Perovskite Quantum Dot Light-emitting Diodes Research Articles

Acid‐etching induced metal cation competitive lattice occupancy of perovskite quantum dots for efficient pure‐blue QLEDs

AbstractLow efficiency and spectral instability caused by the surface defects have been considerable issues for the mixed‐halogen blue emitting perovskite quantum dots light‐emitting diodes (PeQLEDs). Here, an in situ surface passivation to perovskite quantum dots (PeQDs) is realized by introducing the metal cations competitive lattice occupancy assisted with acid‐etching, in which the long‐chain, insulating and weakly bond surface ligands are removed by addition of octanoic acid (OTAC). Meanwhile, the dissolved A‐site cations (Na+) compete with the protonated oleyl amine and are subsequently anchored to the surface vacancies. The preadded lead bromide, acting as inorganic ligands, demonstrates strong bonding to the uncoordinated surface ions. The as‐synthesized PeQDs show the boosted photoluminescence quantum yield (PLQY) and superior stability with longer lifetime. As a result, the PeQLEDs (470 nm) based on the OTAC‐Na PeQDs exhibit an external quantum efficiency of 8.42% in the mixed halogen PeQDs (CsPb(BrxCl1−x)3). Moreover, the device exhibits superior spectra stability with negligible shift. Our competition mechanism in combination with in situ passivation strategy paves a new way for improving the performance of blue PeQLEDs.

High‐Efficiency Pure Red CsPbI3 QLEDs Via Strong Electron Affinity Interface Layer Engineering

AbstractInorganic perovskite quantum dots (QDs) have garnered significant attention due to their outstanding optical properties. However, perovskite quantum dot light‐emitting diodes (Pe‐QLEDs) still face challenges related to their fluorescence efficiency and electron injection. First, the electron transport layer (ETL) leads to severe non‐radiative recombination due to fluorescence quenching in CsPbI3 QDs. Second, there is an electron injection imbalance resulting from low electron injection efficiency, leading to reduced non‐radiative recombination and external quantum efficiency. To address these issues, this study introduces two interface layer materials with different electron affinities, 1,3,5‐Tris(3‐pyridyl‐3‐phenyl)benzene (TmPyPB) and 2,4,6‐Tris(3′‐(pyridine‐3‐yl)biphenyl‐3‐yl)‐1,3,5‐triazine (TmPPPyTz). These materials not only passivated defects on the surface of CsPbI3 QDs films but also effectively prevented the fluorescence quenching of CsPbI3 QDs by the PO‐T2T (ETL). TmPPPyTz, with a relatively lower LUMO energy level, further improved energy level matching, significantly enhancing electron injection efficiency. Ultimately, using interface engineering with the TmPPPyTz interface layer, the devices achieved an outstanding 25.80% champion‐level external quantum efficiency (EQE) for Pe‐QLEDs with only a sub‐bandgap voltage of 1.7 V and half‐life (T50) is 17.99 h at 100 nits. This research provided an effective method to enhance the performance of CsPbI3 Pe‐QLEDs, addressing long‐standing issues inhibiting their efficiency.

Co-regulation strategy dominated by double short molecules permitting the regrowth of quantum dots for efficient deep-blue perovskite light-emitting diodes

Recently, blue perovskite quantum dots (PeQDs) have garnered considerable attention for use in full-color optoelectronic displays. However, the large specific surface area caused by the small particle size of blue PeQDs results in high defect state density, which severely limits their optical pursuit. To address this issue, a co-regulation strategy using double short-chain molecules of tetraoctylammonium fluoride and tetraethylammonium perfluorooctanesulfonate is proposed to enhance the regrowth of blue CsxRb1−xPb(ClyBr1−y)3 PeQDs. Long-chain insulated oleylamine and oleic acid ligands, which restrict the growth of PeQDs, are substantially replaced using short-chain ligands with higher adsorption energy. This replacement promotes PeQDs to regrow considerably from ∼8 to ∼18 nm, and the defect-state density decreases by 3–5 times. Consequently, highly efficient blue PeQDs with a photoluminescent quantum yield of unity are obtained. Moreover, the PeQDs exhibit lower insulating ligand density and improved charge injection property. As a result, the synthesized deep-blue PeQD light-emitting diodes (PeQLEDs) exhibit a maximum external quantum efficiency of 5.7% at the CIE coordinate of (0.148, 0.032). According to the International Telecommunication Union Radiocommunication Sector television standard (Rec. 2100), the obtained PeQLEDs are state-of-the-art among colloidal deep-blue PeQDs. This study provides a novel strategy to improve the optical performance of deep-blue PeQLEDs and paves the way for developing high-end wide color-gamut displays.

