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Limited stability of blue quantum dot light-emitting diodes (QLEDs) under current stress impedes commercialization. Multi-layer structures of the state-of-the-art blue QLEDs pose significant difficulty in the fundamental understanding of degradation mechanisms. Here, by applying transient electroluminescence measurements, we disentangle charge transport in both pristine and degraded blue QLEDs. By varying thicknesses of the charge transport layers and the emissive layer, respectively, we show that the charge transport in pristine QLEDs is primarily dominated by holes. Furthermore, the degradation of QLEDs under electrical stress is governed by the decrease of hole transport in the emissive quantum dot layer due to the formation of hole traps. [ABSTRACT FROM AUTHOR]

The characteristic voltages in the capacitance–voltage (C–V) curve of quantum dot light-emitting diodes (QLEDs) are usually linked to the start of charge injection and recombination in a working device. However, it may lead to a misunderstanding of the carrier process in QLEDs. This is because capacitance change only reflects an electrical response of additional carriers induced by a small signal loaded on an applied DC voltage but does not directly correlate with the total free carrier response governed by the working voltage. In this work, we study the frequency-dependent C–V characteristics of a blue QLED, focusing on the characteristic voltages, characteristic times, and their relationships. First of all, we identify that the charge injection point of QLEDs should be extracted by the current density–voltage–luminance characteristics rather than the C–V curve. As for the characteristic voltages obtained from the C–V curve, they are determined by voltage-dependent characteristic times in different time domains. Furthermore, the C–V characteristic is helpful to evaluate charge accumulation or leakage in blue QLED, serving as an accessible analysis tool in the carrier transport process. Our work provides a definite physical meaning of characteristic voltages in the C–V curve and exhibits the usefulness of C–V characteristics for analyzing the charge dynamics of QLED. [ABSTRACT FROM AUTHOR]

Core–shell structural ZnSeTe/ZnSe/ZnS quantum dots (QDs) have attracted great attention for advanced illumination and displays because of their environmentally friendly composition, but still suffering from poor photoluminescence (PL) and electroluminescence (EL) performance due to severe non‐radiative charge recombination. Herein, a stepwise injection shell growth process to manipulate the monomer concentration and ensure adequate growth interval is devised, which enables the controllable uniform epitaxial growth of ZnSe and ZnS shells on the ZnSeTe core, thus relieving the lattice distortion and defects to greatly suppress the non‐radiative charge recombination. The ZnSeTe/ZnSe/ZnS QDs presented deep‐blue emission at 448 nm with narrow full width at half maximum (FWHM, 23 nm), and near‐unity PL quantum yield (PLQY, ≈100%) The light‐emitting diodes (LEDs) based on the QDs exhibited a high external quantum efficiency (EQE) of 10.9%, a maximum brightness of 10240 cd cm−2, and a high current efficiency of 7.9 cd A−1, demonstrating a good performance for deep blue QDs LEDs (QLEDs) This shell growth strategy will be an effective approach to achieving efficient QDs and QLEDs. [ABSTRACT FROM AUTHOR]

Blue light‐emitting CdSe@ZnS/ZnS quantum dot (QD) nanoparticles (NPs) were synthesized and their photophysical properties in both solution and film phases were investigated. The morphological properties of films prepared by different coating methods i. e. single layer coating from low to high concentrations of QD solutions and layer‐by‐layer (multilayer) coating within constant low QD solution concentration, were also examined in detail. Varying the concentration (1–10 mg/mL) and the number of layers (from 1–16) did not essentially affect the photophysical properties of QD films, although it resulted in a direct increment in QD film thickness. The concentration and layer‐dependent films were used as an emissive layer (EML) in QD light‐emitting diodes (QLEDs). Although the "6 mg/ml−1 Layer" QD EML‐based device exhibited relatively high device efficiency compared to the "1 mg/ml−10 Layers" based one at working voltage region, it had ~2‐fold higher efficiency roll‐off at high voltage region. The performance differences for both devices with the same QD EML thickness were attributed to the morphological variations for the QD layer in terms of surface roughness, void density, aggregates/clusters, and trap sites that were directly related to the charge injection balance and Auger recombination. [ABSTRACT FROM AUTHOR]

As the demand of outdoor displays grows, light-emitting diodes characterized by multifunction with water resistance, anti-reflection, and self-cleaning have gradually become an important and active research area. Herein, the rose petal epidermal microstructures have been employed as inspiration in flexible semitransparent encapsulation for quantum dot light-emitting diodes (QLEDs). This bio-inspired encapsulation not only effectively blocks the water and oxygen, but is easily self-cleaned by removing the physically adhered dusts because of its superhydrophobic surface. Moreover, the rose petal-inspired encapsulation also possesses strong anti-reflection ability for visible light due to its microstructure engraved on the surface. As a result, the semitransparent QLEDs with the rose petal-inspired encapsulation show a high brightness of 28637 cd/m2 as well as excellent self-cleaning and anti-reflection capacities. Thus, this work offers an effective encapsulation strategy for QLEDs and also other flat-panel light-emitting diodes to adapt to outdoor applications via utilizing biological microstructures. [ABSTRACT FROM AUTHOR]

At present, heavy-metal-free quantum dot light-emitting diodes (QLEDs) have shown great potential as a research hotspot in the field of optoelectronic devices. This article reviews the research on heavy-metal-free quantum dot (QD) materials and light-emitting diode (LED) devices. In the first section, we discussed the hazards of heavy-metal-containing quantum dots (QDs), such as environmental pollution and human health risks. Next, the main representatives of heavy-metal-free QDs were introduced, such as InP, ZnE (E=S, Se and Te), CuInS2, Ag2S, and so on. In the next section, we discussed the synthesis methods of heavy-metal-free QDs, including the hot injection (HI) method, the heat up (HU) method, the cation exchange (CE) method, the successful ionic layer adsorption and reaction (SILAR) method, and so on. Finally, important progress in the development of heavy-metal-free QLEDs was summarized in three aspects (QD emitter layer, hole transport layer, and electron transport layer). [ABSTRACT FROM AUTHOR]

