Performance Of Perovskite Light-emitting Diodes Research Articles

Surface Treatment with Tailored π-Conjugated Fluorene Derivatives Significantly Enhances the Performance of Perovskite Light-Emitting Diodes.

Surface defect passivation and carrier injection regulation have emerged as effective strategies for enhancing the performance of perovskite light-emitting diodes (Pero-LEDs). It usually requires two functional molecules to realize defect passivation and carrier injection regulation separately. In other words, developing one single molecule possessing these capabilities remains challenging. Herein, we utilized π-conjugated fluorene derivatives as surface treatment materials, 9,9-Spirobi[fluorene] (SBF), 9,9-Spirobifluoren-2-yl-diphenylphosphine oxide (SPPO1), and 2,7-bis(diphenylphosphoryl)-9,9'-spirobifluorene (SPPO13), to investigate the influence of their chemical structure on device optoelectronic performance, especially for defect passivation and carrier injection regulation. Consequently, the passivation capability of double-bonded SPPO13 surpassed single-bonded SPPO1 and nonbonded SBF, which all showed excellent electron transport properties, enhancing electron injection. The maximum external quantum efficiencies (EQE) for Pero-LEDs treated with SBF, SPPO1, and SPPO13 were 8.13, 17.48, and 22.10%, respectively, exceeding that of the derivative-free device (6.55%). Notably, SPPO13-treated devices exhibited exceptional reproducibility, yielding an average EQE of 20.00 ± 1.10% based on 30 devices. This result emphasizes the potential of tailored fluorene derivatives for enhancing the device performance of Pero-LEDs.

On-Shelf and Operational Decay Dynamics of Self-Healing Quasi-Two-Dimensional Perovskite Light-Emitting Devices.

Currently, the external quantum efficiency (EQE) performance of perovskite light-emitting diodes (PeLEDs) is approaching its theoretical limit. The main drawback of PeLEDs is their stability. Ion migration in the perovskite layer is one of the main causes of the operational decomposition of PeLEDs. Here, we find that butylammonium-based quasi-two-dimensional (quasi-2D) PeLEDs show self-healing ability, revealing the existence of ion migration in the fabricated perovskite layer. Then, on the basis of the analysis of ∼170 operational decay EQE curves, patterns of on-shelf and operational decay in self-healing quasi-2D PeLEDs have been identified. The uneven distributions of resistance on the perovskite film surface are proposed to cause secondary electric fields. The electroluminescent scintillation in certain regions results in fluctuating electroluminescence of PeLEDs, further proving the existence of microcosmic steric ion movement under secondary electric fields. Our work explores the decay patterns of self-healing PeLEDs and highlights the impact of steric ion movements on the decay processes of PeLEDs.

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%.

High-performance pure red perovskite light-emitting diodes utilizing conformational transformation of ionic liquid additive

The performance of perovskite light-emitting diodes (PeLEDs) depends highly on the defect density and carrier transport properties of the perovskite layer. Some long-chain ligands are good at passivating the defects, but they hinder the charge injection into the perovskite because of their insulating nature. Notably, red PeLEDs suffer from spectral shift under bias caused by ion migration inside the mixed cation perovskite layer. This study proposes the use of silver bis(trifluoromethanesulfonyl)imide (AgTFSI) a conducting ionic liquid as a multifunctional additive to the perovskite to overcome the aforementioned problems. The TFSI anion comprises strong electronegative -CF3 and Lewis base -SO2 groups. These functional groups interact with undercoordinated Pb2+, efficiently suppressing defects and reducing nonradiative recombination in the perovskite film. AgTFSI displays two distinct conformations: cisoid and transoid. The opposing orientations of the two functional groups enable the cisoid structure to exclusively engage with the perovskite through the -SO2 groups. In contrast, the semi-linear arrangement of the transoid structure provides accessibility to both -SO2 and -CF3 groups for interaction. Owing to their conformational flexibility, the TFSI anions in AgTFSI undergo a transition from the zigzag cisoid to a more linear transoid structure when added to the perovskite, enabling efficient packing and tight binding with the Pb defects. As a result, the perovskite film shows a twofold increase in photoluminescence quantum yield and decay lifetime. Consequently, the red PeLEDs achieve a maximum external quantum efficiency of 13.52%, nearly double that of the control device. This study confirms AgTFSI's potential as an effective additive for high-performance pure red PeLEDs.

