Perovskite-based Light-emitting Diodes Research Articles

Enhanced light extraction by optimizing near-infrared perovskite-based light emitting diode (PeLED)

One of the outstanding optoelectronic devices is perovskite-based light emitting diodes (PeLEDs) that have diverse applications according to the wavelength of produced light. However, these devices have shown more than 20% External Quantum Efficiency (EQE), in comparison with their counterparts (OLEDs), light extraction is limited in these devices. In this paper, by optimizing the thickness of layers and manipulating absorption in the active layer (AL), the light extraction efficiency (LEE) increased by nearly 20%. It reached 42.89% in the near-infrared (NIR) region of the wavelength, by considering the CH(NH2)2PbI3 perovskite, in the emissive layer (EML).

Defect passivation with spectral shift for improved efficiency and stability of quasi-2D blue perovskite light emitting diodes

Metal halide perovskites are emerging as promising materials for next-generation light-emitting diodes (LEDs), owing to their cost-effectiveness, facile manufacturing, and excellent optoelectronic properties including a narrow emission-line full width at half maximum, high photoluminescence quantum yield, and spectral stability. However, blue-emission perovskite LEDs (PeLEDs) exhibit perovskite phase segregation and halogen ion migration during operation, attributed to crystal defects, halogen vacancies, and phase instability of mixed-halide perovskites. These defects compromise the spectral stability of blue-emitting PeLEDs, resulting in an undesirable color shift toward longer wavelengths. In this study, we introduce a dynamic treatment with phenylphosphonic dichloride (PPOCl2) to address these challenges and achieve blue-emitting PeLEDs. The chloride in PPOCl2 penetrates the quasi-2D sky-blue perovskite, reducing halide defects. Meanwhile, the phosphonic group forms covalent bonds with undercoordinated Pb on the perovskites, effectively passivating defects. PPOCl2-treated perovskite exhibits a spectral blue shift toward a deep-blue wavelength (≤467 nm), enhancing electroluminescence performance. The quasi-2D PPOCl2-treated PeLEDs achieve a maximum external quantum efficiency of 2.31 % with an emission peak at 488 nm. Dynamic treatment with PPOCl2 shows the potential to improve the performance and stability of blue emission perovskite-based LEDs, providing a spectral shift mechanism to achieve deep-blue emission in PeLEDs.

Mitigating thermal burden and enhancing minor phase emission energy transfer in perovskite by introducing dopamine-mediated silver nanoparticles

Perovskite-based light-emitting diodes (PeLEDs) suffer from low wavelength and intensity instability during excited emission. This study incorporates dopamine-mediated silver nanoparticles (DA@AgNPs) into perovskite to enhance the performance of blue-light PeLEDs. Characterization studies highlight the crucial role of dopamine’s hydroxyl group in controlling the size and distribution of AgNPs. Due to the presence of amine group, dopamine acts as a “bridging linker,” facilitating precise integration of AgNPs with perovskite. DA@AgNPs–perovskite comprises a uniform cubic phase, indicating improved crystal quality and fewer defects than in pristine perovskite. DA@AgNPs prevent pinhole-defect-induced heat accumulation, reducing nonradiative energy and Joule heat. Additionally, DA@AgNPs enhance thermal conductivity and thus cooling efficiency. The energy transfer between minor and primary phase emissions is found to be highly efficient and to enhance primary phase emission through the surface plasmon resonance effect of DA@AgNPs. Finally, DA@AgNPs–perovskite is successfully employed in a high-performance blue-light PeLED (wavelength = 476 nm); the device’s external quantum efficiency is 11.2 %, luminance is 380.2 cd/m2, and emission stability is favorable (firmly maintained at 476–478 nm after strong excitation under 4.25 V for 1 h). This work provides insights into one means of improving blue-light PeLEDs, opening avenues for advancements in optoelectronics.

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.

Controlled phase distribution of quasi-2D perovskite enables improved electroluminescence

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.