Breaking the theoretical limits of external quantum efficiency (EQE) and obtaining quantum dot light‐emitting diodes (QLEDs) with high brightness, high efficiency, and low operating voltage is the basis of commercial applications in display and illumination. Devices with an EQE of over 20% can be realized by carrier equilibrium injection and light out‐coupling enhancement. However, it is difficult to synergistically enhance the performance of QLEDs by combining the light out‐coupling and the hole enhancement injection. In this paper, the injection enhancement of holes and the light out‐coupling are realized simultaneously only by nano‐imprint lithography (NIL). The π─π bonds of the PEDOT: PSS film treated by NIL demonstrate a molecular orientation perpendicular to the substrate, which improves the injection of the hole. The PEDOT: PSS patterned by NIL further presents improved light out‐coupling. Consequently, the EQE of red‐QLED is 30.42% with a synergistic enhancement factor of 61%, accompanying the maximum brightness increased by 8% to 125 200 cd m−2 at 4.6 V (Vturn‐on, 1.74 V). The EQE and brightness of green‐QLED increased by 38.9% and 34.3% to 24.16% and 279 700 cd m−2, respectively. Therefore, NIL will provide new insights into synergistically enhancing light out‐coupling and internal quantum efficiency to break through the performance of electroluminescence (EL). [ABSTRACT FROM AUTHOR]

Inorganic 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. [ABSTRACT FROM AUTHOR]

Owing to the excellent optoelectronic properties of colloidal quantum dots (QDs), light‐emitting diodes based on QDs (QLEDs) have been considered one of the most promising electroluminescence (EL) devices for full‐color displays with a wide color gamut. Particularly, top‐emission device architecture has been of interest to both academia and industry, because of the advantages in light outcoupling, aperture ratios, and integration with conventional backplanes. In this structure, however, angle‐dependent color shifts originating from a variation in microcavity length are a critical issue that needs to be resolved. Here, a solution‐processed dual‐functional scattering–capping layer (SCPL) using ZnO nanoparticles on top‐emitting QLEDs with ZnSeTe/ZnSe/ZnS QDs to modulate the optical interference is presented. By precisely controlling the thickness of the SCPL, the EL intensity and spectrum can be redistributed to produce a uniform color from any viewing angle. It is discovered that, unlike conventional CPLs, the formation of random nanocracks and nanoclusters in the SCPL adds subwavelength light‐scattering capabilities, which promotes light extraction. The QLEDs with the solution‐processed SCPL exhibit a 44% increase in the maximum external quantum efficiency, with completely imperceptible angle‐dependent spectral shifts. The SCPL is expected to be applied to the development of high‐performance and next‐generation QLED displays. [ABSTRACT FROM AUTHOR]

[Display omitted] Poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) has been widely used as a hole injection material in quantum dot (QD) light-emitting diodes (QLEDs). However, it degrades the organic materials and electrodes in QLEDs due to its strong hydroscopicity and acidity. Although hole-conductive metal oxides have a great potential to solve this disadvantage, it is still a challenge to achieve efficient and stable QLEDs by using these solution-processed metal oxides. Herein, the state-of-the-art QLEDs fabricated by using hole-conductive MoO x QDs are achieved. The α-phase MoO x QDs exhibit a monodispersed size distribution with clear and regular crystal lattices, corresponding to high-quality nanocrystals. Meanwhile, the MoO x film owns an excellent transmittance, suitable valence band, good morphology and impressive hole-conductivity, demonstrating that the MoO x film could be used as a hole injection layer in QLEDs. Moreover, the rigid and flexible red QLEDs made by MoO x exhibit peak external quantum efficiencies of over 20%, representing a new record for the hole-conductive metal oxide based QLEDs. Most importantly, the MoO x QDs afford their QLEDs with a longer T 95 lifetime than these devices made by PEDOT:PSS. As a result, we believe that the MoO x QDs could be used as efficient and stable hole injection materials used in QLEDs. [ABSTRACT FROM AUTHOR]

Defect 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. [ABSTRACT FROM AUTHOR]

Quantum dot light-emitting diodes (QLEDs), as an emerging display technology, have garnered widespread attention due to their excellent color rendering, high efficiency, and long lifespan. However, the inherent differences in the properties of charge transport layer materials inevitably lead to charge injection imbalances and low device performance. Herein, we developed a simple technique by using femtosecond laser scanning over the QLED devices. The results indicate that scanning with a femtosecond laser improves the conductivity of the hole transport layer and increases the external quantum efficiency of the QLED devices. Our work provides an effective route for realizing high performance QLED devices with efficient post-treatment. [ABSTRACT FROM AUTHOR]

The superior optical properties of colloidal quantum dots (QDs) have garnered significant broad interest from academia and industry owing to their successful application in self‐emitting QD‐based light‐emitting diodes (QLEDs). In particular, active research is being conducted on QLEDs with top‐emission device architectures (TQLEDs) owing to their advantages such as easy integration with conventional backplanes, high color purity, and excellent light extraction. However, due to the complicated optical phenomena and their highly sensitive optoelectrical properties to experimental variations, TQLEDs cannot be optimized easily for practical use. This review summarizes previous studies that have investigated top‐emitting device structures and discusses ways to advance the performance of TQLEDs. First, theories relevant to the optoelectrical properties of TQLEDs are introduced. Second, advancements in device optimization are presented, where the underlying theories for each are considered. Finally, multilateral strategies for TQLEDs to enable their wider application to advanced industries are discussed. This work believes that this review can provide valuable insights for realizing commercial TQLEDs applicable to a broad range of applications. [ABSTRACT FROM AUTHOR]

Micro‐patterning silver nanowires (AgNWs) via solution processes is vital in making high‐performance transparent flexible electrodes (TFE) that have been widely used in optoelectronic devices. However, it has suffered from the limitation of a trade‐off relationship between the coverage and the arrangement of AgNWs, which determine the transparency and the conductivity, respectively. Here, unique AgNWs micro‐patterns, featuring as the crossing‐grid of high‐resolution and highly‐aligned AgNWs micro‐lines, which enable the micro‐pattern highly cross‐aligned with a limited 3.9% coverage, are developed. Consequently, a TFE with an ultra‐high transmittance over 98.5% and a sheet resistance of 25.5 Ω sq−1 is developed. Guided by the unit of triple conical fibers, AgNWs are controllable transferred onto the target area, leaving a line with a width‐resolution up to 2 µm. Simultaneously, AgNWs are aligned under the synergistic effect of both the solution‐shearing and the tri‐phase contact line confinement. Using the as‐developed TFE as either the top or the bottom electrode, a transparent quantum dot light‐emitting diode (T‐QLED) with a transmittance of 89.8%, as well as a flexible T‐QLED with a transmittance of 92.8% are demonstrated, much higher than those of T‐QLEDs reported. It is envisioned that the result would inspire the fabrication of high‐performance transparent optoelectronic devices. [ABSTRACT FROM AUTHOR]

