Perovskite Emissive Layer Research Articles

Efficient all-inorganic red perovskite light-emitting diodes with dual-interface-modified perovskites by vapor deposition.

Interface engineering has been extensively used in perovskite light-emitting diodes (PeLEDs), which proves to be an effective and intelligent approach for surface defect passivation. However, the existing passivation strategy is restricted to the solution process, which results in poor compatibility with vapor-deposited PeLEDs and moderate controllability. Here, we propose a dual-interface modification strategy to facilitate the performance improvement of vapor-deposited all-inorganic red PeLEDs. An ultrathin phenylethanamine bromide (PEABr) layer is introduced to both the upper and lower interfaces of the vapor-deposited perovskite emission layer by vapor deposition. The vapor deposition of the PEABr with fine-controlled film thickness is a reliable and simple process and compatible with vapor-deposited all-inorganic PeLEDs. The dual-interface modification plays an observable role in manipulating the crystallization and surface morphology of the CsPbBrI2 film, which is of significance for the improvement of the PeLEDs' performance. As a result, the red PeLEDs achieve a maximum luminance and external quantum efficiency of 2338 cd/m2 and 1.75%, corresponding to enhancements of 2.75 and 5.25 times compared with those of PeLEDs without PEABr. This approach paves the way to high-efficiency all-evaporated all-inorganic PeLEDs.

High Triplet Energy Level Molecule Enables Highly Efficient Sky-Blue Perovskite Light-Emitting Diodes.

The role of triplet states in the interfacial energy transfer in perovskite light-emitting diodes (PeLEDs) has so far not been clarified because of the complex exciton recombination and decay dynamics. This work aims to study this issue and accordingly proposes a novel interfacial-engineering strategy for efficient sky-blue PeLEDs. To this end, bis[2-(diphenylphosphino)phenyl]ether oxide with a high triplet energy level is introduced into sky-blue PeLEDs. It effectively reduces undesirable exciton transfer from the perovskite emission layer to the electron-transport layer, largely suppresses exciton quenching at the interface, and simultaneously passivates defects at the perovskite surfaces. As a result of the multichannel energy-loss reduction, sky-blue PeLED that emits at 488 nm is achieved with a peak external quantum efficiency of 10.17% and a maximum brightness of 6728.41 cd m-2. This work thus provides indirect evidence for the triplet mechanism of blue emission of mixed-halide perovskites and sheds new light on a promising way of boosting the performance of blue PeLEDs.

Perovskite Light-Emitting Electrochemical Cells Employing Electron Injection/Transport Layers of Ionic Transition Metal Complexes.

Recently, perovskites have attracted intense attention due to their high potential in optoelectronic applications. Employing perovskites as the emissive materials of light-emitting electrochemical cells (LECs) shows the advantages of simple fabrication process, low-voltage operation, and compatibility with inert electrodes, along with saturated electroluminescence (EL) emission. Unlike in previously reported perovskite LECs, in which salts are incorporated in the emissive layer, the ion-transport layer was separated from the emissive layer in this work. The layer of ionic transition metal complex (iTMC) not only provides mobile ions but also serves as an electron-injection/transport layer. Orthogonal solvents are used in spin coating to prevent the intermixing of stacked perovskite and iTMC layers. The blue iTMC with high ionization potential is effective in blocking holes from the emissive layer and thus ensures EL color saturation. In addition, the carrier balance of the perovskite/iTMC LECs can be optimized by adjusting the iTMC layer thickness. The optimized external quantum efficiency of the CsPbBr3 /iTMC LEC reaches 6.8 %, which is among the highest reported values for perovskite LECs. This work successfully demonstrates that, compared with mixing all components in a single emissive layer, separating the layer of ion transport, electron injection and transport from the perovskite emissive layer is more effective in adjusting device carrier balance. As such, solution-processable perovskite/iTMC LECs open up a new way to realize efficient perovskite LECs.