Spray pyrolysis–deposited NiO film as a hole-injection layer for CsPbBr3 nanocrystal-based light-emitting diodes

In perovskite-based light-emitting diodes (LEDs), employing an inorganic material for the hole-injection layer instead of an organic material is crucial for attaining optimal performance and device stability. This layer needs to exhibit [Formula: see text] -type conductivity with high carrier mobility while being fabricated with a simple and industrially compatible method. In this study, uniform and thin [Formula: see text] -type NiO films were deposited through spray pyrolysis in an air atmosphere. The as-deposited film showed poor crystallinity, and high resistance reduced hole-injection performance. Subsequent thermal treatment at 500∘C enhanced the crystallinity of the layer, reducing resistance and improving LED performance. The film exhibited [Formula: see text] -type semiconductor characteristics, and its carrier mobility, carrier concentration and resistivity were 53.0 × [Formula: see text]cm3, 116cm2⋅ [Formula: see text] and 0.98[Formula: see text] ⋅ [Formula: see text], respectively. Moreover, a compact [Formula: see text] nanocrystal (NC) film as an emitting layer was deposited with a centrifugal coating technique. The resulting LED component featuring a fluoride-doped tin oxide (FTO)/NiO/[Formula: see text] NCs/tris-(1-phenyl-1H-benzimidazole)/LiF/Au structure and demonstrating high luminance, current efficiency and external quantum efficiency (EQE) reached 12,000 cd⋅[Formula: see text], 8.8 cd ⋅ [Formula: see text] and 3.56%, respectively, at 5.5 V. Our work offers a simple and unique approach for accelerating the development of advanced interfacial materials and circumventing major interfacial problems in solution-processed perovskite NC films for high-performance LEDs.

Near-Infrared Light Emitting Metal Halides: Materials, Mechanisms, and Applications.

Near-Infrared (NIR) light emitting metal halides are emerging as a new generation of optical materials owing to their appealing features, which include low-cost synthesis, solution processability, and adjustable optical properties. NIR-emitting perovskite-based light-emitting diodes (LEDs) have reached an external quantum efficiency (EQE) of over 20% and a device stability of over 10,000 h. Such results have sparked an interest in exploring new NIR metal halide emitters. In this review, several different types of NIR-emitting metal halides, including lead/tin bromide/iodide perovskites, lanthanide ions doped/based metal halides, double perovskites, low dimensional hybrid and Bi3+/Sb3+/Cr3+ doped metal halides, are summarized, and their recent advancement is assessed. The characteristics and mechanisms of narrow-band or broadband NIR luminescence in all these materials are discussed in detail. Also, the various applications of NIR-emitting metal halides are highlighted and an outlook for the field is provided.

Phosphine oxide based semiconducting small molecule as an additive and an electron transport layer enables efficient and stable perovskite light-emitting devices

Inclusion of phosphine oxide-based PO-T2T molecule as an additive during perovskite crystallization yields finer perovskite grains and the same molecule acts as an electron transport layer enabling efficient and stable perovskite light emitting diodes.

Highly flexible and stable green perovskite light-emitting diodes based on IL-modified PEDOT:PSS film

Flexible light-emitting diodes (LEDs) are highly sought-after for various applications, such as wearable medical devices, decorative lighting, and flexible displays. Perovskite-based LEDs, due to their low cost, ease of fabrication, and high color purity, have attracted significant attention as promising candidates for modern display technology. However, a primary challenge remains in selecting a bottom anode that provides both high electrical conductivity and optical transmittance while maintaining mechanical robustness to endure rigorous bending. To address this issue, a highly flexible and stable ionic liquid (IL)-modified poly(3,4-ethylene dioxythiophene) polystyrene sulfonate (PEDOT:PSS) bottom anode was developed for high-performance flexible perovskite LEDs (PeLEDs). The addition of 1-ethyl-3-methylimidazolium tetracyanoborate (EMIM TCB) IL initiates a depth-dependent rearrangement of the PEDOT and PSS moieties within the PEDOT:PSS film and improves its conductivity by orders of magnitude. Additionally, the IL increases the work function of the PEDOT:PSS layer, leading to a reduced barrier for hole injection. The fabricated flexible green PeLEDs exhibited pure green emission at 520 nm with a maximum external quantum efficiency (EQE) of 11.6% and maximum luminance of 25566.8 cd/m2. Remarkably, the device retained 85% of its initial luminance after 5000 bending cycles at a 5 mm bending radius.

Mask-Free Patterned Perovskite Microcavity Arrays via Inkjet Printing Targeting Laser Emission.

Perovskite materials are promising candidates for the implementation of electrically pumped lasers considering the enhanced performance of perovskite-based light-emitting diodes. Nonetheless, current methods of fabricating perovskite optical microcavities require complex patterning technologies to build suitable resonant cavities for perovskite laser emission, burdening the device structure design. To address this issue, we applied inkjet printing, a maskless patterning technique, to directly create spontaneous formations of polycrystalline perovskite microcavity arrays to explore their laser-emitting action. The substrate surface tension was tuned to modulate the perovskite crystallization process in combination with optimization of printing ink recipes. As a result, polycrystalline perovskite microcavity arrays were achieved, contributing to the laser emission at 528 nm with a lasing threshold of 1.37 mJ/cm2, while simultaneously achieving high-definition patterning of flexible display. These results clearly illustrate the efficiency of inkjet printing technology in the preparation of polycrystalline perovskite optical microcavities and promote the development of flexible laser arrayed displays, providing a facile process toward the realization of perovskite-cavity laser devices.

