Air-Processed Perovskites Enabled by an Interface-Reconstruction Strategy for High-Performance Light-Emitting Diodes.

Improvement of color-rendering characteristics of white light emitting diodes by using red quantum dot films

Light-emitting diodes (LEDs) based on perovskite quantum dots (QDs) have achieved external quantum efficiencies (EQEs) exceeding 20% at a practical luminance (>1000 cd m-2) for real-world applications in the green and red regions. However, the pure-blue perovskite QD LEDs still suffer from low efficiency at high luminance: the EQE of the reported best device at 600 cd m-2 is below 7.0%. One of the limiting factors is weak ligand-surface binding because of the dynamic ligand-binding nature. In this work, we employ first-principles calculations to evaluate the hard-soft-acid-base interaction strength and search for the appropriate alkali metal ions to resolve this limiting factor. We found that rubidium ions have the most compatible softness with bromine dangling bonds in the strongly confined QDs, leading to stronger bonding. This strategy enabled the photoluminescence quantum yield of the QD film to be 81%. The low-defect QD films ensured efficient carrier recombination, enabling pure-blue perovskite QD LEDs to generate an EQE peak of 15.7% with a luminance of 3916 cd m-2, and the EQE remains at 14.9% under a higher luminance of 5371 cd m-2. This represents an achieved record EQE × luminance: a 35-fold improvement compared to the best previous pure-blue perovskite LED.

A remote-type white light-emitting diode (LED) consisting of a red quantum-dot (QD) film and a yellow phosphor plate was studied by both experiment and optical simulation. The sequence of the two color-conversion films had a substantial effect on the color-rendering properties of the vertically-stacked white LED, and the optimized configuration exhibited a high color rendering index of more than 90 thanks to the enhanced red component via the QD film. For the design of high-power white LED devices of a remote type, it was necessary to locate the color-conversion films below the diffuser plate to remove the substantial color dispersion depending on the viewing angle. The present study shows that high power and high color-rendering white LED devices can be realized in terms of two vertically-stacked color-conversion materials, which would provide long-term stability due to the remote design.

Eliminating lattice disorder in quantum dots (QDs) is critical for achieving high‐performance quantum dot light‐emitting diodes (QLEDs), as such disorder directly disrupts the uniformity of elemental distribution and degrades their optical properties. Here, a tertiary amine‐mediated synthesis strategy is reported that utilizes nucleophilic reagents to regulate the coordination kinetics of cationic precursors during the growth of ZnCdSeS/ZnS QDs. This strategy leverages nucleophilic reagents bearing uncoordinated lone‐pair electrons to stabilize the cationic precursors and modulate the QDs surface energy of highly reactive crystal planes, thereby promoting atomic‐scale uniform growth of the QDs, minimizing lattice mismatch, preventing stacking faults, and thus enabling the synthesis of strain‐graded QDs ( sg ‐QDs). Consequently, by achieving precise control over both elemental distribution and lattice ordering in multicomponent alloy QDs, sg ‐QDs are obtained that exhibit a photoluminescence quantum yield of 98% in solution and 95% in the solid film. The sg ‐QD films further demonstrate monoexponential decay kinetics and reduced defect density, confirming effective trap‐state suppression. The resultant green QLEDs achieve a record external quantum efficiency (EQE) of 25.2%, an operational lifetime of 1 925 900 h, and sustained EQE over 20% across a luminance range of 10 2 –10 5 cd m −2 . This nucleophile‐coordination paradigm redefines the synthesis of alloy nanocrystals, providing a dual‐advantage platform for ultrastable optoelectronics and scalable QLEDs manufacturing.

The enhancement of optical properties via thermal annealing on InP/ZnS core/shell quantum dot (QD) film was investigated in this work. The increase of emission intensities of the QD films was observed after thermal annealing at 180 °C for 5 min. Through temperature dependence photoluminescence (TDPL) and power dependence photoluminescence (PL) measurement, the peak located at the low-energy shoulder was confirmed to be localized state emission and the high energy one comes from free-carrier emission. Moreover, from the TDPL spectra of the sample annealed at 180 °C for 5 min, the full width at half maximum (FWHM) of localization state emission was nearly the same before which is 250 K and then decreased with increasing temperature. However, the FWHM was decreased significantly when temperature increased in the untreated sample. We conclude that the escape of localization states with increasing temperature contributes to this anomaly phenomenon. Our studies have significance on the application of QDs in electroluminescence devices and down-conversion light-emitting devices.

