Ligand-Crosslinking Strategy for Efficient Quantum Dot Light-Emitting Diodes via Thiol-Ene Click Chemistry

Intrinsically-Stretchable and Patternable Quantum Dot Color Conversion Layers for Stretchable Displays in Robotic Skin and Wearable Electronics

Stretchable displays are essential components as signal outputs in next-generation stretchable electronics, particularly for robotic skin and wearable device technologies. Intrinsically-stretchable and patternable color conversion layers (CCLs) offer practical solutions for developing full-color stretchable micro-light-emitting diode (LED) displays. However, significant challenges remain in creating stretchable and patternable CCLs without backlight leakage under mechanical deformation. Here, a novel material strategy for stretchable and patternable heavy-metal-free quantum dot (QD) CCLs, potentially useful for robotic skin and wearable electronics is presented. Through a versatile crosslinking technique, uniform and high-concentration QD loading in the elastomeric polydimethylsiloxane matrix without loss of optical properties is achieved. These CCLs demonstrate excellent color conversion capabilities with minimal backlight leakage, even under 50% tensile strain. Additionally, fine-pixel patterning process with resolutions up to 300 pixels per inch is compatible with the QD CCLs, suitable for high-resolution stretchable display applications. The integration of these CCLs with micro-LED displays is also demonstrated, showcasing their use in haptic-responsive robotic skin and wearable healthcare monitoring sensors. This study offers a promising material preparation methodology for stretchable QDs/polymer composites and highlights their potential for advancing flexible and wearable light-emitting devices.

Tailoring the Interfacial Composition of Heterostructure InP Quantum Dots for Efficient Electroluminescent Devices

The formation of core-shell quantum dots (QDs) with type-I band alignment results in surface passivation, ensuring the efficient confinement of excitons for light-emitting applications. In such cases, the atomic composition at the core-shell heterojunction significantly affects the optical, and electrical properties of the QDs. However, for InP cores, shell materials are limited to compositions consisting of II-VI group elements. The restricted selection of shell materials leads to an interfacial misfit, resulting in a charge imbalance at the core-shell heterojunction. In this study, the effect of interfacial stoichiometry is investigated on the optical, and electrical properties of InP core-shell QDs. Direct Se injection strategy is employed during the synthesis of the InP core to regulate the interfacial chemical composition, resulting in the formation of an InZnSe alloy on the core surface. This InZnSe layer reduces the misfit between the InP core, and ZnSe shell, leading to a remarkable photoluminescence quantum yield of 95% with a narrow emission bandwidth of 34 nm. The InZnSe interlayer significantly influences the electroluminescence (EL) processes, increasing the charge injection efficiency, and mitigating charge imbalance. A green-emitting EL device is demonstrated with a maximum luminance of 26370 cd m-2, and a peak current efficiency of 31.5 cd A-1.

Ring-Opening Polymerization of Surface Ligands Enables Versatile Optical Patterning and Form Factor Flexibility in Quantum Dot Assemblies

The evolution of display technologies is rapidly transitioning from traditional screens to advanced augmented reality (AR)/virtual reality (VR) and wearable devices, where quantum dots (QDs) serve as crucial pure-color emitters. While solution processing efficiently forms QD solids, challenges emerge in subsequent stages, such as layer deposition, etching, and solvent immersion. These issues become especially pronounced when developing diverse form factors, necessitating innovative patterning methods that are both reversible and sustainable. Herein, a novel approach utilizing lipoic acid (LA) as a ligand is presented, featuring a carboxylic acid group for QD surface attachment and a reversible disulfide ring structure. Upon i-line UV exposure, the LA ligand initiates ring-opening polymerization (ROP), crosslinking the QDs and enhances their solvent resistance. This method enables precise full-color QD patterns with feature sizes as small as 3 µm and pixel densities exceeding 3788 ppi. Additionally, it supports the fabrication of stretchable QD composites using LA-derived monomers. The reversible ROP process allows for flexibility, self-healing, and QD recovery, promoting sustainability and expanding QD applications for ultra-fine patterning and on-silicon displays.