Although significant progress has been made in improving the external quantum efficiencies (EQEs) of perovskite quantum dot (QD) light‐emitting diodes (QLEDs), understanding the degradation mechanism and enhancing stability remain a challenge. Herein, increasing the content of Br‐based passivation ligands is shown to enhance the EQE up to 16.1% by reducing the defects of CsPbBr3 QDs in a Br‐rich environment. However, the operational lifetimes of perovskite QLEDs gradually decrease with the increase of halide content, owing to the intensified ion migration under continuous electric field confirmed by the current behavior of QLEDs and time‐of‐flight secondary‐ion mass spectrometry. Furthermore, a thorough analysis of the relationship between electricity and luminance of QLEDs suggests that a small amount of residue oleic acid ligands could weaken ion migration. Accordingly, a halide‐ and acid‐hybrid (HAH) co‐passivation strategy is proposed to optimize the content of Br‐ and acid‐based ligands, and achieve a maximum EQE of 18.6% and an operational lifetime (T50, extrapolated) of 213 h for CsPbBr3 QLEDs. This approach for passivating QDs combines the high efficiency of Br‐based ligands with the improved stability of acid‐based ligands. The study elucidates the correlation between ligands and device performance, highlighting the significance of two or even multiple ligands for efficient and stable perovskite QLEDs. [ABSTRACT FROM AUTHOR]

Currently, the performance of quantum‐dot light‐emitting diodes (QLEDs) based on environmental‐friendly Cu─In─Zn─S quantum dots (QDs) still lags far behind that of Cd‐QDs‐based devices. Here it is demonstrated that the unique trap‐related recombination in Cu─In─Zn─S QDs is mainly responsible for the low device efficiency. The luminous efficiency of Cu─In─Zn─S‐based QLEDs is rather sensitive to the temperature and hole‐transporting layers (HTLs) due to the susceptible thermal‐related trappingdetrapping processes of holes in radiative Cu‐related traps. The holes in Cu‐related traps can be quenched by escaping to the valence band of the QDs or/and transferring to the adjacent HTLs. An HTL with low highest occupied molecular orbitals is desired to enhance the hole injection and hinder the aforementioned hole transfer. As a result, a high device efficiency of 6.0 cd A−1 is achieved at room temperature, which is attributed to suppressed HTL‐induced emission quenching and efficient valence‐band‐dominated hole injection from HTL to the QDs. The device efficiency is further increased to 13.2 cd A−1 at 150K by suppressing thermal‐induced quenching. [ABSTRACT FROM AUTHOR]

[Display omitted] In terms of tunable luminescence and high quantum efficiency, colloidal quantum dots (CQDs) are promising semiconductors for constructing near-infrared light-emitting diodes (NIR-LEDs). However, currently available NIR-LEDs are susceptible to variations in the emission layer thickness (EMLT), the highest external quantum efficiency (EQE) decreases to below 50% (relative to peak EQE) when the EMLT varies out of a narrow range of (±30 nm). This is due to the thickness-dependent carrier recombination rate and current density variation, resulting in batch-to-batch EQE fluctuations that limit LED reproducibility. Here we report efficient NIR-LEDs that exhibit EQE variations of less than 15% (relative to the champion EQE) over an EMLT range of 40–220 nm; the highest achievable EQE of ∼11.5% was obtained by encapsulating a 212 nm-thick CQD within a type-I inorganic shell to enhance the radiative recombination in the dots, resulting in a high photoluminescence quantum yield of 80%, and by post-treating the films with a bifunctional linking agent to improve and balance the hole and electron mobilities in the entire film (electron mobility: 8.23 × 10−3 cm2 V−1 s−1; hole mobility: 7.0 × 10−3 cm2 V−1 s−1). This work presents the first NIR-LEDs that exhibit EMLT-invariant EQE over an EMLT range of 40–220 nm, which represents the highest EQE among reported CQD NIR-LEDs with a QD thickness exceeding 100 nm. [ABSTRACT FROM AUTHOR]

The aerobic and thermal stability of quantum-dot light-emitting diodes (QLEDs) is an important factor for the practical applications of these devices under harsh environmental conditions. We demonstrate all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of > 14% with almost negligible efficiency roll-off (droop) and a peak brightness of > 600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air conditions. We investigate the device efficiency and brightness level at a temperature range between − 10 and 85 °C in a 5-step cooling/heating cycle. We conducted the experiments at brightness levels higher than 10,000 cd/m2, required for outdoor lighting applications. Our device performance proves thermal stability, with minimal standard deviation in the performance parameters. Interestingly, the device efficiency parameters recover to the initial values upon returning to room temperature. The variations in the performance are correlated with the modification of charge transport characteristics and induced radiative/non-radiative exciton relaxation dynamics at different temperatures. Being complementary to previous studies on the subject, the present work is expected to shed light on the potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs and encourage further research for solid-state lighting applications. [ABSTRACT FROM AUTHOR]

Organic–inorganic hybrid perovskite quantum dots (QIHP‐QDs) have aroused widespread interest due to their superior photoelectric performance, quantum confinement effect, excellent photoelectric property, color‐tunability, and high photoluminescence quantum yield (PLQY) especially for QD‐based light‐emitting diodes (QLEDs). It is worth noting that a diverse selection of organic cations brings more adjustable optical properties to OIHP‐QDs compared with all‐inorganic perovskite QDs; thus the research on OIHP‐QDs has become a hit subject over recent years. This review summarizes the latest progress in synthesis strategy and optical property regulation of OIHP‐QDs in conjunction with the recent developments of their application in QLEDs. In addition, the current challenges limiting the applicability of QIHP‐QDs are discussed, and the development of OIHP‐QDs in the future is proposed. [ABSTRACT FROM AUTHOR]

We demonstrate cascaded, mid-infrared light-emitting diodes with quantum dot based active regions. Cascading is achieved through highly reverse-biased AlInAsSb tunnel junctions that serve to connect the successive InGaSb quantum dot active regions. Temperature-dependent characterization of the output irradiance as a function of the current and voltage indicates that the cascade architecture has minimal leakage currents in contrast to earlier single-stage devices and provides carrier recycling with a concomitant increase in irradiance. The results show that cascaded architectures can be applied to quantum dot platforms and that the quantum efficiency of the active region limits the overall device efficiency. [ABSTRACT FROM AUTHOR]