Synergetic mixed ionic liquid strategy for comprehensive defect passivation and increased carrier mobility in high-performance green perovskite light-emitting diodes

Metal halide perovskites have recently garnered significant attention owing to their potential in light-emitting diode applications. The performance of perovskite light-emitting diodes (PeLEDs) can be significantly influenced by mitigating the halide vacancy-related defects and optimizing the morphology of the perovskite layer. Achieving defect passivation in perovskites often involves the incorporation of electrically insulating long-chain ligands, which can result in the transformation of the three-dimensional perovskite structure to lower-dimensional structures. This enhances its optoelectronic properties, but reduces the interparticle charge transport, thus limiting the performance of the PeLEDs. This study demonstrates a novel approach for passivating defects by utilizing mixed ionic liquid (IL) additives, namely 1-butyl-3-methylimidazolium tetrafluoroborate (BMIMBF4) and 1-benzyl-3-methylimidazolium tetrafluoroborate (BZIMBF4). The BMIMBF4 enhances carrier mobility, whereas BZIMBF4 enhances the film morphology and improves defect passivation within the perovskite active layer. Consequently, the mixed IL strategy enables improved control over the crystal growth kinetics, alteration of crystallographic orientation, superior defect passivation, and adjustment of the energy band levels. Additionally, this IL-based approach maintains the three-dimensional structure of the perovskite, thus preserving good charge transport properties compared to organic ligands. These combined effects result in high-performance green PeLEDs with a maximum external quantum efficiency of 20.03% and a brightness of 57599.36 cd/m2.

Performance Improvement Based on Latitude Classification of Perovskite Light-Emitting Diodes

The Perovskite Light-emitting Diode (PeLED) can effectively convert light energy and electrical energy, and the study of Light-Emitting Diode (LED) is conducive to the efficient use of energy. Starting from the dimension classification of perovskite light-emitting diodes, this paper introduces the advantages of perovskite in different dimensions and the methods to improve the performance of perovskite light-emitting diodes. It is expected to realize the preparation of low-cost and high-performance perovskite light-emitting diodes. Light-emitting diodes or electroluminescent devices have many excellent properties such as high brightness, wide colour gamut, low power consumption, long life and environmental protection. They have been widely used in the field of display and lighting, and have become one of the most competitive products in the optoelectronic industry. With the development of the LED industry and the higher requirements for LED display in the new era, scientific researchers exploration of new electroluminescent materials has also been gradually strengthened. Among them, organic molecules and new low-dimensional halogenated perovskite have attracted much attention because of their many advantages. The performance of LED depends on the type of light-emitting material and device structure. It is also important to understand the light-emitting mechanism of such devices and their internal carrier transport mechanism. Studying the light-emitting mechanism and carrier transport mechanism of LEDs based on different light-emitting materials is not only of scientific significance, but also can provide a reliable theoretical basis for further improving their performance.

Charge injection engineering at organic/inorganic heterointerfaces for high-efficiency and fast-response perovskite light-emitting diodes

The development of advanced perovskite emitters has considerably improved the performance of perovskite light-emitting diodes (LEDs). However, the further development of perovskite LEDs requires ideal device electrical properties, which strongly depend on its interfaces. In perovskite LEDs with conventional p-i-n structures, hole injection is generally less efficient than electron injection, causing charge imbalance. Furthermore, the popular hole injection structure of NiOx/poly(9-vinylcarbazole) suffers from several issues, such as weak interfacial adhesion, high interfacial trap density and mismatched energy levels. In this work, we insert a self-assembled monolayer of [2-(9H-carbazol-9-yl)ethyl]phosphonic acid between the NiOx and poly(9-vinylcarbazole) layers to overcome these challenges at the organic/inorganic heterointerfaces by establishing a robust interface, passivating interfacial trap states and aligning the energy levels. We successfully demonstrate blue (emission at 493 nm) and green (emission at 515 nm) devices with external quantum efficiencies of 14.5% and 26.0%, respectively. More importantly, the self-assembled monolayer also gives rise to devices with much faster response speeds by reducing interfacial capacitance and resistance. Our results pave the way for developing more efficient and brighter perovskite LEDs with quick response, widening their potential application scope.

