the perovskite layer appears to be a viable means to broaden the emission spectrum and improve color purity in PeLEDs. 45,46 Second, refining the interfaces between different PeLED layers is pivotal. ...
Light-emitting diodes utilizing halide perovskites have experienced rapid advancements in recent years, demonstrating notable external quantum efficiencies. Despite these strides, the practical implementation of such devices remains constrained. In this contribution, we are dedicated to developing perovskite light-emitting diodes with a back-contact architecture using the MAPbBr3 active layer and SnO2 and Ni/NiOx back electrodes. The quantum efficiency of the fabricated devices stands at 0.015%. The operational voltage of the light-emitting diodes is characterized by its pronounced low values, attaining a maximum luminance of 70 cd/m2 at a mere 3.2 V. These results demonstrate the considerable promise of the developed back-contact perovskite light-emitting diodes for prospective applications in advanced display technologies and light communication systems.
... [14][15][16] Quasi-2D perovskite solar cells and light emitting diodes (LEDs) have also been designed to make use of their excellent tunability by modulating the quantum well thickness as well as promote stability through careful design of bulky organic ligands. [17][18][19][20][21] Aside from optoelectronic devices, highly effective 2D perovskite field effect transistors (FETs) have also been investigated utilizing tin based 2D perovskite materials. [22][23][24] Also, memory devices integrating 2D perovskites have been demonstrated as well. ...
Two-dimensional (2D) perovskites have gained much attention lately owing to their excellent optoelectronic properties, chemical tunability, and environmental stability. Multiple methods have been devised to synthesize high quality 2D perovskite single crystals, and recent progress in fabricating its heterostructures is notable as well. In particular, with growing interest in 2D van der Waals heterostructures, 2D perovskites have become a strong candidate as a new building block for heterostructures to reveal unique physical properties across different interfaces. Until now, various heterostructure devices of 2D perovskite single crystals with other types of 2D materials such as transition metal dichalcogenides (TMDs) and graphene have been studied, which have shown intriguing results including interlayer excitons and enhanced electronic properties. Here, we introduce various synthetic approaches to realize 2D perovskite single crystals and unique characteristics of their single crystal heterostructures fabricated with precision, possessing sharp interfaces. Moreover, recent studies of semiconductor devices based on 2D perovskite single crystal heterostructures are discussed in-depth. New perspectives to further the horizon in the field of 2D perovskite heterostructures are suggested in this work including the consideration of metal–2D material van der Waals contact, application of dry transfer techniques, electric bias driven ion diffusion studies, and nanocrystal array fabrication. 2D perovskite heterostructure single crystal devices factoring in these novel perspectives will further uncover the true potential of these materials for highly efficient and stable semiconductor devices.
... [13][14][15] A major challenge in the development of quasi-2D MHP systems is the difficulty in obtaining a pure desired phase, as multiple phases are often formed during film fabrication. 16 Several efforts were attempted to regulate the multi-phase emergence via spacer engineering, 17 optimal 2D:3D MHP ratio, 13 and additive engineering. 3 Recently, the implementation of highhttps://doi.org/10.26434/chemrxiv-2023-zcvl0-v2 ...
... It has been shown that the broad phase distribution in quasi-2D MHP stems from the disproportionation of a kinetically-grown intermediate-n 2D phase. 17 Still, the understanding of early-stage formation and growth kinetics of quasi-2D MHP phases, primarily determining the phase distribution in the system before disproportionation, remains far elusive. The missing piece originates from the difficulty in capturing the features during the practical film fabrications such as spin-coating, which quickly takes place within a few seconds by solvent evaporation. ...
... This allows to comprehensively elucidate the early-stage phase growth kinetics of the quasi-2D MHP system, which cannot be deeply observed in thin-film fabrication process with advanced characteriziation techniques. 17 We investigate the phase formation kinetics and evolution of 95 different quasi-2D MHP configurations by varying the 2D:3D precursor ratios in each precursor solution. Herein, we employ a modified high-throughput automated experimental workflow specifically designed to explore the compositional space of quasi-2D MHP. ...
Quasi-two-dimensional (2D) metal halide perovskites (MHPs) are an emerging material platform for sustainable functional optoelectronics, however the uncontrollable, broad phase distribution remains a critical challenge for applications. This is because the basic principles for controlling multiple phases in quasi-2D MHPs remain poorly understood, due to the rapid crystallization kinetics during the conventional thin-film fabrication process. Herein, a high-throughput automated synthesis-characterization-analysis workflow is implemented to accelerate material exploration in formamidinium (FA)-based quasi-2D MHP compositional space, revealing the early-stage phase growth kinetics which fundamentally determines the phase distributions. We observe that the prominent n=2 2D phase restricts the growth kinetics of 3D-like phases – α-FAPbI3 MHPs where the spacers are coordinated to the surface. δ-FAPbI3 phase further inhibits the growth of 3D-like phases. It is found that thermal annealing is a critical step for proper phase growth, although it can lead to the emergence of unwanted local PbI2 crystallites. Additionally, fundamental insights into the precursor chemistry associated with spacer-solvent interaction that determines the morphologies and microstructures of quasi-2D MHP films are demonstrated. Our high-throughput study provides comprehensive insights into the fundamental principles in quasi-2D MHP phase control and enables new control of the functionalities of complex materials systems for sustainable device applications.