Recent findings show that electron transport layers (ETLs) significantly influence the electroluminescence (EL) lifetime of quantum‐dot light‐emitting diodes (QLEDs). In this work, it is found that using halide dopants in the ZnO ETL significantly enhances device EL lifetime. Electrical, photoluminescence, and photoelectron spectroscopy measurements on QLEDs and specially designed devices are used for elucidating the root causes of the lifetime enhancement. Results show that charge transfer occurs at the ZnO/QDs interface in QLEDs, producing positively charged states in ZnO, subsequently leading to luminance loss, a mechanism that contributes to EL loss. Furthermore, XPS studies show that electrical stress of QLEDs leads to an increase in the concentration of ZnO species with higher oxidative states and that a correlation between the magnitude of EL loss and the concentration of these species exists. The use of halide dopants is found to reduce this interfacial charge transfer and the formation of the ZnO species with higher oxidative states, possibly due to the dopants role in acting as hole scavengers that trap and efficiently neutralize holes in ZnO. The findings underscore the significant role that managing positive charges in ZnO plays in EL lifetime and provide an effective strategy for achieving highly stable QLED. [ABSTRACT FROM AUTHOR]

ZnMgO nanoparticles (NPs) are commonly used as the electron transport layer (ETL) in indium phosphide (InP) based quantum dots light‐emitting diodes (QLEDs). It has been experimentally found that the inherent oxygen vacancy defects in ZnMgO can be passivated by halogen additives. However, an in‐depth understanding of how the halogen additives in ZnMgO affect the quantum dots (QDs) films is currently missing. Here, the study reports on efficient and stable indium phosphide (InP) green QLEDs by effectively bridging QDs and ETL using chloride (Cl) ions. As bi‐functional anchoring additives, Cl ions not only passivate the oxygen vacancy defects of ZnMgO NPs for suppressing the exciton quenching at the QDs/ZnMgO interfaces, but also facilitate the hole transport of QDs due to part replacement of insulated oleic acid ligands on the surfaces of InP QDs with Cl anions for more balanced charge injection in the devices. Consequently, the optimized green InP QLED achieves a peak external quantum efficiency (EQE) of 13.8% and an operational lifetime of 5944 h, which, to the best of current knowledge, represents the best overall performance among the reported green InP QLEDs. [ABSTRACT FROM AUTHOR]

InP‐based quantum dots (QDs) are one of the most promising heavy‐metal‐free materials for light‐emitting applications to substitute cadmium‐analogous QDs. With a bulk band gap of 1.35 eV, InP QDs can be made to emit light in the deep red and even near‐infrared region by adjusting the size. Deep‐red light‐emitting diodes (LEDs) are of great interest for promoting the growth of plants and accurate red LED displays. However, the synthesis and the fabrication of InP‐based quantum‐dot LEDs (QLEDs) emitting in the deep red region are still under development. Here, the study reports deep‐red InP/ZnSe/ZnSeS/ZnS core‐shell QDs with a photoluminescence (PL) emission peak at 680 nm and a PL quantum yield up to 95%, which is the highest among reported deep‐red QDs. Multi‐shell with a transition layer of ZnSeS is realized to decrease the lattice mismatch in the shell and increase the shell thickness, which efficiently confines charge carriers and reduces non‐radiative recombinations. In addition, the core‐shell InP QLED achieves a high luminescence of 2263 cd m−2 and an external quantum efficiency up to 6.5%. This report provides a new strategy for promoting the development of deep‐red QLEDs for next‐generation lighting and display devices. [ABSTRACT FROM AUTHOR]

Highly efficient blue quantum‐dot light‐emitting diodes (QLEDs) are still a challenge for displays and solid‐state lighting due to light trapping in a device. Herein, an internal diffraction wrinkle pattern is used to demonstrate a spectrum‐independent enhancement strategy for light out‐coupling. The optimized device with wrinkle pattern shows a peak external quantum efficiency of 15.25% and a maximum luminance of 13 134 cd m−2, and the enhancement of those is 23% and 28%, respectively. The improvement of device performance can be attributed to the extraction of waveguide light by the internal wrinkle pattern used as a diffraction grating. Moreover, simulation also shows that wrinkle pattern is an attractive option to improve the performances of blue QLEDs. [ABSTRACT FROM AUTHOR]

A facile and reproducible method for scalable synthesis of high‐quality core/shell quantum dots (QDs) is a prerequisite to facilitate their versatile applications. Herein, a seed‐mediated heat‐up approach is developed for the preparation of high‐quality core/shell QDs with variable shell composition and continuously tunable shell thickness by selection of conventional salts as the precursors. The method is very simple and highly reproducible and, therefore, can be easily scaled up to get gram‐level product. The as‐obtained CdSe/CdS and CdSe/ZnCdS core/shell QDs exhibit intriguing optical properties, that is a narrow photoluminescence (PL) emission peak and near‐unity PL quantum yield. Importantly, the CdSe/ZnCdS core/shell QDs with a size of 11.4 nm exhibit obviously suppressed blinking behavior, and the fraction of nonblinking QDs (defined by an on‐time fraction ≥ 0.95) can reach as high as 96.0% on the measurement of more than 200 QDs. Moreover, quantum‐dot light‐emitting diodes (QLEDs) based on CdSe/ZnCdS core/shell QDs show a peak external quantum efficiency of 14.8% and low efficiency roll‐off at luminance ranging from 1000 to 25 000 cd·m−2. It is anticipated that the presented work will pave a novel way for the large‐scale production of high‐quality QDs and further boost their applications in light‐emitting diodes, lasing, and biological imaging. [ABSTRACT FROM AUTHOR]

Blue ZnTeSe-based quantum dot light-emitting diodes (QLEDs) often suffer from poor hole injection, which significantly limits their performance. Herein, we introduced dual dipole layers consisting of (2, 3, 6, 7, 10, 11 hexaazatriphenyl hexacarbonitrile) (HAT-CN) between the hole injection layer of poly (3,4-ethylenedioxythiophene): poly (styrene sulfonate) (PEDOT: PSS) and hole transport layer of (polyvinylcarbazole) (PVK) to enhance the performance of blue ZnTeSe-based QLEDs. The introduction of the HAT-CN layer created dual dipole layers, which reduce the hole injection barrier between PEDOT: PSS and PVK, decrease the hole defect density, increase the hole current, and improve the effective radiation recombination of charge carriers. The QLEDs with the HAT-CN layer exhibited higher external quantum efficiency compared to those without the HAT-CN layer, increasing from 4.2% to 10.1%. Moreover, the T50 lifetime almost doubled at a high luminance of 2000 cd m−2. This work shows that introducing the HAT-CN layer to create dual dipole layers using the full solution method is an effective strategy for preparing high-performance ZnTeSe-based blue QLEDs. [ABSTRACT FROM AUTHOR]