Improved performance of perovskite light-emitting diodes via bifacial modification

Improved performance of perovskite light-emitting diodes via bifacial modification

Bifunctional Molecule for Highly Efficient Green Perovskite Light‐Emitting Diodes

AbstractQuasi‐2D perovskites have emerged as a promising material for the fabrication of perovskite light‐emitting diodes (PeLEDs) owing to their excellent photoelectronic properties. The realization of efficient PeLEDs relies critically on the effective energy transfer and radiation recombination in quasi‐2D perovskites. However, the performance of PeLEDs is hindered by the disordered distribution of n‐values and a large number of surface defects in quasi‐2D perovskites, which significantly impacts their practical application and further development. Herein, a passivation strategy utilizing the bifunctional additive sodium hexafluorophosphate (NaPF6) is proposed. The introduction of PF6− anions substantially inhibits the formation of low‐n phases, which can accelerate the effective energy transfer within the quasi‐2D perovskites. Furthermore, the lone electron pairs in PF6− anions can pair with the uncoordinated Pb2+ cations of perovskites to passivate defects. As a result, the champion green PeLED modified with NaPF6 exhibits a remarkable external quantum efficiency (EQE) of 20.13% and a current efficiency (CE) of 67.54 cd A−1, which represents a significant improvement compared with the 11.26% EQE and the CE of 37.38 cd A−1 of the control sample.

Enhanced Performance of Perovskite Light-Emitting Diodes via Phenylmethylamine Passivation

Organic-inorganic perovskite materials are widely used in the preparation of light-emitting diodes due to their low raw material cost, solution preparation, high color purity, high fluorescence quantum yield, continuously tunable spectrum, and excellent charge transport properties. It has become a research hotspot in the field of optoelectronics today. At present, the nonradiative recombination and fluorescence quenching occurring at the interface between the device transport layer and the light-emitting layer are still important factors limiting the performance of perovskite light-emitting diodes (PeLEDs). In this work, based on CH3NH3PbBr3 perovskite, the effects of parameters such as precursor solution, anti-solvent chlorobenzene (CB), and small amine molecule phenylmethylamine (PMA) on the performance of perovskite films and devices were investigated. The research results show that adding an appropriate amount of PMA can reduce the grain size of perovskite, improve the coverage of the film, enhance the crystallinity of the film, and increase the fluorescence intensity of the perovskite film. When the PMA content is 0.050 vol.%, the maximum luminance of PeLEDs is 2098 cd/m2 and the maximum current efficiency is 1.592 cd/A, which is greatly improved by 30% and 64.8% compared with the reference device without PMA doping. These results suggest that an appropriate amount of PMA can effectively passivate the defects in perovskite films, and inhibit the non-radiative recombination caused by the traps, thereby improving the optoelectronic performance of the device.

Bio-Inspired Pangolin Design for Self-Healable Flexible Perovskite Light-Emitting Diodes.

Despite tremendous developments in the luminescene performance of perovskite light-emitting diodes (PeLEDs), the brittle nature of perovskite crystals and their poor crystallinity on flexible substrates inevitably lead to inferior performance. Inspired by pangolins' combination of rigid scales and soft flesh, we propose a bionic structure design for self-healing flexible PeLEDs by employing a polymer-assisted crystal regulation method with a soft elastomer of diphenylmethane diisocyanate polyurethane (MDI-PU). The crystallinity and flexural strain resistance of such perovskite films on plastics with silver-nanowire-based flexible transparent electrodes are highly enhanced. The detrimental cracks induced during repeated deformation can be effectively self-healed under heat treatment via intramolecular/intermolecular hydrogen bonds with MDI-PU. Upon collective optimization of the perovskite films and device architecture, the blue-emitting flexible PeLEDs can achieve a record external quantum efficiency of 13.5% and high resistance to flexural strain, which retain 87.8 and 80.7% of their initial efficiency after repeated bending and twisting operations of 2000 cycles, respectively.