Bulky Passivation by an Electroactive Phosphonate Dendrimer for High-Performance Perovskite Quantum Dot Light-Emitting Diodes

Bulky Passivation by an Electroactive Phosphonate Dendrimer for High-Performance Perovskite Quantum Dot Light-Emitting Diodes

Sulfonate Additive Simultaneously Suppresses Interstitials and Vacancies Toward Efficient and Stable Perovskite Quantum Dot LEDs

AbstractDefect suppression via precursor additives is crucial to achieving high efficiency and stable perovskite quantum dot light‐emitting diodes (Pe‐QLEDs). Herein, a strategy using 4‐dodecylbenzenesulfonic acid (DBSA) is developed to simultaneously suppress halide interstitial and vacancy defects by tuning the crystallization process of perovskite quantum dots (Pe‐QDs) through coordinate bonding and chemical circumstance modulation, leading to faster radiative recombination and less carrier accumulation in the device. Meanwhile, the Pe‐QDs with defect suppression demonstrate higher ion migration activation energies. Thanks to the defect suppression strategy with the aid of the alkyl sulfonic group, the obtained Pe‐QDs exhibit an external quantum efficiency (EQE) of up to 20.4% and an operating lifetime of over 100 h in QLED, which is the leading performance of green Pe‐QLEDs. This work provides a strategy from a different aspect for the perovskite QLED field in improving the performance and stability of devices.

Preparation and performance optimization of bromine-based perovskite quantum dot light-emitting diodes

Preparation and performance optimization of bromine-based perovskite quantum dot light-emitting diodes

Bilayer phosphine oxide modification toward efficient and large-area pure-blue perovskite quantum dot light-emitting diodes

Blue emissive halide perovskite light-emitting diodes (LEDs) are gaining increasing attention. Reducing defects in halide perovskites to improve the performance of the resulting LEDs is a main research direction, but there are limited passivation methods for achieving efficient and spectrally-stable pure-blue LEDs based on mixed-halide perovskites. In this work, double modification layers containing phosphine oxides, i.e., diphenyl[4-(triphenylsilyl)phenyl]phosphine oxide (TSPO1) and 2,7-bis(diphenylphosphoryl)-9,9′-spirobifluorene (SPPO13), are developed to passivate mixed-halide perovskite quantum dot (QD) films. The comprehensive spectroscopic and structural characterization results indicate the presence of strong interactions between TSPO1/SPPO13 and the QDs. Besides, the combination of the bilayer exhibits a synergistic hole-blocking effect, improving the charge balance of the LEDs. LEDs based on the QD/TSPO1/SPPO13 films deliver stable electroluminesence at 469 nm and present a maximum external quantum efficiency (EQE) and luminance of 4.87% and 560 cd m−2, respectively. Benefiting from the uniform QD/TSPO1/SPPO13 film over a large area, LEDs with an area of 64 mm2 show a maximum EQE of 3.91%, which represents the first efficient large-area mixed-halide perovskite LED with stable pure-blue emission. This work provides a method to improve the perovskite QDs-based film quality and optoelectronic properties, and is a step toward the fabrication of highly-efficient large-area blue perovskite LEDs.

Highly Solvent Resistant Small-Molecule Hole-Transporting Materials for Efficient Perovskite Quantum Dot Light-Emitting Diodes.

Perovskite quantum dot light-emitting diodes (Pe-QLEDs) have been shown as promising candidates for next-generation displays and lightings due to their unique feature of wide color gamut and high color saturation. Hole-transporting materials (HTMs) play crucial roles in the device performance and stability of Pe-QLEDs. However, small-molecule HTMs have been less studied in Pe-QLEDs due to their poor solvent resistance and low hole mobility. In this work, three novel small-molecule HTMs employing benzimidazole as the center core, named X4, X5, and X6, were designed and synthesized for application in Pe-QLEDs. One of the tailored HTM-X6 exhibits excellent solvent resistant ability to the perovskite quantum dot (QD) inks due to its proper solubility and low surface energy. Our result clearly demonstrated that the synergistic effect of poor solubility and low surface energy facilitates the achievement of good solvent resistance to perovskite QD inks. As a result, a promising maximal external quantum efficiency (EQE) of 14.1% is achieved in X6-based CsPbBr3 Pe-QLEDs, which is much higher than that of X4 (9.16%) and X5 (6.60%)-based devices, which is comparable to the PTAA reference (EQE ∼ 15.8%) under the same conditions. To the best of our knowledge, this is the first example that a benzimidazole-based small-molecule HTM demonstrated a good application in Pe-QLEDs. Our work provides new guidance for the rational design of small-molecule HTMs with high solvent resistance for efficient Pe-QLEDs and other photoelectronic devices.