The aerobic and thermal stability of quantum-dot light-emitting diodes (QLEDs) is an important factor for the practical applications of these devices under harsh environmental conditions. We demonstrate all-solution-processed amber QLEDs with an external quantum efficiency (EQE) of > 14% with almost negligible efficiency roll-off (droop) and a peak brightness of > 600,000 cd/m2, unprecedented for QLEDs fabricated under ambient air conditions. We investigate the device efficiency and brightness level at a temperature range between − 10 and 85 °C in a 5-step cooling/heating cycle. We conducted the experiments at brightness levels higher than 10,000 cd/m2, required for outdoor lighting applications. Our device performance proves thermal stability, with minimal standard deviation in the performance parameters. Interestingly, the device efficiency parameters recover to the initial values upon returning to room temperature. The variations in the performance are correlated with the modification of charge transport characteristics and induced radiative/non-radiative exciton relaxation dynamics at different temperatures. Being complementary to previous studies on the subject, the present work is expected to shed light on the potential feasibility of realizing aerobic-stable ultrabright droop-free QLEDs and encourage further research for solid-state lighting applications. [ABSTRACT FROM AUTHOR]

Top‐emitting (TE) quantum‐dot light‐emitting diodes (QLEDs) can exhibit higher light outcoupling efficiency (OCE) compared to bottom‐emitting (BE) QLEDs due to the eliminated substrate mode and enhanced microcavity effect. In this study, TE QLEDs with an OCE of over 45% are realized by simultaneously optimizing the thicknesses of both indium‐zinc‐oxide (IZO) phase tuning layers and IZO top transparent electrodes. To reduce the resistance, the IZO top electrodes are equipped with an auxiliary metal electrode. Consequently, the red QLEDs demonstrate a high external quantum efficiency (EQE) of 38.2%. Furthermore, by applying a scattering layer on the IZO top electrode, the red QLEDs demonstrate record‐breaking efficiencies of EQE 44.5%, power efficiency 92.2 lm W−1, and current efficiency 93.7 cd A−1. The proposed device architecture and optimization strategy contribute to a new design scheme for the preparation of highly efficient QLEDs for displays and lighting applications. [ABSTRACT FROM AUTHOR]

Solution‐processed quantum‐dot light‐emitting diodes (QLEDs) have achieved huge successes in terms of both efficiency and stability. However, the polymeric hole transport materials (HTMs) utilized in QLEDs, to some degree, cause severe damages to performance consistency due to their intrinsic batch‐to‐batch problems. Thus, adopting small‐molecule HTMs with definitive chemical structures and molecular weight is a plausible way to solve this issue. In this work, a new solution‐processable small‐molecule (SM)‐HTM (FLCZ) is designed and synthesized, through elaborately modifying the widely used 4,4′‐bis(carbazole‐9‐yl)‐biphenyl via manipulating dipole moments, for solution‐processed QLEDs to replace polymeric HTMs. The FLCZ‐based QLED has achieved an external quantum efficiency (EQE) of 14.63% (18.74 lm W−1, 20.01 cd A−1), approaching that of polymer HTMs‐based QLEDs. In addition, the large surface energy of 45.29 mN m−1 is also observed on the film of FLCZ, which is highly desirable for inkjet‐printed (IJP) QLED devices, results in the IJP fabricated QLED with an EQE of 10.69%. To the best of knowledge, the results of this work represent the highest device performance of conventional solution‐processed QLED based on a single SM‐HTM. [ABSTRACT FROM AUTHOR]

We consider how the device structure and the emitter properties determine the performance of near-infrared quantum dot based light-emitting diodes. The challenges and future prospects for such bright, stable and efficient devices are discussed. [Display omitted] Near-infrared (NIR) emitters are indispensable for telecommunication and medical applications. Colloidal semiconductor quantum dots offer plenty of advantages for NIR light-emitting diodes (LEDs) thanks to their size-dependent emission, high exciton binding energy, and low-cost solution processing. Here, we summarize the recent progress in the development of NIR quantum dot LEDs, focusing on how their device structure and emitter properties facilitate improvement of device performance. The challenges and opportunities associated with NIR quantum dot LEDs such as achieving the proper balance between the charge transport and exciton formation, enhancement of device stability, and improvement of device outcoupling efficiency are discussed. [ABSTRACT FROM AUTHOR]

A clear understanding on the fundamental working mechanisms of quantum‐dot light emitting diodes (QLEDs), especially the blue devices, is always sought after. Here the electroluminescence (EL) turn‐on mechanism of blue QLEDs is unraveled by structure engineering of the hole‐transport layers (HTLs). It is demonstrated that the EL turn‐on in blue QLEDs is highly dependent on the charge‐transport polarity of the HTLs. Energy transfer between HTLs and the blue quantum dots (QDs) occurs for the QLEDs based on bipolar HTLs, and, in contrast, charge injection is responsible for EL turn‐on of the blue devices consisting of unipolar HTLs. In addition, large hole‐injection barrier results in serious accumulation of holes at the interface of HTLs/QDs, then inducing serious electrons leakage into the HTLs, thereby leading to poor device efficiency under low driving current. It is suggested here that confining the carriers to the quantum dots and reducing the hole‐injection barrier remain two critical aspects to optimize the performance of blue QLEDs. [ABSTRACT FROM AUTHOR]

Quantum dot light-emitting diodes (QLEDs) have been identified as a next-generation display technology owing to their low-cost manufacturing, wide color gamut, and electrically driven self-emission properties. However, the efficiency and stability of blue QLEDs still pose a significant challenge, limiting their production and potential application. This review aims to analyse the factors leading to the failure of blue QLEDs and presents a roadmap to accelerate their development based on the progress made in the synthesis of II-VI (CdSe, ZnSe) quantum dots (QDs), III-V (InP) QDs, carbon dots, and perovskite QDs. The proposed analysis will include discussions on material synthesis, core-shell structures, ligand interactions, and device fabrication, providing a comprehensive overview of these materials and their development. [ABSTRACT FROM AUTHOR]

Novel lead-free non-perovskite blue-emitting cesium bromine (CsBr) QDs have been prepared using a ligand-assisted re-precipitation method. A high photoluminescence quantum yield of over 92.0% makes the CsBr QDs an efficient color-conversion candidate for fabricating white-light-emitting diodes. [ABSTRACT FROM AUTHOR]

