Stable Perovskite Light-emitting Diodes Research Articles

Phase dimensions resolving of efficient and stable perovskite light-emitting diodes at high brightness

Phase dimensions resolving of efficient and stable perovskite light-emitting diodes at high brightness

Metal Halide Perovskites: Promising Materials for Light-Emitting Diodes

Metal halide perovskites have shown excellent optoelectronic properties, including high photoluminescence quantum yield, tunable emission wavelengths, narrow full-width at half-maximums and a low-cost, solution-processed fabrication, which make it exhibit great potential as emission-layer materials of light-emitting diodes. With the joint efforts of researchers from different disciplines, there has been a significant progress in the improvement in the external quantum efficiency (EQE) and stability of perovskite light-emitting diodes (PeLEDs) in recent years, especially in green PeLEDs with EQEs over 30%. However, their operational stability lags behind other commercial organic and chalcogenide quantum dot emitters, limiting their practical application. In this review, we first introduce the basic device structure of PeLEDs, as well as the factors influencing the EQE and stability of PeLEDs. Secondly, the development of lead-based and lead-free PeLEDs are summarized systematically. Thirdly, challenges of PeLEDs are discussed in detail, including low the EQE of blue PeLEDs, poor device stability and EQE roll-off. Finally, some suggestions and perspectives for future research directions for PeLEDs are proposed.

Low-dimensional nanomaterial-enabled efficient and stable perovskite light-emitting diodes: recent progress and challenges

This article reviews the research progress and challenges of multi-functional low-dimensional nanomaterials in advanced perovskite light-emitting diodes.

Advances and future perspectives in polycrystalline halide perovskite light-emitting diodes

Metal halide perovskites (MHPs) have emerged as a highly promising candidate for next-generation light-emitting materials due to their exceptional optoelectronic properties. These properties include superior color purity, high photoluminescence quantum efficiency (PLQY), and the facile tunability of bandgap through compositional and dimensional control. Particularly, polycrystalline perovskites have been introduced as the first perovskite light-emitting diodes (PeLEDs) with superior charge mobility. However, the development of efficient and stable PeLEDs, crucial for commercialization, has proven to be a significant challenge due to the low exciton binding energy (E b) and inherent defects. Nevertheless, recent achievements have demonstrated polycrystalline PeLEDs with an external quantum efficiency (EQE) surpassing 28% and a half-lifetime (T 50) exceeding 30,000 h. In this review, we present the progress of polycrystalline PeLEDs with improved efficiency (PLQY, EQE) and stability by focusing on grain size regulation, defect passivation, and dimensional control. This review offers promising strategies for realizing polycrystalline perovskite material as a light emitter, highlights limitations and provides future perspectives for advancing PeLEDs.

Iodotrimethylsilane as a Reactive Ligand for Surface Etching and Passivation of Perovskite Nanocrystals toward Efficient Pure-red to Deep-red LEDs.

Resurfacing perovskite nanocrystals (NCs) with tight-binding and conductive ligands to resolve the dynamic ligands - surface interaction is the fundamental issue for their applications in perovskite light-emitting diodes (PeLEDs). Although various types of surface ligands have been proposed, these ligands either exhibit weak Lewis acid/based interactions or need high polar solvents for dissolution and passivation, resulting in a compromise in the efficiency and stability of PeLEDs. Herein, we report a chemically reactive agent (Iodotrimethylsilane, TMIS) to address the trade-off among conductivity, solubility and passivation using all-inorganic CsPbI3 NCs. The liquid TMIS ensures good solubility in non-polar solvents and reacts with oleate ligands and produces in-situ HI for surface etching and passivation, enabling strong-binding ligands on the NCs surface. We report, as a result, red PeLEDs with an external quantum efficiency (EQE) of ~23%, which is 11.2-fold higher than the control, and is among the highest CsPbI3 PeLEDs. We further demonstrate the university of this ligand strategy in the pure bromide system (CsPbBr3), and report EQE of ~20% at 640, 652, and 664 nm. This represents the first demonstration of ligand strategy that applies to different systems and works effectively in red PeLEDs spanning emission from pure-red to deep-red.

