Perovskite Light-emitting Diodes Research Articles

Reduced-Toxicity and Highly Luminescent Germanium-Lead Perovskites Enabled by Strain Reduction for Light-Emitting Diodes.

Germanium-lead (Ge-Pb) perovskites provide a promising solution for perovskite optoelectronic devices with reduced toxicity. However, Ge-Pb perovskite light-emitting diodes (PeLEDs) with >30 mol % Ge showed low emission efficiencies [Yang, D.; Zhang, G.; Lai, R.; Cheng, Y.; Lian, Y.; Rao, M.; Huo, D.; Lan, D.; Zhao, B.; Di, D. Germanium-Lead Perovskite Light-Emitting Diodes. Nat. Commun. 2021, 12 (1), 4295]. Here, we apply strain engineering to effectively improve the light emission efficiency and stability of Ge-Pb perovskite films and PeLEDs with 30 and 60 mol % Ge, through A-site modulation. The maximum external quantum efficiencies of the Ge-Pb PeLEDs with 30 and 60 mol % Ge are 8.5% and 3.0% at 3.32 mA cm-2 (∼922 cd m-2) and 0.53 mA cm-2 (∼60 cd m-2), respectively. Time-resolved transient absorption spectroscopy analysis of Ge-Pb perovskite films on different hole-transport layers shows that incorporating 30 mol % Ge into the perovskite with mixed A-site cations can effectively suppress trap-assisted recombination. Further analysis of their current density-voltage (J-V) curves reveals the efficiency loss mechanisms of Ge-Pb PeLEDs with high Ge fractions, indicating the possibility of further improvements.

Efficient and stable hybrid perovskite-organic light-emitting diodes with external quantum efficiency exceeding 40 per cent

Light-emitting diodes (LEDs) based on perovskite semiconductor materials with tunable emission wavelength in visible light range as well as narrow linewidth are potential competitors among current light-emitting display technologies, but still suffer from severe instability driven by electric field. Here, we develop a stable, efficient and high-color purity hybrid LED with a tandem structure by combining the perovskite LED and the commercial organic LED technologies to accelerate the practical application of perovskites. Perovskite LED and organic LED with close photoluminescence peak are selected to maximize photon emission without photon reabsorption and to achieve the narrowed emission spectra. By designing an efficient interconnecting layer with p-type interface doping that provides good opto-electric coupling and reduces Joule heating, the resulting green emitting hybrid LED shows a narrow linewidth of around 30 nm, a peak luminance of over 176,000 cd m−2, a maximum external quantum efficiency of over 40%, and an operational half-lifetime of over 42,000 h.

Fabrication of red-emitting perovskite LEDs by stabilizing their octahedral structure.

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.

Ligands Optimization Governed by Solubility Principles for Pure Blue Emission in Mixed-Halide Perovskite LEDs

Ligands Optimization Governed by Solubility Principles for Pure Blue Emission in Mixed-Halide Perovskite LEDs

Doping Up the Light: A Review of A/B-Site Doping in Metal Halide Perovskite Nanocrystals for Next-Generation LEDs.

All-inorganic metal halide perovskite nanocrystals (PeNCs) show great potential for the next generation of perovskite light-emitting diodes (PeLEDs). However, trap-assisted recombination negatively impacts the optoelectronic properties of PeNCs and prevents their widespread adoption for commercial exploitation. To mitigate trap-assisted recombination and further enhance the external quantum efficiency of PeLEDs, A/B-site doping has been widely investigated to tune the bandgap of PeNCs. The bandgap of PeNCs is adjustable within a small range (no more than 0.1 eV) by A-site cation doping, resulting in changes in the bond length of Pb-X and the angle of [PbX6]4. Nevertheless, B-site doping of PeNCs has a more significant impact on the bandgap level through modification of surface defect states. In this perspective, we delve into the synthesis of PeNCs with A/B-site doping and their impacts on the structural and optoelectronic properties, as well as their impacts on the performance of subsequent PeLEDs. Furthermore, we explore the A-site and B-site doping mechanisms and the impact of device architecture on doped PeNCs to maximize the performance and stability of PeLEDs. This work presents a comprehensive overview of the studies on A-site and B-site doping in PeNCs and approaches to unlock their full potential in the next generation of LEDs.

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.