Quantum dot light emitting diodes (QLEDs) emitting at 410 nm were studied by time-resolved electroluminescence measurements. A transient overshoot after voltage turn-off was seen, which is attributed to the accumulation and storage of charge carriers at the ligand-quantum dot interface. Shorter ligands showed a faster rise time and prevented the formation of an overshoot, whereas longer ligands caused the storage of charges, responded slower, and showed an overshoot. When the external voltage was switched off, the electric field between the injected and stored electrons and holes led to the occurrence of the overshoot. Applying a dual voltage pulse avoided this overshoot and instead a delayed luminescence was observed. As the accumulated charges were immobile and trapped in shallow states, a reverse pulse was applied to fully deplete the emissive layer. Because the transient overshoot disappeared after the device had been turned on, this can be used as a measure of the degradation of QLEDs. The ligands constitute a major obstacle for an efficient and long lasting blue/purple quantum dot emitter. [ABSTRACT FROM AUTHOR]

Unlike red and green quantum dot light-emitting diodes (QLEDs), it is not clear whether a blue QLED is an electron-dominated device. In this work, we identify that electron is over-injected in blue QLEDs by impedance spectroscopy. By analyzing the capacitance–voltage characteristics of the single-carrier devices, we find that the built-in voltage of the electron-only device is smaller than that of the hole-only device. Therefore, electron injection is more efficient than hole injection in blue QLEDs. To support our arguments, we employ a red QD as a fluorescent sensor to spatially investigate the exciton recombination zone of a blue QLED. Consequently, we observe that the exciton recombination zone of the blue QLED is close to the hole transport layer, and it shifts toward an electron transport layer with the increase in the applied bias. Our work provides a practical method for identifying the excess carrier in blue QLEDs, and it could be applied to other types of QLEDs. [ABSTRACT FROM AUTHOR]

Low-temperature processing is important for improving the stability and performance of flexible quantum dot light-emitting diodes (QLEDs). In this study, QLEDs were fabricated using poly[bis(4-phenyl) (2,4,6-trimethylphenyl)amine] (PTAA) as a suitable hole transport layer (HTL) material owing to its low-temperature processability and vanadium oxide as the low-temperature solution-processable hole injection layer material. The maximum luminance and highest current efficiency of the QLEDs on a glass substrate with an optimal PTAA HTL was 8.9 × 104 Cd/m2 and 15.9 Cd/A, respectively, which was comparable to that of conventional devices. The QLEDs on a flexible substrate showed a maximum luminance of 5.4 × 104 Cd/m2 and highest current efficiency of 5.1 Cd/A. X-ray and ultraviolet photoelectron spectroscopies were used to investigate the chemical state and interfacial electronic structure according to the materials and the state changes of the HTL, respectively. The interfacial electronic structure showed that PTAA exhibited a better hole transport ability owing to its low hole injection barrier ( Φ h ). Moreover, QLEDs with a PTAA HTL could operate as photosensors under reverse bias conditions. These results indicate that the low-temperature-processed PTAA HTL is suitable for improving the performance of flexible QLEDs. [ABSTRACT FROM AUTHOR]

Quantum dot light‐emitting diodes (QLEDs), regarded as promising candidates in the next‐generation display, have attracted much attention recently. In spite of the outstanding performance of cadmium‐based (Cd‐based) QLEDs, the toxicity of Cd hinders their wide application. Indium phosphide quantum dots (InP QDs) with heavy‐metal‐free feature and competitive performance are considered to be able to replace Cd‐based QDs as emitting layer in the QLEDs. Much progress is obtained in the red‐emitting and green‐emitting InP‐based QLEDs. However, the blue‐emitting ones are faced with great challenges and are demanded on full‐color display urgently, which is limited by the inferior performance of blue‐emitting InP QDs and lack of investigations about their QLED devices. In this review, the encountered challenges for high‐quality blue‐emitting InP QDs are presented. Common strategies for blue‐emitting InP QDs, including size engineering, composition engineering, and surface engineering are presented and analyzed. The progress of blue‐emitting InP‐based QLEDs, which strongly relies on the advances of materials, is also summarized. Finally, some perspectives from device physics are provided and discussed to inspire more efficient strategies toward blue‐emitting InP‐based QLEDs. [ABSTRACT FROM AUTHOR]

See‐through double‐side‐emitting electroluminescent quantum‐dot light‐emitting‐diodes (QLEDs) with highly transparent tri‐layer MoO3/Ag:Cu/MoO3 electrode is demonstrated in this study. The tri‐layer MoO3/Ag: Cu/MoO3 electrode is prepared by a thermal co‐evaporation process, in which MoO3 is utilized as both a seed layer and a capping layer. This tri‐layer structure improves the transmittance as high as ≈88% and ≈86% for pure Ag and Ag:Cu at 550 nm, respectively. It is also found that minor Cu doping significantly improves the thermal stability and sheet resistance of Ag film. With the see‐through tri‐layer film as a device cathode, transparent double‐side‐emitting green QLED exhibits remarkable high brightness of 225, 500 cd m−2, the current efficiency of 58.68 cd A−1, the external quantum yield of 16.70%, and transmittance of 77% at 550 nm without any additional anti‐reflection coating. [ABSTRACT FROM AUTHOR]

Quantum dot light‐emitting diodes (QLEDs), based on the solution‐processable colloidal quantum dots (QDs), are the high potential candidate for next generation display and lighting due to their high color purity, wide color gamut, low power consumption, and wide angle of view. Efforts have been made to improve the performance of the devices in order to achieve the goals of practical applications. This review focuses on the research progress in the materials and device physics of QLEDs, with the aims to accelerate the process of overcoming the obstacles to commercialization. Herein, the unique optical properties of QDs and the evolution of device structures are first reviewed. Then carrier dynamics, which has a decisive impact on device performance, is discussed in detail. In addition, the main obstacle to commercialization is emphasized as device stability, including operational stability, shelf stability, and efficiency roll‐off. Finally, unresolved issues in device physics are discussed, along with suggestions for future research directions. This review is expected to encourage further research in device physics and promote the development of QLEDs in the field of display and solid‐state lighting. [ABSTRACT FROM AUTHOR]

Highlights: Quantum dots light emitting devices (QLEDs) with extremely long half-lifetimes at 100 cd m−2, 2,370,000 h were successfully fabricated using CF4 plasma-treated ZnO nanoparticle electron transport layers. A new experimental approach that probes changes in exciton lifetime under current flow was used to investigate the changes in carrier concentration in QLEDs. Evidence of the dependence of QLED stability on electron and hole concentrations at the QD/HTL interface was revealed. ZnO nanoparticles are widely used for the electron transport layers (ETLs) of quantum dots light emitting devices (QLEDs). In this work we show that incorporating fluorine (F) into the ZnO ETL results in significant enhancement in device electroluminescence stability, leading to LT50 at 100 cd m−2 of 2,370,000 h in red QLED, 47X longer than the control devices. X-ray photo-electron spectroscopy, time-of-flight secondary ion mass spectroscopy, photoluminescence and electrical measurements show that the F passivates oxygen vacancies and reduces electron traps in ZnO. Transient photoluminescence versus bias measurements and capacitance–voltage-luminance measurements reveal that the CF4 plasma-treated ETLs lead to increased electron concentration in the QD and the QD/hole transport layer interface, subsequently decreasing hole accumulation, and hence the higher stability. The findings provide new insights into the critical roles that optimizing charge distribution across the layers play in influencing stability and present a novel and simple approach for extending QLED lifetimes. [ABSTRACT FROM AUTHOR]