Iodotrimethylsilane as a Reactive Ligand for Surface Etching and Passivation of Perovskite Nanocrystals toward Efficient Pure‐red to Deep‐red LEDs

AbstractResurfacing perovskite nanocrystals (NCs) with tight‐binding and conductive ligands to resolve the dynamic ligands—surface interaction is the fundamental issue for their applications in perovskite light‐emitting diodes (PeLEDs). Although various types of surface ligands have been proposed, these ligands either exhibit weak Lewis acid/base interactions or need high polar solvents for dissolution and passivation, resulting in a compromise in the efficiency and stability of PeLEDs. Herein, we report a chemically reactive agent (Iodotrimethylsilane, TMIS) to address the trade‐off among conductivity, solubility and passivation using all‐inorganic CsPbI3 NCs. The liquid TMIS ensures good solubility in non‐polar solvents and reacts with oleate ligands and produces in situ HI for surface etching and passivation, enabling strong‐binding ligands on the NCs surface. We report, as a result, red PeLEDs with an external quantum efficiency (EQE) of ≈23 %, which is 11.2‐fold higher than the control, and is among the highest CsPbI3 PeLEDs. We further demonstrate the universality of this ligand strategy in the pure bromide system (CsPbBr3), and report EQE of ≈20 % at 640, 652, and 664 nm. This represents the first demonstration of a chemically reactive ligand strategy that applies to different systems and works effectively in red PeLEDs spanning emission from pure‐red to deep‐red.

Bright and stable perovskite light-emitting diodes in the near-infrared range.

Perovskite light-emitting diodes (LEDs) have attracted broad attention due to their rapidly increasing external quantum efficiencies (EQEs)1-15. However, most high EQEs of perovskite LEDs are reported at low current densities (<1 mA cm-2) and low brightness. Decrease in efficiency and rapid degradation at high brightness inhibit their practical applications. Here, we demonstrate perovskite LEDs with exceptional performance at high brightness, achieved by the introduction of a multifunctional molecule that simultaneously removes non-radiative regions in the perovskite films and suppresses luminescence quenching of perovskites at the interface with charge-transport layers. The resulting LEDs emit near-infrared light at 800 nm, show a peak EQE of 23.8% at 33 mA cm-2 and retain EQEs more than 10% at high current densities of up to 1,000 mA cm-2. In pulsed operation, they retain EQE of 16% at an ultrahigh current density of 4,000 mA cm-2, along with a high radiance of more than 3,200 W s-1 m-2. Notably, an operational half-lifetime of 32 h at an initial radiance of 107 W s-1 m-2 has been achieved, representing the best stability for perovskite LEDs having EQEs exceeding 20% at high brightness levels. The demonstration of efficient and stable perovskite LEDs at high brightness is an important step towards commercialization and opens up new opportunities beyond conventional LED technologies, such as perovskite electrically pumped lasers.

A Mixed Organic-Inorganic Interlayer With Tunable Electrical Properties Enabling Stable and Efficient Perovskite Light-Emitting Diodes

The operational stability of perovskite light-emitting diodes (PeLEDs) is subjected to undesired Joule heating induced by the charge imbalance and the current leakage. The hole injection efficiency is inferior to that of electrons in the electron-dominated PeLEDs, owing to the low hole mobility of hole transport materials and a relatively large hole injection barrier. Herein, we inserted a mixed interlayer of 4,7-diphenyl-1,10-phenanthroline and cesium carbonate (Bphen:Cs2CO3) (~10 nm) between the electron transport layer (ETL) TPBi and the metal cathode to improve the charge imbalance by optimizing the electron injection and suppressing the current leakage. Compared to TPBi, the Bphen interlayer builds a larger electron injection barrier from the cathode to perovskite layer owing to its shallower lowest unoccupied molecular orbital (LUMO), leading to inefficient electron injection. The Cs2CO3, an n-type dopant, was co-evaporated with Bphen to increase the conductivity and thus balance the electron and hole transport. The resultant quasi-2D PeLED achieves an external quantum efficiency of 17.62% and an operational lifetime of over 1900 min at an initial luminance of 100 cd <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$\text{m}^{-{2}}$ </tex-math></inline-formula> .

