Establishing multi-colour patterning technology for colloidal quantum dots is critical for realising high-resolution displays based on the material. Here, we report a solution-based processing method to form patterns of quantum dots using a light-driven ligand crosslinker, ethane-1,2-diyl bis(4-azido-2,3,5,6-tetrafluorobenzoate). The crosslinker with two azide end groups can interlock the ligands of neighbouring quantum dots upon exposure to UV, yielding chemically robust quantum dot films. Exploiting the light-driven crosslinking process, different colour CdSe-based core-shell quantum dots can be photo-patterned; quantum dot patterns of red, green and blue primary colours with a sub-pixel size of 4 μm × 16 μm, corresponding to a resolution of >1400 pixels per inch, are demonstrated. The process is non-destructive, such that photoluminescence and electroluminescence characteristics of quantum dot films are preserved after crosslinking. We demonstrate that red crosslinked quantum dot light-emitting diodes exhibiting an external quantum efficiency as high as 14.6% can be obtained.

A semicrystalline p-type thermoelectric conjugated polymer based on a polymer backbone of cyclopentadithiophene and benzothiadiazole, poly­[(4,4′-(bis­(hexyldecyl­sulfanyl)­methylene)­cyclopenta­[2,1-b:3,4-b′]­dithiophene)-alt-(benzo­[c]­[1,2,5]­thiadiazole)] (PCPDTSBT), is designed and synthesized by replacing normal alkyl side-chains with bis­(alkylsulfanyl)­methylene substituents. The sp2-hybridized olefinic bis­(alkylsulfanyl)­methylene side-chains and the sulfur–sulfur (S–S) chalcogen interactions extend a chain planarity with strong interchain packing, which is confirmed by density functional calculations and morphological studies, i.e., grazing incidence X-ray scattering measurement. The doping, electrical, morphological, and thermoelectric characteristics of PCPDTSBT are investigated by comparison with those of poly­[(4,4′-bis­(2-ethylhexyl)­cyclopenta­[2,1-b:3,4-b′]­dithiophene)-alt-(benzo­[c]­[1,2,5]­thiadiazole)] (PCPDTBT) with ethylhexyl side-chains. Upon doping with a Lewis acid, B­(C6F5)3, the maximum electrical conductivity (7.47 S cm–1) of PCPDTSBT is ∼1 order higher than that (0.65 S cm–1) of PCPDTBT, and the best power factor is measured to be 7.73 μW m–1 K–2 for PCPDTSBT with doping 9 mol % of B­(C6F5)3. The Seebeck coefficient–electrical conductivity relation is analyzed by using a charge transport model for polymers, suggesting that the doped PCPDTSBT film has superb charge transport property based on a high crystallinity with olefinic side-chains. This study emphasizes the importance of side-chain engineering by using the sp2-hybridized olefinic substituents to modulate interchain packing, crystalline morphology, and the resulting electrical properties.

Conventional stretchable electronics entailing the adoption of a wavy design, a neutral mechanical plane, and a conformal contact between abiotic and biotic interfaces have shown diverse skin-interfaced applications. Despite such remarkable progress, there have been challenged to be evolved to intelligent skin prosthetics due to the absence of the monolithic integration of neuromorphic constituents into individual sensing and actuating components. Herein, we demonstrate a golden tortoise beetle-inspired stretchable sensory-neuromorphic system comprising an arti cial mechanoreceptor, an arti cial synapse, and an epidermal photonic actuator as three biomimetic functionalities that correspond to a stretchable capacitive pressure sensor, a resistive random-access memory, and a quantum dot light-emitting diode, respectively. This system features a rigid-island structure interconnected with a sinter-free printable conductor (stretchability ~ 160%, conductivity ~ 18,550 S/cm), which allows one to improve both areal density and structural reliability while avoiding the thermal degradation of heat-sensitive stretchable electronic components. Moreover, even in the skin deformation range, the system accurately recognizes various patterned stimuli via an arti cial neural network with training/inferencing functions. Our new bioinspired system is therefore expected to be an important step toward the implementation of intelligent wearable electronics.

We demonstrated modulation of charge carrier densities in all-solution-processed organic field-effect transistors (OFETs) by modifying the injection properties with self-assembled monolayers (SAMs). The all-solution-processed OFETs based on an n-type polymer with inkjet-printed Ag electrodes were fabricated as a test platform, and the injection properties were modified by the SAMs. Two types of SAMs with different dipole direction, thiophenol (TP) and pentafluorobenzene thiol (PFBT) were employed, modifying the work function of the inkjet-printed Ag (4.9 eV) to 4.66 eV and 5.24 eV with TP and PFBT treatments, respectively. The charge carrier densities were controlled by the SAM treatment in both dominant and non-dominant carrier-channel regimes. This work demonstrates that control of the charge carrier densities can be efficiently achieved by modifying the injection property with SAM treatment; thus, this approach can achieve polarity conversion of the OFETs.

In 2019, the device performances of the display technologies were largely advanced by the development of new materials and of the device architecture and driving scheme. The recent progress in the areas of virtual reality (VR), augmented reality (AR), quantum dot light-emitting diode (QLED), and organic light-emitting diode (OLED) is comprehensively summarized and discussed in this paper. ARTICLE HISTORY