H2O treatment-induced uniform NiOX interfacial layer boosting brightness and light-emitting efficiency of blue perovskite electroluminescence

The reported NiO x interfacial layers in blue perovskite light-emitting diodes (PeLEDs) usually require high-temperature annealing and complex interface modification. Herein, we report a kind of uniform NiO x anode interfacial layer induced by H 2 O treatment, which effectively enhances the brightness and light-emitting efficiency of blue PeLEDs simultaneously. Compared to the as-prepared NiO x anode interfacial layer, H 2 O treatment renders uniform and pinhole-free NiO x morphology. The solution-processed perovskite blue emissive layer prepared atop the H 2 O-treated NiO x interfacial layer demonstrates enhanced photoluminescent property and superior morphology with low trap density. The blue PeLEDs employing H 2 O-treated NiO x as anode interfacial layer show a maximum luminance of 9052 cd/m 2 and a maximum external quantum efficiency (EQE) of 1.80%, whereas the control device based on the as-prepared NiO x anode interfacial layer merely exhibits a maximum luminance of 3850 cd/m 2 and an EQE of 0.88%, leading to about 135% and 104% increase in brightness and efficiency, respectively. The PeLEDs emit pure blue light with emission peak located at 482 nm and demonstrate superior spectral stability under different driving voltages and operating time. • High-brightness blue PeLEDs were fabricated using NiO x interfacial layer. • H 2 O-treated NiO x interfacial layer induces to form high-quality blue perovskite emissive layer. • The blue PeLEDs attain a maximum luminance of 9052 cd/m 2 and a maximum EQE of 1.80%. • The PeLEDs emit stable blue light with emission peak at 482 nm.

A Generic Protocol for Highly Reproducible Manufacturing of Efficient Perovskite Light‐Emitting Diodes Using In‐Situ Photoluminescence Monitoring

AbstractHalide perovskite light‐emitting diodes (PLEDs) have raised considerable attention due to their high color purity and rapid development performance. Although high‐efficiency PLEDs have been continuously and repeatedly reported, the lack of a highly reproducible manufacturing process for PLEDs hinders their future development and commercialization. Here, a generic protocol for rational control of the nucleation and crystallization process of the perovskite emission layer is reported. Through the monitoring of the photoluminescence during spin‐coating, the antisolvent dripping time can be precisely determined. Therefore, it is possible to repeatedly produce a perovskite emission layer with high PLQY, smooth surface/interface, and good homogeneity. As a result, high‐performance PLEDs are easily obtained. Moreover, the standard deviation of the fabricated PLEDs performance is smaller than 0.8%, showing high reproducibility independent of the process conditions such as the process temperature, solvent atmosphere, and spin‐coating parameters, which highlights the statement of the importance of rationally control of the antisolvent process. The methodology provides important progress towards highly reproducible manufacturing of PLEDs for practical applications.

High-Speed Fabrication of All-Inkjet-Printed Organometallic Halide Perovskite Light-Emitting Diodes on Elastic Substrates.

Halide perovskites have great potential for use in high-performance light-emitting diodes (LEDs) and displays. Here, a perovskite LEDs (PeLEDs) fabricated directly on an elastomer substrate, in which every single layer in the device from bottom anode to top cathode is patterned solely using a highly scalable inkjet printing process, is reported. Compared to PeLEDs made using conventional microfabrication processes, the printing process significantly shortens the fabrication time by at least tenfold (from over 5 h to less than 25 min). The all-printed PeLEDs have a novel 4-layer structure (bottom electrode, perovskite emissive layer, buffer layer, top electrode) without separate electron or hole transporting layers. For flexible PeLEDs printed directly in ambient conditions, a turn-on voltage, maximum luminance intensity, and maximum current efficiency of 3.46V, 10227cdm-2 , and 2.01cdA-1 , respectively, is achieved. The devices also exhibit excellent robustness and stability even when bent to a curvature radius of 2.5mm. The reported device structure and fabrication processes can enable high-performance flexible PeLEDs to be manufactured over a larger area at extremely low cost and fast speed, which can facilitate the adoption of the promising PeLED technology in the emerging foldable displays, smart wearables, and many other applications.