... We conducted the annealing process while evaporating the precursor (CsBr and PbBr 2 ), and the fabricated devices demonstrated superior performance [38]. Furthermore, the EQE of green PeLED was over 26%, which implied the great potential for the commercializatioin [39]. ...
All-inorganic perovskite materials (such as CsPbBr3) have received widespread attention because of their better stability than hybrid counterparts, but their poor film morphology and crystalline quality limit their application in perovskite light-emitting devices (PeLEDs). Some previous studies have attempted to improve the morphology and crystalline quality of perovskite films by heating the substrate, but there are still some problems such as inaccurate temperature control, excessive temperature is not conducive to flexible applications, and the mechanism of action is not clear. In this work, we used a one-step spin-coating, low-temperature in situ thermally assisted crystallization process, in which the temperature was accurately monitored using a thermocouple in the range of 23-80 °C, and explored the effect of the in situ thermally assisted crystallization temperature on the crystallization of the all-inorganic perovskite material CsPbBr3 and the performance of PeLEDs. In addition, we focused on the influence mechanism for the in situ thermally assisted crystallization process on the surface morphology and phase composition of the perovskite films and promote its possible application in inkjet printing and scratch coating methods.
... 21 In fact, the crystallization of quasi-2D MHPsa chemically complex materials systemis largely dependent on multiple physio-chemical factors. 20,[22][23][24][25][26][27] Particularly, the ratio of 2D:3D 4 compositions in the MHP precursors primarily influences the final phase constitution of the quasi-2D MHP films. 21 Notwithstanding, so far, there is no consensus or fundamental guidelines for designing an optimal 2D:3D composition ratio within a wide range of MHP compositional space exhibiting best optoelectronic performances. ...
... In this study, we specifically selected the phenethylammonium (PEA) and formamidinium (FA)-based quasi-2D MHP system, which shows promising functionalities although suffering from thermodynamic instability of functional α-FAPbI3 phase that causes phase heterogeneities. 1,13,23,26,32,33 We observe that 3D-like phases, α-FAPbI3 MHPs where the phase stability is enhanced by surface passivation of PEA cations, 10 exclusively emerge in the 2D:3D compositional space of 35-55% of FAPbI3 ratio. Note that this compositional range far deviates from the stoichiometric considerations, which is difficult to manually predict by chemical intuitions based on the handful of experiments. ...
... Various studies have explored the crystallization behavior and the resulting phase distributions in quasi-2D MHP systems, revealing that multiple parameters and factors, including solventsolute interactions, crystallization rates, ion diffusion behaviors and temperatures, can sensitively affect the resulting system. 20,[22][23][24][25][26][27] Among them, the most intuitive determinant controlling the final phase distributions of quasi-2D MHPs is the ratio of 2D:3D compositions. 21 Nevertheless, there is not a united, generalized principles on how to design the quasi-2D MHP system with an optimal 2D:3D ratio for high-performance MHP optoelectronics, even though many publications have already demonstrated excellent device performances. ...
The intriguing functionalities of emerging quasi-two-dimensional (2D) metal halide perovskites (MHPs) have led to further exploration of this material class for sustainable and scalable optoelectronic applications. However, the chemical complexities in precursors – primarily determined by the 2D:3D compositional ratio – result in uncontrolled phase heterogeneities in these materials, which compromises the optoelectronic performances. Yet, this phenomenon remains poorly understood due to the massive quasi-2D compositional space. To systematically explore the fundamental principles, herein, a high-throughput automated synthesis-characterization workflow is designed and implemented to formamidinium (FA)-based quasi-2D MHP system. It is revealed that the stable 3D-like phases, where the α-FAPbI3 surface is passivated by 2D spacer molecules, exclusively emerge at the compositional range (35-55% of FAPbI3), deviating from the stoichiometric considerations. A quantitative crystallographic study via high-throughput grazing-incidence wide-angle X-ray scattering (GIWAXS) experiments integrated with automated peak analysis function quickly reveals that the 3D-like phases are vertically aligned, facilitating vertical charge conduction that could be beneficial for optoelectronic applications. Together, this study uncovers the optimal 2D:3D compositional range for complex quasi-2D MHP systems, realizing desired optoelectronic performances and stability. The automated experimental workflow significantly accelerates materials discoveries and processing optimizations while providing fundamental insights into complex materials systems.