Manipulating Crystallization Dynamics for Efficient and Spectrally Stable Blue Perovskite Light‐Emitting Diodes

AbstractReduced‐dimensional perovskite light‐emitting diodes (PeLEDs) have shown great potential in solution‐processed high‐definition displays. However, the inferior electroluminescent (EL) performance of blue PeLEDs has become a huge challenge for their commercialization. The inefficient domain control [number of PbX6− layers (n)] and deleterious phase segregation make the blue PeLEDs suffer from low EL efficiency and poor spectral stability. Here, a rational strategy for perovskite crystallization control by adjusting the precursor concentration is proposed for improving phase distribution and suppressing ion migration in reduced‐dimensional mixed‐halide blue perovskite films. Based on this method, efficient sky‐blue PeLEDs exhibit a maximum external quantum efficiency (EQE) of 8.5% with stable EL spectra at 482 nm. Additionally, spectrally stable pure‐blue PeLEDs at 474 and 468 nm are further obtained with maximum EQEs of 4.0% and 2.4%, respectively. These findings may provide an alternative scheme for manipulating perovskite crystallization dynamics toward efficient and stable PeLEDs.

Degradation mechanisms of perovskite light-emitting diodes under electrical bias

Abstract Metal-halide perovskite light-emitting diodes (PeLEDs) are considered as new-generation highly efficient luminescent materials for application in displays and solid-state lighting. Since the first successful demonstration of PeLEDs in 2014, the research on the development of efficient PeLEDs has progressed significantly. Although the device efficiency has significantly improved over a short period of time, their overall performance has not yet reached the levels of mature technologies for practical applications. Various degradation processes are the major impediment to improving the performance and stability of PeLED devices. In this review, we discuss various analysis techniques that are necessary to gain insights into the effects of various degradation mechanisms on the performance and stability of PeLEDs. Based on the causes and effects of external and internal factors, the degradation processes and associated mechanisms are examined in terms of critical physical and chemical parameters. Further, according to the progress of the current research, the challenges faced in studying degradation mechanisms are also elucidated. Given the universality of the degradation behavior, an in-depth understanding of the device degradation may promote the development of optimization strategies and further improve the performance and stability of PeLEDs.

Ultra-bright, efficient and stable perovskite light-emitting diodes.

Metal halide perovskites are attracting a lot of attention as next-generation light-emitting materials owing to their excellent emission properties, with narrow band emission1-4. However, perovskite light-emitting diodes (PeLEDs), irrespective of their material type (polycrystals or nanocrystals), have not realized high luminance, high efficiency and long lifetime simultaneously, as they are influenced by intrinsic limitations related to the trade-off of properties between charge transport and confinement in each type of perovskite material5-8. Here, we report an ultra-bright, efficient and stable PeLED made of core/shell perovskite nanocrystals with a size of approximately 10 nm, obtained using a simple in situ reaction of benzylphosphonic acid (BPA) additive with three-dimensional (3D) polycrystalline perovskite films, without separate synthesis processes. During the reaction, large 3D crystals are split into nanocrystals and the BPA surrounds the nanocrystals, achieving strong carrier confinement. The BPA shell passivates the undercoordinated lead atoms by forming covalent bonds, and thereby greatly reduces the trap density while maintaining good charge-transport properties for the 3D perovskites. We demonstrate simultaneously efficient, bright and stable PeLEDs that have a maximum brightness of approximately 470,000 cd m-2, maximum external quantum efficiency of 28.9% (average = 25.2 ± 1.6% over 40 devices), maximum current efficiency of 151 cd A-1 and half-lifetime of 520 h at 1,000 cd m-2 (estimated half-lifetime >30,000 h at 100 cd m-2). Our work sheds light on the possibility that PeLEDs can be commercialized in the future display industry.

Impacts of the Lattice Strain on Perovskite Light‐Emitting Diodes

AbstractThe development of perovskite light‐emitting diodes (PeLEDs) with both high efficiency and excellent stability remains challenging. Herein, a strong correlation between the lattice strain in perovskite films and the stability of resulting PeLEDs is revealed. Based on high‐efficiency PeLEDs, the device lifetime is optimized by rationally tailoring the lattice strain in perovskite films. A PeLED with a high peak external quantum efficiency of 18.2% and a long lifetime of 151 h (T70, under a current density of 20 mA cm−2) is realized with a minimized lattice strain in the perovskite film. In addition, an increase in the lattice strain is found during the long‐time device stability test, indicating that the degradation of the local perovskite lattice structure could be one of the degradation mechanisms for long‐term stable PeLEDs.