This Letter proposes a dual-wavelength, low-coherence digital holography system with a single light source, which utilizes a quantum dot (QD) film as a wavelength converter. By changing the size of the QDs, the proposed method easily yields higher and more uniform illumination of any target wavelength, compared with bandpass-filtered light-emitting diodes. Fabrication parameters of the QD film for better conversion efficiency are discussed. Using this light source with the dual-wavelength reconstruction method extends the efficiency and range of nanoscale three-dimensional height measurements.

This work reports the design of a 60-segment photoluminescence quantum dot light emitting device (QD-LED) for automotive lighting systems. The QD-LED device was fabricated using a quantum dot film (QDF), incorporating two kinds of quantum dots (QDs) synthesized to emit at 531 nm (green) and 624 nm (red). When the QDF is excited with blue wavelength at 465 nm, a white color output is obtained. Likewise, by using different color filters, all the automotive lighting functions (interior and exterior) can be achieved. In addition, an electronic control module, based on the state-of-the-art multichannel automotive lighting emitting diode (LED) drivers, was specifically designed to control each segment individually to enable the possibility of external digital communication with the vehicle surroundings. That is key to develop the autonomous vehicle by incorporating what is known as car-to-X communication, used to transmit information to other vehicles and road users through light. Furthermore, this work is remarkable due to the low power consumption of the QD-LED device designed, which implies a high electrical efficiency, something critical for the electrical vehicle development. Besides, figures of merit and performance indicators are measured, offering promising values to use this nanotechnology in the next future of the vehicle transportation lighting systems.

Poly[(9,9-dioctylfluorenyl-2,7-diyl)-alt(4,4′-(N-(4-butylphenyl))] (TFB), one of the most popular and widely used hole-transport layer (HTL) materials, has been successfully applied in high performance spin-coated quantum dots-based light-emitting diodes (QLEDs) due to its suitable energy level and high mobility. However, there are still many challenging issues in inkjet-printed QLED devices when using TFB as HTL. TFB normally suffers from the interlayer mixing and erosion, and low surface energy against the good film formation. Here, a novel environment-friendly binary solvent system was established for formulating quantum dot (QD) inks, which is based on mixing halogen-free alkane solvents of decalin and n-tridecane. The optimum volume ratio for the mixture of decalin and n-tridecane was found to be 7:3, at which a stable ink jetting flow and coffee-ring free QD films could be formed. To research the influence of substrate surface on the formation of inkjet-printed QD films, TFB was annealed at different temperatures, and the optimum annealing temperature was found to enable high quality inkjet-printed QD film. Inkjet-printed red QLED was ultimately manufactured. A maximum 18.3% of external quantum efficiency (EQE) was achieved, reaching 93% of the spin-coated QLED, which is the best reported high efficiency inkjet-printed red QLEDs to date. In addition, the inkjet-printed QLED achieved similar T75 operational lifetime (27 h) as compared to the spin-coated reference QLED (28 h) at 2,000 cd·m−2. This work demonstrated that the novel orthogonal halogen-free alkane co-solvents can improve the interfacial contact and facilitate high-performance inkjet printing QLEDs with high EQE and stability.

Quantum dots (QDs) are investigated for photovoltaic (PV) device applications; due to safety concerns regarding the use of Cd, Pb-based materials, less-toxic copper indium sulfide (CIS) and zinc copper indium sulfide (ZCIS) QDs have gained prominence. In advanced PV structures, the formation and morphology of QD films is significant; the construction of uniform, defect-free QD films are desirable. Several strategies are employed in QD film formation, most notably spin-casting, drop-casting, and dip-coating. We studied the film deposition and self-assembly QDs in formation of device-quality films. Using dip-coating, we developed a method to deposit uniform, ordered less-toxic CIS and ZCIS QD films for large-area, scaled-up PV applications.

Photovoltaic effects in CdSe quantum dot (QD) films have been studied using surface photovoltage spectroscopy and complementary methods. The results show that, contrary to previous studies, nonnegligible electric fields can exist in QD films. As a result, driftlike currents must be considered, in addition to the well‐known diffusionlike currents. However, it is found that the specific case of photovoltage sign reversal, observed after etching highly quantized CdSe QD films, is governed by diffusionlike transport. The latter is highly influenced by preferential trapping of one type of charge carrier. The preferential trapping is shown to be surface localized and is strongly ambient dependent. It is shown that the photovoltaic properties of these CdSe QD films are dominated by their surface state distribution.