Enhanced performance of perovskite light-emitting diodes with PEDOT:PSS/CsBr composite hole transport layer

Perovskite light-emitting diodes (PeLEDs) are widely used in optoelectronics due to their excellent performance. The hole transport layer (HTL) plays a crucial role in the performance of the device. In this paper, we prepared quasi-two-dimensional perovskite light-emitting diodes with doping CsBr into PEDOT:PSS as a composite HTL, and investigated the optoelectronic properties of the devices. The maximum luminance of the CsBr-doped device was 6652 cd/m2 and the maximum current efficiency (CE) was 7.55 cd/A, which were increased by 112 % and 80 % compared with the undoped device, respectively. This is primarily due to the PEDOT:PSS/CsBr composite HTL optimizes the morphology of the perovskite film, passivates the defects of the perovskite film, and suppresses the exciton quenching at the HTL/perovskite emission layer (EML) interface. Meanwhile, CsBr doping helps to enhance the hole transport ability of HTL and thus increase the exciton recombination efficiency, which improves the device performance. The results in this paper can provide experimental support for the development of PeLEDs.

Microsecond-response perovskite light-emitting diodes for active-matrix displays

Perovskite light-emitting diodes (PeLEDs) could be of use in the development of active-matrix displays. However, due to ion migration in crystal structure, PeLEDs have electroluminescence rise times over milliseconds, which is problematic for the development of high-refresh-rate displays. Here, we show that the electroluminescence rise time of PeLEDs can be reduced to microseconds using an individual-particle passivation strategy. The approach is based on BF4− ions that can passivate every nanocrystal in a perovskite emissive layer during film deposition. It leads to a defect-free film with discrete nanostructure and excellent crystallinity, which inhibits ion migration. Our strategy can be applied in perovskite nanocrystal films with different colours: red (635 nm), green (520 nm) and blue (475 nm). These PeLEDs all demonstrate response times within microseconds and high external quantum efficiencies of 22.7%, 26.2% and 18.1%, respectively. This allows us to create microsecond-response active-matrix PeLEDs that exhibit external quantum efficiencies above 20% at a display brightness of 500–3,000 cd m−2 for green devices with a resolution of 30 pixels per inch. We also develop microsecond-response red, green and blue active-matrix displays with 90 pixels per inch.

Solvent-Reconstructed Interface That Enhances Light Out-Coupling in Quasi-Two-Dimensional Perovskite Light-Emitting Diodes.

Light management is critical to maximizing the external quantum efficiency of perovskite light-emitting diodes (PeLEDs), but strategies for enhancing light out-coupling are typically complex and expensive. Here, using a facile solvent treatment strategy, we create a layer of lithium fluoride (LiF) nanoislands that serve as a template to reconstruct the light-extracting interfaces for PeLEDs. The nanoisland interface rearranges the near-field light distribution in order to maximize the efficiency of internal light extraction. With the proper adjustment of the nanoisland size and distribution, we have achieved an optimal balance between charge injection and light out-coupling, resulting in bright, pure-red quasi-two-dimensional PeLEDs with a 21.8% peak external quantum efficiency.

Chelation strategy induced blue-shift for efficient deep-blue perovskite light-emitting diodes

Chelation strategy induced blue-shift for efficient deep-blue perovskite light-emitting diodes

Enhancing the Performance of Perovskite Light-Emitting Diodes via Synergistic Effect of Defect Passivation and Dielectric Screening

HighlightsSynergistic passivation mechanism of the dual functional compound of potassium bromide for metal halide perovskite films, that is through chemical bonding and physical screening towards the various types of defects.Metal-ion additives can simultaneously passivate the defects of halide vacancies with bromine anions and dangling bond defects with metal cations.Achieve the maximum external quantum efficiency of ~21% and maximum luminance of ~60,000 cd m−2.

Elevating Charge Transport Layer for Stable Perovskite Light-Emitting Diodes.

Ion migration is a major factor affecting the long term stability of perovskite light-emitting diodes (LEDs), which limits their commercialization potential. The accumulation of excess halide ions at the grain boundaries of perovskite films is a primary cause of ion migration in these devices. Here, it is demonstrated that the channels of ion migrations can be effectively impeded by elevating the hole transport layer between the perovskite grain boundaries, resulting in highly stable perovskite LEDs. The unique structure is achieved by reducing the wettability of the perovskites, which prevents infiltration of the upper hole-transporting layer into the spaces of perovskite grain boundaries. Consequently, nanosized gaps are formed between the excess halide ions and the hole transport layer, effectively suppressing ion migration. With this structure, perovskite LEDs with operational half-lifetimes of 256 and 1774 h under current densities of 100 and 20mAcm-2 respectively are achieved. These lifetimes surpass those of organic LEDs at high brightness. It is further found that this approach can be extended to various perovskite LEDs, showing great promise for promoting perovskite LEDs toward commercial applications.