Strategies to Improve the Stability of Perovskite Light-Emitting Diodes: Progress and Perspective.

Perovskite light-emitting diodes (PeLEDs) featuring excellent electroluminescent (EL) characteristics and facile production have been emerging as promising candidates for next-generation high-definition displays. In recent years, tremendous advances have been achieved in the EL efficiency of PeLEDs. However, their poor operational stability impedes practical applications. Particularly, the severe spectral instability of pure-blue and pure-red PeLEDs lags far behind the requirements of commercial displays. In this Perspective, the critical factors related to device degradation are first summarized, including perovskite crystal defects, unbalanced charge injection, Auger recombination, and Joule heating. Then, the recent progress in improving the operational and spectral stabilities is reviewed in categories. Considering the present achievements, we provide potential research directions for further development of stable PeLEDs.

Deep‐Red Perovskite Light‐Emitting Diodes with External Quantum Efficiency Exceeding 21% Enabled by Ligand‐Modulated Dimensionality Control

AbstractQuasi‐2D perovskites show great promise for light‐emitting diodes owing to suppressed non‐radiative losses enabled by the energy funneling/cascading nanostructures. However, for red emission quasi‐2D perovskites, these ideal energy landscapes for efficient perovskite light‐emitting diodes (PeLEDs) can rarely be achieved due to detrimental aggregation of the low‐dimensional ligands in perovskite precursors, leading to poor device efficiency and stability. Here, a ligand‐modulated dimensionality control strategy is explored to achieve uniform phase distribution and reduce defect density for efficient light emission. In contrast to the model phenethylammonium iodide 2D ligand, the formation of small‐n phases can be inhibited by a structurally similar phenoxyethylammonium iodide ligand owing to the weakened aromatic stacking between ligands. Besides, the oxygen atoms can interact with the uncoordinated Pb2+ ions and promote the NI coordination in the perovskites, which greatly reduces the non‐radiative recombination defects in the ionic lattice. With this simple and effective approach, deep‐red quasi‐2D PeLEDs with record‐high external quantum efficiency of 21.6% and decent operational stability are achieved without the need for additional additives. These results highlight the potential of ligand‐modulated dimensionality control to achieve highly efficient and stable PeLEDs with a facile fabrication process.

Metal Halide Perovskites for Red‐Emission Light‐Emitting Diodes

Metal halide perovskites (MHPs) exhibit remarkable optoelectronic properties, thus attracting widespread attention. Over the last several years, the external quantum efficiencies of perovskite light‐emitting diodes (PeLEDs) have exceeded 20%. Despite great progresses have been made, it remains challenging to realize high performance and stable PeLEDs. Especially, red‐emission PeLEDs still cannot meet the requirement of Rec. 2100 standard. Understanding the relationship between perovskite structure and their photophysical properties will greatly facilitate the development of PeLEDs. In this review, the structural and photophysical properties of MHPs are summarized, emphasizing three archetypes (CsPbI3, FAPbI3, and MAPbI3) of perovskites for red emission. Based on the fundamental characteristics, the recently emerged optical property modulation for obtaining high‐quality red‐emission perovskite films is outlined. Then, the approaches to optimizing electronics property and extending the operational lifetime of red‐emission PeLEDs are summarized. Finally, an outlook on the future challenges and potential directions toward red‐emission PeLEDs is represented.

Trade-off between the Performance and Stability of Perovskite Light-Emitting Diodes with Excess Halides.

Incorporation of excess bulky organoammonium halides as additives is an efficient way to enhance the performance of perovskite light-emitting diodes (PeLEDs). The excess organoammonium halides can decrease the grain size and minimize the trap density to enhance radiative recombination. In this work, we reveal that the halides in excess additives also play a critical role in the operation stability of PeLEDs. With an increasing excess halide ratio, perovskite films gradually change from being rich in halide vacancies (VI) to being rich in halide interstitials (Ii), both of which can promote halide migration and reduce the operation stability. By using mixed 4-fluorophenylmethylammonium iodide and 4-fluorophenylmethylamine as additives, the excess halide ratio can be controlled and both VI and Ii can be minimized. Therefore, the operation stability of methylammonium lead iodide-based PeLEDs is enhanced significantly from 40 to 520 min. This work emphasizes the importance of controlling excess halide concentrations in terms of device performance and operation stability.