Impedance spectroscopy is a powerful and nondestructive tool for studying charge carrier dynamics in quantum dot light-emitting diodes (QLEDs). We report here that QLEDs exhibit unique capacitance behavior that strongly depends on the ligand chemistry of the quantum dots (QDs). At low frequencies and under bipolar injection, the capacitance of the QLEDs becomes negative before it returns to positive values at even lower frequencies. This behavior is fundamentally different from that observed in organic light-emitting diodes and is attributed to the accumulation of charge carriers within the ligand shells during operation. The capacitive response depends on both the conductivity and the length of the QD ligands and can be used as a diagnostic tool for understanding the luminescent recombination efficiency of a QLED. We find that short and conductive ligands result in positive device capacitances only and this correlates with enhanced device efficiency. [ABSTRACT FROM AUTHOR]

The quantum dot (QD) light emitting diode has emerged as one of the candidates for the next generation display technology with advantages such as tunable wavelength of emitted light and narrow bandwidth. For QD pixel patterning, inkjet-printing is superior to other methods in terms of material loss and process time. However, inkjet-printing has difficulty in controlling the uniformity of the QD layer. This is a serious issue considering that proper thickness and uniformity of the QD layer are important factors for high efficiency in displays. The main reason behind this problem is known to be the coffee ring effect (CRE), in which differential evaporation across a sessile droplet leads to an edge-ward flow of the fluid inside and causes suspending QDs to be concentrated at the perimeter of the droplet. Here, the possibility of improvement in layer uniformity by the reduction of the CRE is demonstrated. Mathematical simulation of the evaporation process of the QD colloidal solution droplet is conducted by solving partial differential equations (PDEs) numerically. The Navier-Stokes equation, continuity condition, and mathematical expressions of physical parameters including the evaporative flux are used for setting up the PDEs, which are then solved with the finite difference method. A filter is included in the process to suppress unwanted instability. Using this simulation, the whole evaporation process is analyzed by observing time evolution of parameters. As a result, various conditions for reducing the CRE are found: sufficient initial concentration, proper solvent type, small contact angle, and fast evaporation rate. The outcome appears to agree with experimental data. [ABSTRACT FROM AUTHOR]

Herein, the outstanding efficiency of solution‐processed quantum‐dot (QD) light‐emitting diodes (QLEDs) is demonstrated, which is achieved by adjusting the thickness of their Zn0.9Mg0.1O nanoparticle (NP) electron transport layer (ETL).The NPs are prepared by the sol‐gel method. As the thickness increases, the current density of the QLEDs decreases because of the increased resistance of the Zn0.9Mg0.1O NP ETL. As the thickness increases from 10 to 35 nm, the luminance, luminous efficiency, and external quantum efficiency (EQE) also increase because of the improved charge balance between electrons and holes in the QD emissive layer (EML). In contrast, as the thickness increases beyond 35–120 nm, these three variables decrease because of the worsening charge balance, which is attributing to deficient electron injection from the cathode into the QD EML compared with hole injection from the anode into the EML. The QLED with a 35 nm thick Zn0.9Mg0.1O NP ETL exhibits the highest luminance, luminous efficiency, and EQE, with values of 128 084 cd m−2, 88.8 cd A−1, and 21.3%, respectively. The superior device performance and good charge balance to the appropriate ETL thickness are attributed. [ABSTRACT FROM AUTHOR]

Cadmium‐free quantum dot light‐emitting diodes (QLEDs) have held the potential to revolutionize the next‐generation displays with their advantages in color gamut, luminance intensity, and solution processibility. As a promising way of realizing large‐area QLED display production, inkjet printing has been intensively studied on Cd‐based QLEDs but lacks exploration in fabricating Cd‐free devices. Here, we developed Cd‐free RGB inkjet‐printed QLEDs with tailored hole transport layers (t‐HTLs) using Cd‐free QDs including InP/ZnSeS red and green QDs and ZnTeSe/ZnSe/ZnS blue QDs. With the t‐HTLs, QD ink erosion on the bottom charge transport layer was remarkably suppressed, while the efficient hole transport was maintained, which kept high device performance, especially in the QLED lifetime. With bank structures, Cd‐free QLED pixels were well defined within the size of 60 μm × 160 μm. Based on the t‐HTL structure and the bank structures, inkjet‐printed Cd‐free RGB QLED pixel arrays were demonstrated. This study bridges the gap between existing Cd‐free QLED technologies and the future commercialization of Cd‐free self‐emissive QD displays. [ABSTRACT FROM AUTHOR]

To understand the exciton dynamics due to the electron delocalization in InP‐based quantum dot light‐emitting diodes (QLEDs), the exciton dynamics are systematically controlled in InP‐based QLEDs through varying the shell thicknesses of InP/ZnSe quantum dots (QDs) and the effective electrical field (E‐field) across the QDs. It is found that the field‐independent energy transfer is effectively suppressed as the shell thickness increases. However, InP/ZnSe QDs with thicker shells only have limited benefit for suppressing the exciton transfer due to field‐enhanced electron delocalization in films on electron transport layers or working devices. The field‐assisted exciton transfer is mainly driven by the large E‐field and field‐enhanced electron delocalization in InP/ZnSe QDs. External quantum efficiency of 22.56% is achieved in InP‐based QLEDs by reducing the effective E‐field (at 2 V bias). The breakthrough luminance of 136 090 cd/m−2 is achieved at a large bias of 7.2 V, due to the suppression of field‐enhanced electron delocalization by the ultra‐thick shell. [ABSTRACT FROM AUTHOR]