Interface-Induced Crystallinity Enhancement of Perovskite Quantum Dots for Highly Efficient Light-Emitting Diodes.

Perovskite quantum dot light-emitting diodes (QLEDs) with high color purity and wide color gamut have good application prospects in the next generation of display technology. However, colloidal perovskite quantum dots (PQDs) may introduce a large number of defects during the film-forming process, which is not conducive to the luminous efficiency of the device. Meanwhile, the disordered film formation of PQDs will form interfacial defects and reduce the device performance. Here, we report an interface-induced crystallinity enhancement (IICE) strategy to increase the crystallinity of PQDs at the hole transport layer (HTL)/PQD interface. As a result, both the Br- vacancies in the PQD film and the interfacial defects were well passivated and the leakage current was also suppressed. We achieved QLEDs with a maximum external quantum efficiency (EQE) of 16.45% and current efficiency (CE) of 61.77 cd/A, showing improved performance to more than twice that of the control devices. The IICE strategy paves a new way to enhance the crystallinity of PQD films, so as to improve the performance of QLEDs for application in the future display field.

Surface Passivation with Selected Phosphine Oxide Molecules for Efficient Pure‐Blue Mixed‐Halide Perovskite Quantum Dot Light‐Emitting Diodes

AbstractPassivation of defects in halide perovskite using phosphine oxide or alkyl‐phosphonate has recently obtained a few remarkable achievements. However, effective application of phosphine oxide or alky‐phosphonate in passivating perovskite quantum dots (QDs) are seldom reported due to solubility issue or difficulty of amount control. In this work, two bifunctional organic molecules containing phosphine oxide groups, 2,4,6‐Tris[3‐(diphenylphosphinyl)phenyl]‐1,3,5‐triazine (PO‐T2T) and 2,7‐bis(diphenylphosphoryl)‐9,9′‐spirobifluorene (SPPO13), are deposited on QDs films by thermal evaporation. The molecules, both as passivation agents as well as electron transporting materials, exhibit stark contrast in passivating QDs and in light‐emitting diodes (LEDs) performance. A competition between charge transfer and defect passivation between the QDs and the molecules is proposed. In film, electron transfer from the QDs to PO‐T2T dominates and quench the QDs, while the passivation effect of PO‐T2T on the QDs dominates in driving device and enhances luminance of the LEDs. In contrast, passivation effect of SPPO13 on the QDs dominates both in films and in LEDs. A maximum EQE of 2.67% is obtained for the pure‐blue LED based on SPPO13‐passivated QDs films. This work provides a guide on the selection of passivation agents based on phosphine oxide and a promising passivation method for high‐efficient perovskite QD LEDs.

Improving Perovskite Green Quantum Dot Light-Emitting Diode Performance by Hole Interface Buffer Layers.

Perovskite quantum dot light-emitting diodes (QLEDs) are potential candidates for next-generation displays due to their high color purity and wide color gamut. Due to the strong electron-accepting ability of poly[bis(4-phenyl) (2,4,6-trimethylphenyl) amine] (PTAA), quantum dot (QD) films are prone to be charged, which leads to the imbalance of charge injection and the increase of nonradiative recombination, ultimately affecting the performance of the QLEDs. Here, we compared and studied two polymers, poly(methyl methacrylate) (PMMA) and poly(vinyl pyrrolidone) (PVP), as the hole interface buffer layers of QD films, which effectively reduced the defect density, suppressed nonradiative recombination, and greatly improved the efficiency and stability of QLEDs. The devices with PMMA achieved a maximum external quantum efficiency of 20.71%.

A Multifunctional Small-Molecule Hole-Transporting Material Enables Perovskite QLEDs with EQE Exceeding 20%

Hole-transporting materials (HTMs) play critical roles in the device performance and stability of perovskite quantum dot light-emitting diodes (Pe-QLEDs). However, the development of small-molecule HTMs for achieving high-performance Pe-QLEDs has proven to be very challenging because of their low hole mobility and poor solvent resistance. Herein, we tailor-made a multifunctional small-molecule HTM, termed X10, with methoxy as the substituents, for application in Pe-QLEDs. X10 features high hole mobility, good film-forming ability, and strong solvent resistance ability as well as defect passivation effect. Subsequently, Pe-QLEDs employing X10 as HTM presented a promising external quantum efficiency (EQE) of 20.18%, which is 7-fold higher than that of the reference HTM-TCTA-based ones (EQE ≈ 2.88%). To the best of our knowledge, this is the first case in which a small-molecule HTM displays a high EQE over 20% in Pe-QLEDs. Our work provides important guidance for the rational design of multifunctional small-molecule HTMs for high-performance Pe-QLEDs.