Folic Acid Passivated Efficient Cerium Doped Perovskite Nanocrystals for High‐Performance Light‐Emitting Diodes

AbstractThe 5d→4f transition of Ce3+ is allowed by the electric dipole and the parity selection rule and the position/intensity of the 5d excited state is strongly dependent on the materials’ composition and atomic structure. Herein, the composition‐dependent luminescence properties of Ce3+ in CsPbCl3‐xBrx (0 ≤ x ≤ 3) perovskite nanocrystals (PeNCs) are systematically revealed. It's observed that the 5d‐4f broadband emission of Ce3+ is greatly improved by optimizing the Cl:Br ratio due to the efficient energy transfer from excitons to Ce3+. Folic acid, a vitamin which is an extremely important cofactor, is introduced to regulate the film formation by interacting with uncoordinated ions. The modified CsPbCl1.5Br1.5 PeNCs with photoluminescence quantum yield of 91% represent a novel and extremely efficient white nanophosphor. Then, white light‐emitting diodes (WLEDs) are constructed by combining Ce3+‐doped PeNCs with 400‐nm ultraviolet chips with a luminous efficiency of 120.3 lm W−1, which is the most efficient perovskite single‐component WLED. Moreover, the blue‐violet LEDs are fabricated with external quantum efficiency of 0.84%, representing extremely high level of 400–435 nm perovskite LEDs. This work demonstrates the strategy in realizing high‐efficiency wavelength‐tunable PeNCs, motivating the further exploration of Ce3+‐doped perovskites in optoelectronic devices.

Acceleration of radiative recombination for efficient perovskite LEDs

The increasing demands for more efficient and brighter thin-film light-emitting diodes (LEDs) in flat-panel display and solid-state lighting applications have promoted research into three-dimensional (3D) perovskites. These materials exhibit high charge mobilities and low quantum efficiency droop1–6, making them promising candidates for achieving efficient LEDs with enhanced brightness. To improve the efficiency of LEDs, it is crucial to minimize nonradiative recombination while promoting radiative recombination. Various passivation strategies have been used to reduce defect densities in 3D perovskite films, approaching levels close to those of single crystals3. However, the slow radiative (bimolecular) recombination has limited the photoluminescence quantum efficiencies (PLQEs) of 3D perovskites to less than 80% (refs. 1,3), resulting in external quantum efficiencies (EQEs) of LED devices of less than 25%. Here we present a dual-additive crystallization method that enables the formation of highly efficient 3D perovskites, achieving an exceptional PLQE of 96%. This approach promotes the formation of tetragonal FAPbI3 perovskite, known for its high exciton binding energy, which effectively accelerates the radiative recombination. As a result, we achieve perovskite LEDs with a record peak EQE of 32.0%, with the efficiency remaining greater than 30.0% even at a high current density of 100 mA cm−2. These findings provide valuable insights for advancing the development of high-efficiency and high-brightness perovskite LEDs.

The synergy of pre-frozen substrates and post-annealing for high-efficiency co-evaporated blue perovskite LEDs

The co-evaporation technique shows great potential for producing perovskite films. However, there is a lack of research on the growth process and the film characteristics of co-evaporated perovskite. Herein, we found that pre-frozen substrates and post-annealing can synergically improve the performance of co-evaporated blue perovskite light-emitting diodes (PeLEDs). The optimized blue PeLEDs obtained an impressive peak external quantum efficiency (EQE) of 7.2%, which is the best reported for co-evaporated blue PeLEDs till now. The systematic investigation found that the pre-frozen substrates can facilitate the exotherm of vaporized precursor molecules near the interface, leading to more efficient nucleation and constraining grain enlargement. Furthermore, low-temperature annealing (LTA) can efficiently suppress compositional segregation and release residual compressive strain in co-evaporated perovskite films while retaining the advantages of pre-frozen substrates. This work provided deeper insights into perovskite films prepared by co-evaporation and offered a feasible strategy for enhancing the performance of the co-evaporated PeLEDs.