The inadequate hole injection limits the efficiency and lifetime of the blue quantum dot light‐emitting diodes (QLEDs), which severely hampers their commercial applications. Here a new discotic molecule of 3,6,10,11‐tetrakis(pentyloxy)triphenylene‐2,7‐diyl bis(2,2‐dimethylpropanoate) (T5DP‐2,7) is introduced, in which the hole transport channels with superior hole mobility (2.6 × 10–2 cm2 V–1 s–1) is formed by stacking. The composite hole transport material (HTM) is prepared by blending T5DP‐2,7 with the cross‐linked 4,4′‐ bis(3‐vinyl‐9H‐carbazol‐9‐yl)‐1,1′biphenyl (CBP‐V) which shows the deep highest occupied molecular orbital energy level. The increased hole mobility of the target composite HTM from 10–4 to 10–3 cm2 V–1 s–1 as well as the stepwise energy levels facilitates the hole transport, which would be beneficial for more balanced carrier injection. This composite hole transport layer (HTL) has improved the deep‐blue‐emission performances of Commission International de I'Eclairage of (0.14, 0.04), luminance of 44080 cd m−2, and external quantum efficiency of 18.59%. Furthermore, when L0 is 100 cd m−2, the device lifetime T50 is extended from 139 to 502 h. The state‐of‐the‐art performance shows the successful promotion of the high‐efficiency for deep blue QLEDs, and indicates that the optimizing HTL by discotic molecule stacking can serve as an excellent alternative for the development of HTL in the future. [ABSTRACT FROM AUTHOR]

Colloidal quantum dot light‐emitting diodes (QLEDs) simultaneously exhibiting high external quantum efficiency (EQE) and operation stability are achieved via a simple solution processing. A silver bis(trifluoromethane‐sulfonyl)imide treatment that is used to chemically dope the poly(3,4‐ethylenedioxythiophene):poly(4‐styrenesulfonate) (PEDOT:PSS) hole injection layer (HIL) is proposed. The ionic liquid salt acts as an effective p‐dopant for high charge concentrations; and it raises the work functions and surface potentials of the PEDOT:PSS HIL for an interface energy band alignment. Benefiting from a raised hole mobility and a better charge mobility balance, the processing‐simple colloidal red QLEDs yielded the highest EQE of up to 17.4%. In particular, a very broad plateau of EQE values over 16.5% in the brightness of 400–10 000 cd m−2 is obtained. Moreover, the packaged QLEDs exhibit an excellent operation stability in ambient air. The T95 (time for the device brightness to decrease to 95% of its initial brightness) at an initial brightness of 1000 cd m−2 is 4160 h. The work highlights a promising ionic liquid strategy to guide the development of high‐performance and cost‐effective QLEDs. [ABSTRACT FROM AUTHOR]

Effective p‐type doping is essential to enhance hole transport and balance electron–hole injection in quantum dot light‐emitting diodes (QLEDs). Here, an oligothiophene material is adopted as a p‐type dopant in the hole‐transport layer, considering its cruciform cross‐center structure, precise molecular weight, and high purity. Compared with the dopant‐free counterpart, hole transport capability at the optimal doping level exhibits a significant improvement, producing a boosted external quantum efficiency (EQE) and luminance up to 20.8%, 213 439 cd m–2, respectively, among the highest reported on the red‐light emission. The work indicates the potential applications of oligothiophene material in red light‐emitting devices. [ABSTRACT FROM AUTHOR]

[Display omitted] • A NH 4 F-assisted synthesis strategy is proposed, for the first time, achieving near-unity photoluminescence quantum yield in pure blue ZnSeTe QDs. • The mechanism of the NH 4 F treatment on the photoluminescence properties of ZnSeTe QDs is systematically investigated and understood. • By using these ZnSeTe QDs as the emitting layer, an external quantum efficiency of 16.3% for an inverted structure QLED and 17.2% for a standard structure QLED was achieved. ZnSeTe quantum dots (QDs) show promise in advancing high-performance pure blue quantum dot light-emitting diodes (QLEDs) for high-definition displays, owing to their exceptional luminescent properties and environmental characteristics. However, the current most efficient synthesis method involves a challenging and hazardous step: injecting water-based hydrofluoric acid treatment under high-temperature conditions. Herein, a novel approach utilizing inorganic fluoride NH 4 F as a molecular additive is introduced to simplify the synthesis of highly efficient ZnSeTe/ZnSe/ZnS blue QDs. The resulting QDs exhibit tunable photoluminescence (PL) wavelengths in the pure blue region with near-unit PL quantum yield (QY). Notably, the use of NH 4 F passivates the ZnSeTe cores, enhancing stability and facilitating high-quality coating of the subsequent shell layer, ultimately reducing nonradiative recombination rates and improving PL QY. To evaluate the practical application of these blue ZnSeTe/ZnSe/ZnS QDs, we utilized them as an emitting layer to fabricate QLEDs with two typical structures. The results demonstrated that the external quantum efficiency of the standard QLED and inverted QLED can reach 17.2% and 16.3%, respectively, showing comparable performance to QLEDs with QDs prepared through classical HF addition synthesis steps. This environmentally friendly synthesis strategy for pure blue ZnSeTe QDs with high PL QY through NH 4 F assistance is expected to offer insights for synthesizing other environmentally friendly QDs, thus facilitating the development of eco-friendly QLEDs. [ABSTRACT FROM AUTHOR]

In this work, we designed and synthesized two new hole-transporting materials with a nonplanar three-dimensional (3D) conformation. They were achieved by incorporating spiro[fluorene-9,9′-xanthene] as a cross-shaped configuration scaffold and adding either mono- (H1) or bis- benzodioxino[2,3-b]pyrazine (H2) pyrazine as pendant groups. Both compounds exhibit remarkable thermal stability, with thermal decomposition temperature (T d) of 462 (H1) and 504 °C (H2), respectively. Moreover, the structural substitution with benzodioxino[2,3-b]pyrazine units successfully aligned the energy levels of both materials with the perovskite quantum dot luminescence layer. Hereby, the fabricated perovskite QLEDs using H1 as hole-transporting materials (HTMs) featured an excellent average external quantum efficiency (EQE) of up to 9.5% with a maximum luminance of 22368 cd m−2, which is much higher than that of the H2 -based devices with an EQE of 6.6% under the same conditions. The excellent device performance from H1 can be attributed to its asymmetric structure by the introduction of monosubstituted benzodioxino[2,3-b]pyrazine groups, as evidenced by its high hole mobility of 1.90 × 10−4 cm2 V−1 s−1 and improved interface interaction with adjunct layers. Thus, this design approach may bring a fresh perspective to the utilization of solution-processable small-molecule HTMs in high-performance Pe-QLEDs and other optoelectronics in the future. [Display omitted] • Two spirofluorene-based hole transport materials with pyrazine were developed. • Both materials reveal excellent thermal stability, featuring high T g and T d. • They exhibit good hole transport capability and suitable energy level alignment. • Perovskite green QLEDs using single-pyrazine H1 achieved nearly 9.5% EQE avg. [ABSTRACT FROM AUTHOR]