Balancing Charge Injection via a Tailor-Made Electron-Transporting Material for High Performance Blue Perovskite QLEDs

One of the great challenges in perovskite quantum dot light-emitting diodes (Pe-QLEDs) is the unbalanced charge injection that significantly hinders the device performance and stability. Herein, we tailor-made a high mobility electron-transporting material (ETM), named B2, to balance the carrier injection in blue Pe-QLEDs. B2 with a tailored asymmetric anthracenyl structure exhibits a promising electron mobility of 2.7 × 10–4 cm2·V–1·s–1, which is almost 20 times higher than the commonly used ETM-TPBi (1.1 × 10–5 cm2·V–1·s–1). Subsequently, sky blue (490 nm) Pe-QLED with B2 as the ETM presented a remarkably high external quantum efficiency (EQE) of 13.17% and a low turn-on voltage of 2.2 V, which is much better than that of the TPBi-based device (EQE of 8.31% and Vturn-on of 3.2 V). In addition, B2 also demonstrated a universal application in green and deep blue Pe-QLEDs. This work provides an important guidance to rational design of high electron mobility ETMs for high-performance LEDs.

Spiro-based hole-transporting materials utilized in green perovskite quantum dot light-emitting diodes with high luminance

Pe-QLEDs based on two spiro-cored HTMs achieved high brightness of 45 056 and 46 382 cd m−2, respectively.

High efficiency pure blue perovskite quantum dot light-emitting diodes based on formamidinium manipulating carrier dynamics and electron state filling

Achieving high efficiency and stable pure blue colloidal perovskite quantum dot (QD) light-emitting diodes (LEDs) is still an enormous challenge because blue emitters typically exhibit high defect density, low photoluminescence quantum yield (PLQY) and easy phase dissociation. Herein, an organic cation composition modification strategy is used to synthesize high-performance pure blue perovskite quantum dots at room temperature. The synthesized FA-CsPb(Cl0.5Br0.5)3 QDs show a bright photoluminescence with a high PLQY (65%), which is 6 times higher than the undoped samples. In addition, the photophysical properties of the FA cation doping was deeply illustrated through carrier dynamics and first principal calculation, which show lower defects, longer lifetime, and more reasonable band gap structure than undoped emitters. Consequently, pure blue FA-CsPb(Cl0.5Br0.5)3 QDs light-emitting devices were fabricated and presented a maximum luminance of 1452 cd m−2, and an external quantum efficiency of 5.01 % with an emission at 474 nm. The excellent photoelectric properties mainly originate from the enhanced blue QDs emitter and effective charge injection and exciton radiation. Our finding underscores this easy and feasible room temperature doping approach as an alternative strategy to blue perovskite QD LED development.

Electron donor–acceptor (D-A) tuning to achieve soluble covalent organic polymers for optoelectronic devices

Covalent organic polymers (COPs) have emerged as a unique class of luminescent polymers with pre-designed quasi-ordered architectures. However, their layered stacks and limited solubility preclude further processing for large-scale applications in devices, especially optoelectronic equipment. Herein, a universal strategy to adjust the electron donor–acceptor (D-A) moieties of the building blocks in COPs is proposed, achieved by in situ charge exfoliation of COP blocks into few-layer true solutions in (Lewis) acid and base media. The electron D-A moieties of the building blocks endow the COPs with the ability to accept or donate electrons, by altering the electron cloud distribution as well as the relative energy levels of the frontier molecular orbitals. The resultant soluble COPs can easily be processed into a uniform film by solution processing via the spin-coat method. The obtained COP-N achieves efficient and stable perovskite electroluminescence as a novel hole injection material on indium tin oxide, and the operating lifetime for a perovskite quantum dot light-emitting diodes device exceeds that of a poly(ethylene dioxythiophene):polystyrene sulphonate counterpart. This straightforward electronic regulation strategy provides a new avenue for the rational synthesis of processable reticular molecular polymers for practical electronic devices.

Enriched-Bromine Surface State for Stable Sky-Blue Spectrum Perovskite QLEDs With an EQE of 14.6.