Enhancing the performance of perovskite light-emitting diodes via the insertion of NaCl

All-inorganic perovskite light-emitting diodes (PeLEDs) have the advantage of narrow band emission, superior thermal stability and high chemical stability. However, CsPbBr3 PeLEDs usually suffered from huge current leakage and low device efficiency due to the poor surface coverage of CsPbBr3 on the hole transport layer (HTL). Thus, improving the morphology of CsPbBr3 layer is an effective strategy to enhance the performance of PeLEDs. In this report, NaCl was introduced on the surface of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)(PEDOT:PSS) to assist the crystal growth of CsPbBr3. Experimental results show that CsPbBr3 film with less pinholes and lower trap density was obtained, resulting in an enhancement of photoluminescent (PL) intensity. The luminous current efficiency (LE) of PeLED increased from 7.4 cd/A to 12.8 cd/A. The work mechanism of the introduction of NaCl was discussed. This work provides an effective and convenient method to improve the efficiency of all-inorganic PeLEDs.

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.

Significant electroluminescence efficiency and stability enhancements in perovskite light-emitting diodes with double additives

Perovskite light-emitting diodes (PeLEDs) as the next-generation display have been attracting wide attention due to high color purity, high photoluminescence quantum-yields (PLQYs), and easily tunable bandgap. Perovskite film quality has been being a fatal factor influencing electroluminescence (EL) performance of PeLEDs. The big pinholes and high roughness in the pristine CsPbBr3 perovskite film cause severely leakage current. In addition, the low PLQY indicates that the perovskite film retains poor radiative recombination. These may lead to a limited EL performance for PeLEDs. Therefore, in this work, to obtain an perovskite film with full coverage surface and desirable optical property, the long ligand 2-phenylethanamine bromide (PEABr) was introduced into CsPbBr3 perovskite solution firstly. After the introduction of PEABr, the photoluminescence (PL) intensity and perovskite morphology quality have been improved. Meanwhile, the exiton quantum confinement is enhanced by the layerd structure in the PEA2Csn-1PbnBr3n+1 perovskite film. Secondly, an organic molecule, named benzyltriphenylphosphonium chloride (BTPPC), was further introduced into the perovskite precursor solution to enhance crystallization process to obtain a better perovskite film with less pinholes and smaller grains. Finally, the PeLEDs with two additives achieved the best external quantum efficiency (EQE) of 11.9%, which is 45.7-fold to that of the pristine device. And the stability of the PeLEDs can be improved from 240 s to 2079 s under an initial luminance of 1000. cd/m2.

Enhancing the Performance of Perovskite Light-Emitting Diodes by Humidity Treatment.

While humidity treatment has been employed for enhancing the performance of perovskite solar cells and light-emitting diodes (LEDs), only very limited success has been achieved in quasi-two-dimensional (2D) perovskite LEDs (PeLEDs). Here, for the first time, we demonstrate more than one order of magnitude enhancement of the external quantum efficiency (EQE) and electroluminescence (EL) intensity in blue CsPb(Cl/Br)3 PeLEDs with an organic cation of 2,2-(ethylenedioxy)bis(ethylammonium) (EDBE). Upon humidity treatment, the crystallinity of the three-dimensional (3D) perovskite phase in the EDBE-based perovskite is improved, contributing to an enhancement of photoluminescence quantum yield (PLQY). This work suggests that elaborately modulating the molecular structure of large cations under humidity treatment can serve as an effective strategy to improve the performance of quasi-2D PeLEDs.

The Rational Control of Precursor Concentration in Perovskite Light-Emitting Diodes

Perovskite light-emitting diodes (PeLEDs) have attracted tremendous attention due to their ideal optoelectronic properties, such as high color purity, high fluorescence quantum yield, and tunable light color. The perovskite layer plays a decisive role in the performance of PeLEDs and the solvent engineering of the perovskite layer is the key technological breakthrough in preparing high quality films. In this study, we have proposed the strategy of adding different amounts of solvents to the perovskite precursor solution to optimize the morphology of perovskite films and device performance. As a result, with the decreasing concentration of perovskite precursor solution, the perovskite film morphology is smoother and more favorable for carrier injection and combing, which induces an enhanced external quantum efficiency. The maximum luminance of PeLEDs was increased from 1667 cd/m2 to 9857 cd/m2 and the maximum current efficiency was increased from 6.7 cd/A to 19 cd/A. This work provides a trend to achieve improved film morphology and device performance for perovskite optoelectronic devices.