Mitigating Perovskite Light-Emitting Diode Degradation Mechanisms through Forward Electrical Pulses

Mitigating Perovskite Light-Emitting Diode Degradation Mechanisms through Forward Electrical Pulses

Pattern‐Matched Polymer Ligpands Toward Near‐Perfect Synergistic Passivation for High‐Performance and Stable Br/Cl Mixed Perovskite Light‐Emitting Diodes

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure‐blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light‐emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter‐functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non‐radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure‐blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1%) and record spectral and operational stabilities (~ 80 mins) in mixed‐halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high‐performance and stable pure‐color PeLEDs towards display applications.

Pattern-Matched Polymer Ligands Toward Near-Perfect Synergistic Passivation for High-Performance and Stable Br/Cl Mixed Perovskite Light-Emitting Diodes.

Mixed Br/Cl perovskite nanocrystals (PeNCs) exhibit bright pure-blue emission benefiting for fulfilling the Rec. 2100 standard. However, phase segregation remains a significant challenge that severely affects the stability and emission spectrum of perovskite light-emitting diodes (PeLEDs). Here, we demonstrate the optimization of the spacing between polydentate functional groups of polymer ligands to match the surface pattern of CsPbBr1.8Cl1.2 PeNCs, resulting in effective synergistic passivation effect and significant improvements in PeLED performances. The block and alternating copolymers with different inter-functional group spacing are facilely synthesized as ligands for PeNCs. Surprisingly, block copolymers with a higher functional group density do not match PeNCs, while alternating copolymers enable efficient PeNCs with the high photoluminescence intensity, low non-radiative recombination rate and high exciton binding energy. Density functional theory calculations clearly confirm the almost perfect match between alternating copolymers and PeNCs. Finally, pure-blue PeLEDs are achieved with the emission at 467 nm and Commission Internationale de l'Eclairage (CIE) coordinates of (0.131, 0.071), high external quantum efficiency (9.1 %) and record spectral and operational stabilities (~80 mins) in mixed-halide PeLEDs. Overall, this study contributes to designing the polymer ligands and promoting the development of high-performance and stable pure-color PeLEDs towards display applications.

Magnetically Induced Near-Infrared Circularly Polarized Electroluminescence from an Achiral Perovskite Light-Emitting Diode

Circularly polarized electroluminescent devices are conventionally fabricated by incorporating an optically active chiral luminophore into their emission layer. Herein, we developed a circularly polarized perovskite light-emitting diode (PeLED) system with an optically inactive perovskite luminophore that can emit near-infrared circularly polarized electroluminescence (CPEL) upon application of an external magnetic field. The magnitude of the magnetic CPEL (gMCPEL) was in the order of 10−3 in the near-infrared wavelength range of 771–773 nm. Although the Pb perovskite quantum dots were achiral, the rotation direction of the CPEL of the magnetic circularly polarized PeLED system was successfully reversed by switching the Faraday geometry of the applied magnetic field. The use of achiral luminophores exhibiting magnetic-field-induced CPEL represents a new approach for the development of circularly polarized electroluminescent devices.

Efficient Perovskite Nanograin Light-Emitting Diodes in Green-to-Blue Gamut with Co-Additive Engineering.

Perovskite nanograins exceeding the Bohr exciton diameter show great potential for high-performance light-emitting diodes (LEDs) owing to their bandgap homogeneity, spatial charge confinement, and nonlocal interaction. However, it is challenging to directly synthesize proper nanograins along with reduced crystal defects on functional substrate, and the corresponding high-efficiency perovskite LEDs (PeLEDs) have rarely been reported. In this study, crystallization modulation for perovskites with an effective co-additive system, including lithium bromide, p-fluorophenethylammonium bromide, and 18-crown-6, is performed. Furthermore, it is demonstrated that the proposed co-additive system can synergistically retard perovskite crystallization and reduce crystal defects. Consequently, high-quality perovskite nanograin solids (≈22.8nm) are obtained with a high photoluminescence quantum yield (≈88%). These superior optical properties contribute to developing efficient green PeLEDs with a champion external quantum efficiency (EQE) of 28.4% and an average EQE of 27.1%. The co-additive system can be universally applied to mixed-halide perovskite nanograin LED, presenting a maximum EQE of 24.4%, 21.6%, 17.5%, and 11.1% for the blue device at 496, 488, 478, and 472nm, respectively, along with a narrow spectral linewidth (17-14nm) and stable color. These results supplement the research on high-efficiency perovskite nanograin LEDs for multicolor displays and lighting.