A Multifunctional Ionic Liquid Additive Enabling Stable and Efficient Perovskite Light-Emitting Diodes.

The electroluminescence performance and long-term stability of perovskite light-emitting diodes (PeLEDs) are greatly affected by the film quality of perovskite emitting layer. Herein, the authors employ an ionic liquid, 1-butyl-3-methylimidazolium trifluoromethanesulfonate ([BMIm]OTf), to manipulate the growth of quasi-2D perovskite films by providing heterogeneous nucleation sites. The [BMIm]OTf molecules simultaneously realize uniform perovskite films by reducing the contact angles of precursor solution on the hole transport layer (HTL), and eliminate defect states through bonding [BMIm]+ cations to negatively-charged uncoordinated Br and OTf- anions to uncoordinated Pb2+ defects that effectively suppresses the defect states assisted nonradiative recombination in perovskite films. As a result, the efficiency and the operational lifetime of the resultant PeLED are enhanced by more than twofold and threefold, respectively, achieving a maximum external quantum efficiency of 17.6% and an operational lifetime of over 500min at an initial brightness of 100cd m-2 .

High-Performance Blue Perovskite Light-Emitting Diodes Enabled by a Sacrificial Agent Maleic Anhydride

In addition to eliminating the defects to suppress electric-field-induced ion migration, developing metal halide perovskites (MHPs) with good environmental stability against light, oxygen, moisture, and heat is highly desirable for the stability of perovskite light-emitting diodes (PeLEDs). As for the environmental issues, moisture should be considered as the primary critical degradation pathway. Herein, we introduce a facile approach to improving both the efficiency and the stability of blue PeLEDs via a sacrificial agent maleic anhydride (MAH). It is able to passivate the defects as well as absorb water that infiltrates into the perovskite to protect the perovskite against moisture. Furthermore, its resulting hydrolysis product maleic acid (MA) can also act as a passivation agent for the perovskite via the interaction between the carboxyl groups and uncoordinated lead ions. In addition, the incorporation of MAH into the perovskite film yields dense and smooth morphology. As a result, the blue PeLED involving MAH shows increased maximum external quantum efficiency (EQEmax) from 4.0 to ca. 5.2%, and simultaneously improved operational stability, in contrast with the pristine PeLED.

Conductive Phosphine Oxide Passivator Enables Efficient Perovskite Light-Emitting Diodes.

Recently, surface passivation has been proved to be an essential approach for obtaining efficient and stable perovskite light-emitting diodes (Pero-LEDs). Phosphine oxides performed well as passivators in many reports. However, the most commonly used phosphine oxides are insulators, which may inhibit carrier transport between the perovskite emitter and charge-transporter layers, limiting the corresponding device performance. Here, 2,7-bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13), a conductive molecule with two phosphine oxide functional groups, is introduced to modify the perovskite emitting layer. The bifunctional SPPO13 can passivate the nonradiative defects of perovskite and promote electron injection at the interface of perovskite emitter and electron-transporter layers. As a result, the corresponding Pero-LEDs obtain a maximum external quantum efficiency (EQE) of 22.3%. In addition, the Pero-LEDs achieve extremely high brightness with a maximum of around 190 000 cd/m2.

ZnO-Based Electron-Transporting Layers for Perovskite Light-Emitting Diodes: Controlling the Interfacial Reactions.

Perovskite light-emitting diodes (PeLEDs) provide new opportunities for cost-effective and large-area electroluminescent devices. It is of interest to use ZnO-based electron-transport layers (ETLs), which demonstrate superior performance in other solution-processed LEDs, in PeLEDs. However, the notorious deprotonation reaction between ZnO and perovskite casts doubt on the long-term stability of PeLEDs with ZnO-based ETLs. This Perspective presents an overview of the chemical reactions that may occur at the interfaces between perovskite and ZnO-based ETLs. We highlight that other interfacial reactions during the fabrication of PeLEDs, including the reactions between ZnO and the intermediate phase during perovskite crystallization and the amidation reactions catalyzed by ZnO, demonstrate critical utilities in the fabrication of high-efficiency and stable PeLEDs. Considering these recent advances, we propose future directions and prospects to design and control the interfacial reactions, aiming to fully exploit the potential of ZnO-based ETLs for realizing high-performance PeLEDs.