Mn2+‐Doped CsPbI3 Nanocrystals for Perovskite Light‐Emitting Diodes with High Luminance and Improved Device Stability

Cubic α‐CsPbI3 has promising applications in the optoelectronic field for its excellent properties. However, α‐CsPbI3 black phase is instable at room temperature and easily converts into nonluminescent yellow orthorhombic phase (δ‐CsPbI3). Herein, the stability of α‐CsPbI3 is significantly improved by incorporating Mn2+ dopants into the perovskite lattice. Mn2+: CsPbI3 has essentially the same crystal structure as the parent α‐CsPbI3, and Mn2+ doping can promote photoluminescence quantum yield (PLQY) from 55% to 93%. Importantly, Mn2+: CsPbI3 can maintain 60% PLQY after exposing in air for 45 days, whereas the undoped CsPbI3 completely loses its luminescence in 10 days. First‐principles calculations testify that improved stability and optical properties of Mn2+: CsPbI3 are primarily attributed to the increased formation energy and tolerance factor. Accordingly, the luminance, external quantum efficiency (EQE), and T 50 lifetime of Mn2+: CsPbI3 perovskite light‐emitting diode (PeLED) reach 1066 cd m−2, 1.8%, and 2500 s, whereas the values for the undoped counterpart are only 415 cd m−2, 0.6%, and 140 s, respectively. In addition, it is evidenced that introducing a LiF buffer layer between hole transport layer and perovskite emissive layer can further boost the device performance, particularly, the luminance and T 50 lifetime achieve 1394 cd m−2 and 225 min at 140 cd m−2.

Perovskite light-emitting diodes with low roll-off efficiency via interfacial ionic immobilization

Metal halide perovskite light-emitting diodes (PeLEDs) are emerging low-cost solution-processable technology with high color purity and tunable emission wavelength. However, the defective interface between perovskite emission layer and charge transport layer substantially limits the improvement of device performance, especially for a device with simultaneously high luminance and decent external quantum efficiency. Herein, we propose a facile and reliable interfacial modification strategy to realize efficient PeLEDs with high external quantum efficiency under high luminance. By modifying the hole transport layer with alkali metal ions (K+, Na+) and weak acid ion (citrate ion), perovskite films with high surface coverage and fewer interface defects are fabricated. As a result, a high brightness of 80,288 cd/m2 and a high external quantum efficiency of 13.02% under continuous current drive are obtained in our PeLEDs. More commendable, our devices show low roll-off behaviors of EQE under high luminance and high current density, because of halide anion and lead cation vacancies at the interface of perovskite and charge transport layer are efficiently suppressed.

Critical role of additive-induced molecular interaction on the operational stability of perovskite light-emitting diodes

Summary Despite rapid improvements in efficiency and brightness of perovskite light-emitting diodes (PeLEDs), the poor operational stability remains a critical challenge hindering their practical applications. Here, we demonstrate greatly improved operational stability of high-efficiency PeLEDs, enabled by incorporating dicarboxylic acids into the precursor for perovskite depositions. We reveal that the dicarboxylic acids efficiently eliminate reactive organic ingredients in perovskite emissive layers through an in situ amidation process, which is catalyzed by the alkaline zinc oxide substrate. The formed stable amides prohibit detrimental reactions between the perovskites and the charge injection layer underneath, stabilizing the perovskites and the interfacial contacts and ensuring the excellent operational stability of the resulting PeLEDs. Through rationally optimizing the amidation reaction in the perovskite emissive layers, we achieve efficient PeLEDs with a peak external quantum efficiency of 18.6% and a long half-life time of 682 h at 20 mA cm−2, presenting an important breakthrough in PeLEDs.

Interface and bulk controlled perovskite nanocrystal growth for high brightness light-emitting diodes [Invited

Halide perovskites have attracted great attention due to their high color purity, high luminance yield, low non-radiative recombination rate, and solution processability. Although the external quantum efficiency of perovskite light-emitting diodes (PeLEDs) is comparable with that of the organic light-emitting diodes (OLEDs) and quantum-dots light-emitting diodes (QLEDs), the brightness is still low compared with the traditional OLEDs and QLEDs. Herein, we demonstrate high brightness and high-efficiency CsPbBr3-based PeLEDs using interface and bulk controlled nanocrystal growth of the perovskite emission layer. The interface engineering by ethanolamine and bulk engineering by polyethylene glycol led to highly crystallized and cubic-shaped perovskite nanocrystals with smooth and compact morphology. As a result, PeLEDs with a high brightness of 64756 cd/m2 and an external quantum efficiency of 13.4% have been achieved.