Fully Inkjet‐Printed Green‐Emitting PEDOT:PSS/NiO/Colloidal CsPbBr3/SnO2 Perovskite Light‐Emitting Diode on Rigid and Flexible Substrates

After establishing themselves as promising active materials in the field of solar cells, halide perovskites are currently being explored for fabrication of low‐cost, easily processable, and highly efficient light‐emitting diodes (LEDs). Despite this, the highest efficiencies reported for perovskite‐based LEDs (PeLEDs) are achieved through spin coating or vacuum evaporation deposition techniques, which are not adequate, in most of the cases, for an industrial‐scale production. Additionally, the long‐term stability is still a big handicap, even though all inorganic perovskites, such as CsPbBr3, are found to be more stable to external variables. In this context, herein, the fabrication of fully inkjet‐printed (IJP) CsPbBr3‐based PeLEDs in ambient conditions, on rigid and flexible substrates, on a proof‐of‐concept basis, with the successful incorporation of NiO and SnO2 as hole‐ and electron‐selective contacts, respectively, is reported. Despite the moderate luminance (324 cd m−2) value obtained, this result paves the way toward the development of upscalable fabrication of PeLEDs based on deposition techniques with controlled spatial resolution.

Materials, Device Structures, and Applications of Flexible Perovskite Light‐Emitting Diodes

AbstractThe flexible type of displays, which can alter their shape freely (e.g., bendable or foldable displays) according to situational demands, is under an intense spotlight due to applications in human‐friendly mobile electronics. Among various types of light‐emitting diodes (LEDs), meanwhile, perovskite‐based LEDs (PeLEDs) have garnered particular attention in recent years as next‐generation optoelectronic devices due to their exceptional optical characteristics, such as high efficiency (up to theoretical limits), high color purity, wide color gamut over the entire visible range, and ultrathin form factor. By integrating perovskite materials on an ultrathin flexible substrate with a proper encapsulation layer, the flexible PeLEDs, which can conform to various curved surfaces and be stably operated in an ambient condition, have been developed. Here, recent advances of the flexible PeLEDs are reviewed. First, light‐emitting materials and device structures for the PeLEDs are introduced. Then, research progress on the flexible PeLEDs, either with and without the encapsulation layer are summarized. Next, some representative application examples of the flexible PeLEDs are briefly discussed. Finally, this review includes a brief discussion on future prospects.

Efficient and Bright Deep-Red Light-Emitting Diodes based on a Lateral 0D/3D Perovskite Heterostructure.

Bright and efficient deep-red light-emitting diodes (LEDs) are important for applications in medical therapy and biological imaging due to the high penetration of deep-red photons into human tissues. Metal-halide perovskites have potential to achieve bright and efficient electroluminescence due to their favorable optoelectronic properties. However, efficient and bright perovskite-based deep-red LEDs have not been achieved yet, due to either Auger recombination in low-dimensional perovskites or trap-assisted nonradiative recombination in 3D perovskites. Here, a lateral Cs4PbI6/FAxCs1- xPbI3 (0D/3D) heterostructure that can enable efficient deep-red perovskite LEDs at very high brightnessis demonstrated. The Cs4PbI6 can facilitate the growth of low-defect FAxCs1- xPbI3, and act as low-refractive-index grids, which can simultaneously reduce nonradiative recombination and enhance light extraction. This device reaches a peak external quantum efficiency of 21.0% at a photon flux of 1.75×1021 m-2 s-1, which is almost two orders of magnitude higher than that of reported high-efficiency deep-red perovskite LEDs. Theses LEDs are suitable for pulse oximeters, showing an error <2% of blood oxygen saturation compared with commercial oximeters.

Core/Shell ZnO/ZnS Nanoparticle Electron Transport Layers Enable Efficient All-Solution-Processed Perovskite Light-Emitting Diodes.