Quantum dots (QDs) have extraordinary strong light absorption and size tunable bandgap. However, QD films are typically limited to ~200-300 nm due to their poor charge mobility. This severely limits the quantum efficiency of QD devices for λ <750 nm (infrared). Herein, we report a record 1 μm thick QD film using intercalated graphene layers as transparent current extractors. This overcomes QD poor mobility, ensuring both effective light absorption and charge extraction towards the near-infrared reaching quantum efficiency (EQE) of 90%. The short diffusion length (LD<200 nm) of QDs limits their useful thickness to ~200-300 nm1–4 , resulting in poor infrared light absorption. To overcome this limitation, we have built a 1 µm thick QD film with intercalated transparent graphene electrodes that keep high charge collection efficiency. As a result, the 1 µm intercalated devices show a superior EQE reaching 90% at λ ~800 nm without the drop of quantum efficiency at λ ~700 nm observed in most QD devices. The EQE of intercalated devices improves over the entire λ~ 600-1100 nm spectrum as the thickness increases from 100 nm to 1 μm, clearly breaking the restriction that the diffusion length of QDs imposes on the film thickness. This improves absorption and charge collection in the infrared.

The surface organic ligands of the quantum dots (QDs) play important roles in the performance of QD electronic devices. Here, we fabricated low toxic AgIn5S8/ZnS QDs light-emitting diodes (QD-LEDs) and greatly enhanced the device efficiency through surface ligand exchange treatments. The oleic acid-capped QDs were replaced with a shorter ligand 1,2-ethanedithiol, which was proved by the Fourier transform infrared spectrum measurement. The treated QD films became more compact with higher film mobility and shorter film photoluminescence lifetime. The more conductive QD films fabricated LEDs showed an external quantum efficiency over 1.52%.

Near-infrared (NIR)-emitting PbS-based quantum dots (QDs) and exfoliated layered double hydroxide (LDH) nanosheets were self-assembled to form photostable composites for NIR-emitting codes. PbS QDs prepared by a pyrolysis synthetic method or PbS–CdS (core–shell) QDs prepared by a cation exchange using PbS QDs were transferred to aqueous solutions by surface ligand exchange to dihydrolipoic acid (DHLA). The DHLA-decorated QDs and exfoliated LDH nanosheets were assembled by electrostatic interactions during vortexing. The QD–LDH composite films prepared by drop-casting exhibit more than 500% higher NIR PL intensities than the counterpart QD films (without LDH matrices) under identical conditions (i.e., QD concentration). Photostability tests under continuous light irradiation reveal that the PbS–CdS QD films are more photostable than the PbS QD films. Formation of the QD–LDH composites gives rise to further enhancement in the photostability of the film. The photostable PbS–CdS QD–LDH composite films were used to create novel NIR-emitting codes. NIR fluorescence images of a pattern of two kinds of PbS–CdS QD–LDH composite films were recorded with an InGaAs CCD camera equipped with optical filters.

Quantum dots (QDs) have received considerable attention in information displays owing to their high quantum yield, high colour purity and low-cost fabrication. However, light emission for ultra-thin QD films with low mass percentage of QDs still need to be improved because the blue light can directly transmit the films, leading to insufficient energy to excite the QDs. In this study, we report QD films based on a poly(zinc methacrylate) coating with alloyed green-emitting CdZnSeS/ZnS quantum dots (QDs@PZnMA) together with high refractive-index BaTiO3 nanoparticles to enhance the scattering coefficient of the QD films. Results demonstrate a 7.5-fold increase in the absorption coefficient, 11.3-fold increase in the scattering coefficient, 8.5-fold increase in the optical density (OD) and 8.6-fold increase in the green-light emission of QD films, compared with films that have the same mass percentage of pristine QDs. This approach provides a promising strategy for developing QD optical films with high scattering and enhanced light emission for flexible displays.

In this work, trioctylphosphine oxide (TOPO) ligand is employed to improve the quality of CsPbBr1.2I1.8 quantum dots (QDs) films. Lead nitrate (Pb(NO3)2) is also used to passivate the surface of the films. The study of ligand and surface passivation on the luminous efficiency of red light-emitting diode (LED) is discussed. The CsPbBr1.2I1.8 QDs films co-doped with TOPO and Pb(NO3)2 can effectively improve the performance of the CsPbBr1.2I1.8 QDs LEDs due to reduction of non-radiation recombination of the carriers and smooth morphology in the active layer, thus improving the injection and transportation capabilities of carriers. As a result, the highest luminosity and current efficiency are 502.7 cd/m2 and 0.175 cd/A, respectively.