Halogen vacancies are of great concern in blue-emitting perovskite quantum-dot light-emitting diodes because they affect their efficiency and spectral shift. Here, an enriched-bromine surface state is realized using a facile strategy that employs a PbBr2 stock solution for anion exchange based on Cd-doped perovskite quantum dots. It is found that the doped Cd ions are expected to reduce the formation energy of halogen vacancies filled by the external bromine ions, and the excess free bromine ions in solution are enriched in the surface by anchoring with halogen vacancies as sites, accompanied with the shedding of surface long-chain ligands during the anion exchange process, resulting in a Br-rich and "neat" surface. Moreover, the surface state exhibits good passivation of the surface defects of the controlled perovskite QDs and simultaneously increases the exciton binding energy, leading to excellent optical properties and stability. Finally, the sky-blue emitting perovskite quantum-dot light-emitting diodes (QLEDs) (490nm) are conducted with a record external quantum efficiency of 14.6% and current efficiency of 19.9cd A-1 . Meanwhile, the electroluminescence spectra exhibit great stability with negligible shifts under a constant operating voltage from 3 to 7V. This strategy paves the way for improving the efficiency and stability of perovskite QLEDs.

Perovskite Quantum Dots for Emerging Displays: Recent Progress and Perspectives.

The excellent luminescence properties of perovskite quantum dots (PQDs), including wide excitation wavelength range, adjustable emission wavelength, narrow full width at half maximum (FWHM), and high photoluminescence quantum yield (PLQY), highly match the application requirements in emerging displays. Starting from the fundamental structure and the related optical properties, this paper first introduces the existing synthesis approaches of PQDs that have been and will potentially be used for display devices, and then summarizes the stability improving approaches with high retention of PQDs’ optical performance. Based on the above, the recent research progress of PQDs in displays is further elaborated. For photoluminescent display applications, the PQDs can be embedded in the backlighting device or color filter for liquid crystal displays (LCD), or they may function as the color conversion layer for blue organic light-emitting diodes (OLED) and blue micro-scale light-emitting diodes (μLED). In terms of next-generation electroluminescent displays, notable progress in perovskite quantum-dot light emitting diodes (PeQLED) has been achieved within the past decade, especially the maximum external quantum efficiency (EQE). To conclude, the key directions for future PQD development are summarized for promising prospects and widespread applications in display fields.

Realizing full-color perovskite quantum dots light-emitting diodes via contemporary surface ligand/anion engineering

Unprecedentedly, cesium lead halide (CsPbX3, X = Cl, Br, I) quantum dots (QDs) with tunable spectral emissions and photophysical properties are used as a common emissive material for the fabrication of full-color perovskite QDs light-emitting diodes. An efficient, non-destructive ligand/anion exchange strategy is developed to fine-tune the optical properties of CsPbBr3 QDs solid-state films. Specifically, the surface of the CsPbBr3 QDs films is passivated by phenethylammonium halides, PEAX (X = Cl, Br, I) salts via a facile spin-coating technique, producing PEAX-CsPbBr3 QDs (X = Cl, Br, I) films with tunable (blue/green/red) color emissions that cover the entire visible spectrum. During passivation treatment, the PEAX passivators supply additional halide (Cl, Br, I) anions to fill in the intrinsic Br vacancies, allowing contemporary defect-passivation and emission-tuning effect in the QDs film. More importantly, this surface passivation strategy enables the fabrication of full-color perovskite QDs light-emitting diodes using PEAX-CsPbBr3 QDs as a common emissive film.

A Synergetic Codoping Strategy Enabling Performance Improvement of Pure‐Blue Perovskite Quantum Dots Light‐Emitting Diodes

AbstractHighly efficient green and red perovskite quantum dots (PeQDs) light‐emitting diodes (PeQDLEDs) have been achieved. However, blue PeQDLEDs, especially those with the relatively short wavelengths (<470 nm) meeting National Television System Committee blue standard, have struggled to match the high efficiency and stability of their red and green counterparts. The main critical problems are the low photoluminescence quantum yield (PLQY) and poor stability of PeQDs, as well as the unfavorable device structure. Herein, a strategy of codoping Mn2+ and Ni2+ in CsPb(Br1.8Cl1.2) is developed to improve the PLQY and thermal stability of PeQDs due to the defect passivation and enhanced formation energy. Meanwhile, the valence band position of PeQDs is elevated to reduce the hole injection barrier benefitting from the synergetic codoping strategy. As a result, the PeQDLEDs based on codoped PeQDs exhibit the maximum external quantum efficiency (EQE) of 3.31% with the emission peak located at 469 nm, and lifetime exceeding 8 min. The work provides a new avenue to achieve efficient and stable pure blue PeQDLEDs.