Solution-processed perovskite-based light-emitting diodes (PeLEDs) are promising candidates for low-cost, large-area displays, while severe deterioration of the perovskite light-emitting layer occurs during deposition of electron transport layers from solution in an issue. Herein, core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer in PeLED based on quasi-2D PEA2 Csn-1 Pbn Br3n+1 (PEA = phenylethylammonium) perovskite are employed. The deposition of ZnS shell mitigates trap states on ZnO core by anchoring sulfur to oxygen vacancies, and at the same time removes residual hydroxyl groups, which helps to suppress the interfacial trap-assisted non-radiative recombination and the deprotonation reaction between the perovskite layer and ZnO. The core/shell ZnO/ZnS nanoparticles show comparably high electron mobility to pristine ZnO nanoparticles, combined with the reduced energy barrier between the electron transport layer and the perovskite layer, improving the charge injection balance in PeLEDs. As a result, the optimized PeLEDs employing core/shell ZnO/ZnS nanoparticles as a solution-processed electron transport layer exhibit high peak luminance reaching 32400cdm-2 , external quantum efficiency of 10.3%, and 20-fold extended longevity as compared to the devices utilizing ZnO nanoparticles, which represents one of the highest overall performances for solution-processed PeLEDs.

In Situ Halide Exchange of Cesium Lead Halide Perovskites for Blue Light-Emitting Diodes.

3D perovskites are promising to achieve efficient and bright deep-blue light-emitting diodes (LEDs), which are required for lighting and display applications. However, the efficiency of deep-blue 3D perovskite-based LEDs is limited by high density of defects in perovskites, and their deep-blue emission is not easy to achieve due to the halide phase separation and low solubility of chloride in precursor solutions. Here, an in situ halide exchange method is developed to achieve deep-blue 3D perovskites by spin-coating an organic halide salts solution to treat blue 3D perovskites. It is revealed that the halide-exchange process is mainly determined by halide ion diffusion targeting a concentration equalization, which leads to homogeneous 3D mixed-halide perovskites. By further introducing multifunctional organic ammonium halide salts into the exchange solution to passivate defects, high-quality deep-blue perovskites with reduced trap density can be obtained. This approach leads to efficient deep-blue perovskite LEDs with a peak external quantum efficiency (EQE) of 4.6% and a luminance of 1680cdm-2 , which show color coordinates of (0.131, 0.055), very close to the Rec. 2020 blue standard. Moreover, the halide exchange method is bidirectional, and blue perovskite LEDs can be achieved with color coordinates of (0.095, 0.160), exhibiting a high EQE of 11.3%.

Quantum‐Confined Dodecahedron CsPbBr3 Quantum Dots by A Sequential Post‐Treatment Strategy for Efficient Blue PeLEDs

AbstractCsPbBr3 quantum dots (QDs) prepared through traditional hot‐injection and room temperature reprecipitation methods are usually hexahedral (nanoplate/cube) and green‐emitting. These methods severely obstruct the development of blue perovskite‐based light‐emitting diodes (PeLEDs) because the resultant QDs always suffer unachievable morphology regulation. Here, highly efficient blue‐emitting rhombic dodecahedron CsPbBr3 QDs (CsPbBr3 &lt;12&gt; QDs) are obtained by regulating morphological transformation for the first time through a novel and facile sequential post‐treatment strategy. Hydrobromide (‐NH3+) with stronger adsorption energy promotes the morphology transform of QDs from nanoplate to cube by substituting oleylamine in the first step. Then, polar solvent vapor eliminates PbX64− and led to the (112) crystal plane of the cube QDs being exposed, which is effectively stabilized by ‐NH3+ to realize morphology transition from cube to the dodecahedron. Highly efficient 12‐faceted dodecahedrons are endowed with significantly enhanced photoluminescence quantum yield of 89.8% at 476 nm as well as uniform size distribution and mono‐dispersity. The target blue PeLEDs achieve the maximum external quantum efficiency of 6.6% (480 nm) and excellent spectrum stability. This study provides a new strategy to prepare blue‐emitting CsPbBr3 &lt;12&gt; QDs by delicate control toward the growth and polyhedron process of crystal.

Effective passivation of perovkiste grain boundaries by a carboxylated polythoiphene for bright and stable Pure-Red perovskite light emitting diodes

High luminance and operative stability are essential parameters for realizing the commercialization of perovskite-based light-emitting diodes (PLEDs). However, the optoelectronic properties of PLEDs are still limited owing to the un-optimized charge transport behavior of perovskite films arising from severe defect densities and imperfect lattice structure at grain boundaries. To retrieve the morphological imperfection, we herein suggest a carboxylated polythiophene (P3CT) as a novel passivating agent of perovskite films in PLEDs. The carboxylic acid groups of P3CT enable Lewis acid-base interactions with the defective surface of perovskites such as under-coordinated Pb2+ sites or halide deficiencies, leading to efficient defect passivation and stabilization of the perovskite film surface. The P3CT-passivation successfully fabricates pinhole-free perovskite films with diminished defects at grain boundaries, bringing enhanced optoelectronic properties of red electroluminescence EL emission with a peak current efficiency and external quantum efficiency (EQE) values up to 11.15 % and 4 %, respectively. Moreover, the operative stability of the passivated PLEDs is markedly improved due to the stabilization and increased hydrophobicity of perovskite films by the inclusion of P3CT. The present findings provide a new perspective for developing stable red-PLEDs with efficient luminescence.