Boosting the Efficiency and Stability of Perovskite Light-Emitting Devices by a 3-Amino-1-propanol-Tailored PEDOT:PSS Hole Transport Layer.

Properties of the underlying hole transport layer (HTL) in perovskite light-emitting devices (PeLEDs) play a critical role in determining the optoelectronic performance through influencing both the charge transport and the quality of the active perovskite emission layer (EML). This work focuses on manipulating the carrier transport behavior and obtaining a high-quality EML film by tailoring the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) HTL with previously unused amino alcohol 3-amino-1-propanol (3AP). The modified PEDOT:PSS rendered a deeper work function that is more suitable for the hole injection from the HTL to EML. More importantly, the 3AP-modified PEDOT:PSS film can induce a low-dimensional perovskite phase that can passivate the defects in the EML, resulting in a significantly improved light emission. Such ameliorations consequently result in a dramatical enhancement in performance of PeLED with a low turn-on voltage of 2.54 V, a maximum luminance of 23033 cd/m2, a highest current efficiency of 29.38 cd/A, a corresponding maximum external quantum efficiency of 9.4%, and a prolonged lifetime of 6.1 h at a proper Cs/Pb ratio.

Improved performance of perovskite light-emitting device with urea modified PEDOT:PSS hole transport layer

Efficient perovskite light-emitting devices (PeLEDs) was obtained by tailoring hole transport layer (HTL) PEDOT:PSS with urea. The urea-modulated PEDOT:PSS exhibited better conductivity and deeper work function (WF) compared with the neat PEDOT:PSS, enabling efficient charge injection from the HTL to the perovskite emission layer. The luminescent quenching resulted from the interfacial defects was also effectively suppressed. Such merits consequently result in reduced turn on voltage, promoted brightness, improved current efficiency (CE) and corresponding external quantum efficiency (EQE). By further passivating the bulk defects in the CsPbBr3 films by polyethylene glycol (PEG), a maximum brightness of 26487 cd/m2, a peak CE of 16.68 cd/A and a maximum EQE of 4.84% were achieved.

Facile Fabrication of Stretchable Touch-Responsive Perovskite Light-Emitting Diodes Using Robust Stretchable Composite Electrodes.

Perovskite light-emitting diode (PeLED) has been vigorously developed in recent years. As it has demonstrated good performance on the rigid substrates, the next important direction of PeLED is its integration with stretchable components to realize stretchable, responsive device. Here, we describe a facile fabrication of stretchable perovskite light-emissive touch-responsive devices (PeLETDs) by utilizing highly transparent and conductive polyurethane/silver nanowires (PU/AgNWs) as the electrode. Meanwhile, a stretchable tricomposite perovskite emissive layer was developed by blending a small amount of poly(ethylene oxide) (PEO) and poly(vinylpyrrolidone) (PVP) with CsPbBr3. Additionally, a thin PVP layer was introduced at the bottom of the emissive layer. On one hand, it can further improve the morphology of the emissive layer; on the other hand, it can serve as an electron-injection barrier to reduce the high nonradiative recombination at the corresponding interface. Further, to fulfill the responsive function of the fabricated PeLEDs, a poly(ethylene terephthalate) (PET) spacer with a 100 μm thickness was inserted between the top electrode and the emissive layer. A stretchable PeLETD is finally demonstrated to possess a low turn-on voltage of 2 V with a brightness of 380.5 cd m-2 at 7.5 V and can sustain 30% uniaxial strain with a small luminance variation of 24%. More interestingly, our stretchable PeLETD exhibited high stability, which could be well touch responsivity, where the luminance is on/off switched for 300 cycles by repeatedly applying pressure.