Patterning technologies of quantum dots for color-conversion micro-LED display applications

Quantum dot (QD) materials and their patterning technologies play a pivotal role in the full colorization of next-generation Micro-LED display technology. This article reviews the latest development in QD materials, including II-VI group, III-V group, and perovskite QDs, along with the state of the art in optimizing QD performance through techniques such as ligand engineering, surface coating, and core-shell structure construction. Additionally, it comprehensively covers the progress in QD patterning methods, such as inkjet printing, photolithography, electrophoretic deposition, transfer printing, microfluidics, and micropore filling method, and emphasizes their crucial role in achieving high precision, density, and uniformity in QD deposition. This review delineates the impact of these technologies on the luminance of QD color-conversion layers and devices, providing a detailed understanding of their application in enhancing Micro-LED display technology. Finally, it explores future research directions, offering valuable insights and references for the continued innovation of full-color Micro-LED displays, thereby providing a comprehensive overview of the potential and scope of QD materials and patterning technologies in this field.

Direct Photopatterning of Colloidal Quantum Dots with Electronically Optimized Diazirine Cross-Linkers

Colloidal quantum dots (QDs) with a wide color gamut and high luminescent efficiency are promising for next-generation electronic and photonic devices. However, precise and scalable patterning of QDs without degrading their properties and their integration into commercially relevant devices, such as digitally addressable QD light-emitting diode (QLED) displays, remain challenging. Here, we develop electronically optimized diazirine-based cross-linkers for nondestructive, direct photopatterning of QDs and, ultimately, building the active-matrix QLED displays. The key to the cross-linker design is the introduction of electron-donating substituents that permit the formation of ground-state singlet carbenes for air-stable and benign QD photopatterning. Under ambient conditions, these cross-linkers enable the patterning of heavy metal-free QDs at a resolution of over 13,000 pixels per inch using commercial i-line photolithography. The patterned QD layers fully preserved their optical and optoelectronic properties. Pixelated electroluminescent devices with patterned InP/ZnSe/ZnS QD layers show a peak external quantum efficiency of 15.3% and a maximum luminance of about 40,000 cd m-2, outperforming those made by existing QD patterning approaches. We further show the seamless integration of patterned QLEDs with thin-film transistor circuits and the fabrication of dual-color active-matrix displays. These results underscore the importance of designing photochemistry for QD patterning, and promise the implementation of direct photopatterning methods in manufacturing commercial QLED displays and other integrated QD device platforms.

Ligand-Nondestructive Direct Photolithography Assisted by Semiconductor Polymer Cross-Linking for High-Resolution Quantum Dot Light-Emitting Diodes

The photolithographic patterning of fine quantum dot (QD) films is of great significance for the construction of QD optoelectronic device arrays. However, the photolithography methods reported so far either introduce insulating photoresist or manipulate the surface ligands of QDs, each of which has negative effects on device performance. Here, we report a direct photolithography strategy without photoresist and without engineering the QD surface ligands. Through cross-linking of the surrounding semiconductor polymer, QDs are spatially confined to the network frame of the polymer to form high-quality patterns. More importantly, the wrapped polymer incidentally regulates the energy levels of the emitting layer, which is conducive to improving the hole injection capacity while weakening the electron injection level, to achieve balanced injection of carriers. The patterned QD light-emitting diodes (with a pixel size of 1.5 μm) achieve a high external quantum efficiency of 16.25% and a brightness of >1.4 × 105 cd/m2. This work paves the way for efficient high-resolution QD light-emitting devices.

Direct photocatalytic patterning of colloidal emissive nanomaterials

We present a universal direct photocatalytic patterning method that can completely preserve the optical properties of perovskite nanocrystals (PeNCs) and other emissive nanomaterials. Solubility change of PeNCs is achieved mainly by a photoinduced thiol-ene click reaction between specially tailored surface ligands and a dual-role photocatalytic reagent, pentaerythritol tetrakis(3-mercaptopropionate) (PTMP), where the thiol-ene reaction is enabled at a low light intensity dose (~ 30 millijoules per square centimeter) by the strong photocatalytic activity of PeNCs. The photochemical reaction mechanism was investigated using various analyses at each patterning step. The PTMP also acts as a defect passivation agent for the PeNCs and even enhances their photoluminescence quantum yield (by ~5%) and photostability. Multicolor patterns of cesium lead halide (CsPbX3)PeNCs were fabricated with high resolution (<1 micrometer). Our method is widely applicable to other classes of nanomaterials including colloidal cadmium selenide-based and indium phosphide-based quantum dots and light-emitting polymers; this generality provides a nondestructive and simple way to pattern various functional materials and devices.