Exploiting a Multiphase Pure Formamidinium Lead Perovskite for Efficient Green-Light-Emitting Diodes.

Formamidinium (FA)-based perovskites have demonstrated excellent advances in optoelectronics recently, but in terms of perovskite compounds, the optimal condition of their composition optimization remains controversial. Herein, we boosted the performance of perovskite light-emitting diodes (PeLEDs) in both efficiency and stability through composition and phase engineering. The low-dimensional FA2PbBr4 particles emerged and mixed with the FAPbBr3 composites when the FABr content is excessive. By regulating the phase composition in multiphase FAPbBr3 perovskites, the maximum external quantum efficiency (EQEmax) of optimal PeLEDs (5.14%) is 2.7-fold higher than that of pure FAPbBr3-based PeLEDs (1.90%), and device stability is improved. Further optimizing the film quality and emission efficiency with Rb+ ions, the EQEmax of PeLEDs can be increased to 6.01%, with a half-lifetime of about 185 s under the high current density. This strategy of phase composition optimization in FA-based perovskites provides an effective way to process high-efficiency and stable PeLEDs.

Position Effects of Metal Nanoparticles on the Performance of Perovskite Light-Emitting Diodes.

Metal nanoparticles have been widely used for improving the efficiencies of many optoelectronic devices. Herein, position effects of gold nanoparticles (Au NPs) on the performance of perovskite light-emitting diodes (PeLEDs) are investigated. Amphiphilic Au NPs are synthesized so that they can be incorporated into different layers of the PeLEDs to enhance device efficiencies. The photoluminescent (PL) studies indicate apparent position effects; the strongest PL intensity occurs when the NPs are directly blended with the light-emitting perovskite layer. In contrast, the PeLEDs exhibit the highest luminance efficiency while the Au NPs are placed in the hole-transporting layer. The direct blending of the NPs in the perovskite layer might affect the electrical properties, resulting in inferior device performance. The results reported herein can help to understand the enhancing mechanism of the PeLEDs and may also lead to even better efficiencies in the near future.

Recent Progress on Patterning Strategies for Perovskite Light‐Emitting Diodes toward a Full‐Color Display Prototype

Perovskite light‐emitting diodes (PeLEDs) have attracted both academic and industrial interest because of their high efficiency, wide color gamut as well as low material and fabrication costs. However, most state‐of‐the‐art PeLEDs are still fabricated with commonly used spin‐coating methods, which are undesirable for large‐scale commercial production. Achieving highly emissive perovskite microarrays at high spatial resolution with quick and large‐scale growth is one of the critical steps to integrate state‐of‐the‐art PeLEDs into full‐color display panels. Here, the fabrication methods and crystallization processes of perovskite materials are first discussed because they are strongly relevant to the patterning process and the quality of the perovskite pixels. Then, the current strategies to realize perovskite patterns that can be likely integrated into display panels, through mask‐free or mask‐assisted methods, are explored. Self‐emitting and down‐conversion PeLED devices with a patterned perovskite matrix as the emissive layer are also reviewed. Finally, an outlook is provided on how to further improve the optical and electrical properties of the perovskite patterns and the performance of PeLEDs as well as to develop eco‐friendly devices to accelerate the potential commercialization progress of this young technique.

A donor-acceptor ligand boosting the performance of FA0.8Cs0.2PbBr3 nanocrystal light-emitting diodes.

A donor-acceptor ligand, 3-amino-2-bromo-6-methoxypyridine (ABMeoPy), was introduced to passivate FA0.8Cs0.2PbBr3 nanocrystals (NCs) by a post-processing method. The donor-acceptor interaction can greatly enhance the coordination bond of pyridine-Pb2+, and improve FA0.8Cs0.2PbBr3 NC performance with 95.99% photoluminescence quantum yield (PLQY), 6-month stability in solution, and 26% trap density decrease. In the light of ABMeoPy passivation of FA0.8Cs0.2PbBr3 NCs, the maximum luminance, the maximum current efficiency, and EQE of light-emitting diodes (LEDs) increased 69%, 110%, and 111%, respectively. The strategy of using D-A molecules to passivate perovskite NCs is quite simple and effective, which can be widely promoted in perovskite-based LEDs or solar cells.