Reduced Efficiency Roll‐Off and Improved Stability of Mixed 2D/3D Perovskite Light Emitting Diodes by Balancing Charge Injection

AbstractPerovskite light emitting diodes (PeLEDs) have reached external quantum efficiencies (EQEs) over 21%. Their EQE, however, drops at increasing current densities (J) and their lifetime is still limited to just a few hours. The mechanisms leading to EQE roll‐off and device instability require thorough investigation. Here, improvement in EQE, EQE roll‐off, and lifetime of PeLEDs is demonstrated by tuning the balance of electron/hole transport into a mixed 2D/3D perovskite emissive layer. The mixed 2D/3D perovskite layer induces exciton confinement and beneficially influences the electron/hole distribution inside the perovskite layer. By tuning the electron injection to match the hole injection in such active layer, a nearly flat EQE for J = 0.1–200 mA cm−2, a reduced EQE roll‐off until J = 250 mA cm−2, and a half‐lifetime of ≈47 h at J = 10 mA cm−2 is reached. A model is also proposed to explain these improvements that account for the spatial electron/hole distributions.

Perovskite Light-Emitting Diodes with Improved Outcoupling Using a High-Index Contrast Nanoarray.

Organic-inorganic hybrid perovskite light-emitting diodes (PeLEDs) are promising for next-generation optoelectronic devices due to their potential to achieve high color purity, efficiency, and brightness. Although the external quantum efficiency (EQE) of PeLEDs has recently surpassed 20%, various strategies are being pursued to increase EQE further and reduce the EQE gap compared to other LED technologies. A key point to further boost EQE of PeLEDs is linked to the high refractive index of the perovskite emissive layer, leading to optical losses of more than 70% of emitted photons. Here, it is demonstrated that a randomly distributed nanohole array with high-index contrast can effectively enhance outcoupling efficiency in PeLEDs. Based on a comprehensive optical analysis on the perovskite thin film and outcoupling structure, it is confirmed that the nanohole array effectively distributes light into the substrate for improved outcoupling, allowing for 1.64 times higher light extraction. As a result, highly efficient red/near-infrared PeLEDs with a peak EQE of 14.6% are demonstrated.

Highly bright and stable all-inorganic perovskite light-emitting diodes with methoxypolyethylene glycols modified CsPbBr3 emission layer

Modifying the inorganic perovskite emission layer (EML) with polymer materials is one of the key strategies to improve the performance of perovskite light-emitting diodes (PeLEDs). However, the reported polymers, such as polyethylene glycol (PEG), typically have poor solubility in solvents [like dimethylsulfoxide (DMSO)] of perovskite precursors, which requires a pre-heating process to dissolve them. Here, methoxypolyethylene glycol (mPEG), which possesses high solubility in DMSO, is introduced into the perovskite precursors without pre-heating. The highest luminance of 33 500 cd m−2 and the maximum current efficiency of 3.14 cd A−1 are achieved in the prepared PeLED by optimizing the mPEG content in the CsPbBr3 EML, which are even better than those of the PeLEDs modified with PEG. Moreover, the optimized PeLED shows a sub-bandgap turn-on voltage of 2.3 V, which is among the lowest values of single polymer-assisted all-inorganic PeLEDs. The device stability of PeLEDs is also improved by mPEG doping in the CsPbBr3 EML, which shows no obvious decay after operating at an initial luminance of 100 cd m−2 for more than 150 min and 24 h for bare and encapsulated devices, respectively. Our work reveals the great potential of the polymer, mPEG, in modifying the CsPbBr3 EML film for highly bright and stable PeLEDs.