Elimination of unexpected destruction on CsPbBrxI3-x nanocrystals arising from polymer matrix

Cesium lead halide perovskite (CsPbX3) nanocrystals (NCs) have exhibited promising applications in light-emitting diodes (LEDs) due to their tunable bandgap and high quantum efficiency. Backlighting LEDs based on CsPbBr3 NCs with green emission have been widely designed to show their superiority. However, unlike CsPbBr3 NCs, backlighting LEDs composed of mixed-halide perovskite (CsPbBrxI3-x) NCs have rarely been reported and should be further applied in colorful LEDs for granted, mainly because of the unexpected destructive effects from the commercial polymer matrix verified in this work. Purification of a commercial polymer matrix was promoted as an effective method to eliminate the destructive effects. Further investigation proved that the species with strong polarity and oxidability, e.g., BPO in commercial PMMA, are responsible for such destructive effects by inducing the structural transformation of CsPbBrxI3-x NCs. We believe such results can help to gain a deeper understanding of the degradation mechanism of mixed-halide perovskite materials and indicate a promising method to develop stable colorful perovskite-based LEDs.

Diammonium-Mediated Perovskite Film Formation for High-Luminescence Red Perovskite Light-Emitting Diodes.

3D mixed-halide perovskite-based red emitters combine excellent charge-transport characteristics with simple solution processing and good film formation; however, light-emitting diodes (LEDs) based on these emitters cannot yet outperform their nanocrystal counterparts. Here the use of diammonium halides in regulating the formation of mixed bromide-iodide perovskite films is explored. It is found that the diammonium cations preferentially bond to Pb-Br, rather than Pb-I, octahedra, promoting the formation of quasi-2D phases. It is proposed that the perovskite formation is initially dominated by the crystallization of the thermodynamically more favorable 3D phase, but, as the solution gets depleted from the regular A cations, thin shells of amorphous quasi-2D perovskites form. This leads to crystalline perovskite grains with efficiently passivated surfaces and reduced lattice strain. As a result, the diammonium-treated perovskite LEDs demonstrate a record luminance (10745cd m-2 ) and half-lifetime among 3D perovskite-based red LEDs.

Effect of silica encapsulation on the stability and photoluminescence emission of FAPbI3 nanocrystals for white-light-emitting perovskite diodes

The α-FAPbI 3 perovskite nanocrystals exhibit interesting optical properties, which make them attractive for versatile optoelectronic applications; however, the spontaneous phase transformation to the non-perovskite phase (δ-FAPbI 3 ) in humid conditions requires a new strategy to improve the phase stability of the material. We employed 3-Aminopropyl triethoxysilane (APTES)-assisted reprecipitation and sol-gel methods at ambient temperature to prepare stable α-FAPbI 3 nanocrystals embedded in a silica matrix. Transmission electron microscopy (TEM) and X-ray diffraction analysis determined that ultrafine perovskite nanocrystals (11.5 ± 3 nm) were uniformly distributed in a silica matrix. Investigations of the optical properties of the synthesized materials revealed that about 94% of the photoluminescence (PL) emission of silica-encapsulated FAPbI 3 nanocrystals was preserved under humid conditions (60%) after at least a month, while the PL emission of untreated FAPbI 3 was significantly decayed after few days. The thermal analysis also determined that the thermal stability of FAPbI 3 nanocrystals was improved by silica encapsulation. The red-emitting silica-encapsulated FAPbI 3 nanocrystals with a wavelength of 720 nm were used to fabricate white light-emitting diodes (LEDs) in a vertical structure consisting of a blue-chip, PMMA/CsPbBr 3 QDs, and PMMA/FAPbI 3 -SiO 2 QDs. Stable perovskite-based white LEDs with a color gamut of 144% NTSC were fabricated, which was better than many phosphor-based and perovskite-based LEDs. The synthesized composite perovskite nanocrystals could be used for next-generation optoelectronic devices. • Synthesis of silica-encapsulated FAPbI 3 quantum dots at ambient temperature by a combined LARP and sol-gel process. • Minor PL intensity loss in the humidified atmosphere after few months. • WLEDs with a high color gamut of 144% NTSC. • A pure red LED with coordination (0.729, 0.270).