High-efficiency, solution-processable, multilayer triple cation perovskite light-emitting diodes with copper sulfide–gallium–tin oxide hole transport layer and aluminum-zinc oxide–doped cesium electron injection layer

Light-emitting diodes with perovskite luminophores have great potential in next-generation displays because of their exceptional color purity with narrow emission bandwidth, broadband color tunability, and solution processability. However, their low luminescent efficiency is a critical drawback. Here, we report the first demonstration of a multicolor, large-area, perovskite display, which can be made flexible by using an optimized perovskite emissive layer sandwiched between inorganic metal oxide charge transport layers, all of which are coated via a facile solution process. We show that advanced interfacial engineering, especially the energy level alignment at the interface, plays a vital role in determining the device performance because of its effects on charge injection, transport, and recombination. These devices exhibit maximum current and power efficiencies of 74.25 cd A−1 and 89.72 lm/w for green emission, 21.40 cd A−1 and 25.84 lm/w for red emission, and 15.21 cd A−1 and 15.84 lm/w for blue emission, respectively. Furthermore, with the introduction of inorganic charge transport layers, these devices exhibit high environmental stability, and the encapsulated devices have operating lifetimes exceeding 450 h with an initial brightness of 1000 cd/m2.

Boosting Perovskite Light-Emitting Diode Performance via Tailoring Interfacial Contact.

Solution-processed perovskite light-emitting diodes (LEDs) have attracted wide attention in the past several years. However, the overall efficiency and stability of perovskite-based LEDs remain inferior to those of organic or quantum dot LEDs. Nonradiative charge recombination and the unbalanced charge injection are two critical factors that limit the device efficiency and operational stability of perovskite LEDs. Here, we develop a strategy to modify the interface between the hole transport layer and the perovskite emissive layer with an amphiphilic conjugated polymer of poly[(9,9-bis(3'-( N, N-dimethylamino)propyl)-2,7-fluorene)- alt-2,7-(9,9-dioctylfluorene)] (PFN). We show evidences that PFN improves the quality of the perovskite film, which effectively suppresses nonradiative recombination. By further improving the charge injection balance rate, a green perovskite LED with a champion current efficiency of 45.2 cd/A, corresponding to an external quantum efficiency of 14.4%, is achieved. In addition, the device based on the PFN layer exhibits improved operational lifetime. Our work paves a facile way for the development of efficient and stable perovskite LEDs.

Fast Postmoisture Treatment of Luminescent Perovskite Films for Efficient Light-Emitting Diodes.

Despite the recent advances in the performance of perovskite light-emitting diodes (PeLEDs), the effects of water on the perovskite emissive layer and its electroluminescence are still unclear, even though it has been previously demonstrated that moisture has a significant impact on the quality of perovskite films in the fabrication process of perovskite solar cells and is a prerequisite for obtaining high-performance PeLEDs. Here, the effects of postmoisture on the luminescent CH3 NH3 PbBr3 (MAPbBr3 ) perovskite films are systematically investigated. It is found that postmoisture treatment can efficiently control the morphology and growth of perovskite films and only a fast moisture exposure at a 60% high relative humidity results in significantly improved crystallinity, carrier lifetime, and photoluminescence quantum yield of perovskite films. With the optimized moisture-treated perovskite films, a high-performance PeLED is fabricated, exhibiting a maximum current efficiency of 20.4 cd A-1 , which is an almost 20-fold enhancement when compared with perovskite films without moisture treatment. The results provide valuable insights into the moisture-assisted growth of luminescent perovskite films and will aid in the development of high-performance perovskite light-emitting devices.

Modified Conducting Polymer Hole Injection Layer for High-Efficiency Perovskite Light-Emitting Devices: Enhanced Hole Injection and Reduced Luminescence Quenching.

Modification of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) with sodium-poly(styrenesulfonate) leads to a ca. 0.3 eV increase in the work function and 15 times enhancement in the photoluminescence intensity of the overlying perovskite layer, which is closely correlated with the formation of a highly PSS-enriched top layer. As a direct result, the hybrid halide perovskite light-emitting devices with a modified PEDOT:PSS layer show the maximum external quantum efficiency of 7.2% and power efficiency of 19.0 lm W-1, which are 14-20 times those of the analogous devices using a pristine PEDOT:PSS layer and among the best reported values for the light-emitting devices using a neat perovskite emission layer. Our results illustrate that insufficient hole injection and luminescence quenching at the PEDOT:PSS anode are among the most important factors limiting the external quantum efficiencies of inverted perovskite light-emitting devices.