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This paper presents a novel flexible capacitive 3D tactile sensor using cross-bar polydimethylsiloxane (PDMS) walls and micropillar arrays as the composite structure dielectric layer. The tactile sensor unit consists of a $2\times 2$ capacitor array where electrode pairs are arranged in a cross-bar pattern to ensure a fixed overlap area for these capacitors. A top bump is introduced for the sensor to ensure the force is applied uniformly on the sensor. When a force is applied on the sensor, it changes the capacitances of the four capacitors, distinguishing the forces from different directions. The sensitivities of the sensor in the x-, y- and z- directions are 95.08%/N, 98.30%/N and 237.48%/N, in the ranges of 0-0.15 N, 0-0.15 N and 0-0.1 N respectively, much better than most of reported ones. The high sensitivities of the proposed sensor unit are attributed to the composite structure dielectric layer and the optimized Young’s modulus of PDMS. The flexible capacitive tactile sensor shows great potential for applications in robot technology.

Inkjet-printed photodetectors have gained enormous attention over the past decade. However, device performance is limited without postprocessing, such as annealing and UV exposure. In addition, it is difficult to manipulate the surface morphology of the printed film using an inkjet printer because of the limited options of low viscosity ink solutions. Here, we employ a concept involving the control of the inkjet-printed film morphology via modulation of cosolvent vapor pressure and surface tension for the creation of a high-performance ZnO-based photodetector on a flexible substrate. The solvent boiling point across different cosolvent systems is found to affect the film morphology, which results in not only distinct photoresponse time but also photodetectivity. ZnO-based photodetectors were printed using different solvents, which display a fast photoresponse in low-boiling point solvents because of the low carbon residue and larger photodetectivity in high-boiling point solvent systems due to the porous structure. The porous structure is obtained using both gas–liquid surface tension differences and solid–liquid surface differences, and the size of porosity is modulated from nanosize to microsize depending on the ratio between two solvents or two nanomaterials. Moreover, the conductive nature of graphene enhances the transport behavior of the photocarrier, which enables a high-performance photodetector with high photoresponsivity (7.5 × 102AW–1) and fast photoresponse (0.18 s) to be achieved without the use of high-boiling point solvents.

sQuantum dot light-emitting diodes (QD-LEDs) are considered as competitive candidate for next-generation displays or lightings. Recent advances in the synthesis of core/shell quantum dots (QDs) and tailoring procedures for achieving their high quantum yield have facilitated the emergence of high-performance QD-LEDs. Meanwhile, the charge-carrier dynamics in QD-LED devices, which constitutes the remaining core research area for further improvement of QD-LEDs, is, however, poorly understood yet. Here, we propose a charge transport model in which the charge-carrier dynamics in QD-LEDs are comprehensively described by computer simulations. The charge-carrier injection is modelled by the carrier-capturing process, while the effect of electric fields at their interfaces is considered. The simulated electro-optical characteristics of QD-LEDs, such as the luminance, current density and external quantum efficiency (EQE) curves with varying voltages, show excellent agreement with experiments. Therefore, our computational method proposed here provides a useful means for designing and optimising high-performance QD-LED devices.

Quantum dot light-emitting diodes (QD-LEDs) are widely recognised as great alternatives to organic light-emitting diodes (OLEDs) due to their enhanced performances. This focus article surveys the current progress on the state-of-the-art QD-LED technology including material synthesis, device optimization and innovative fabrication processes. A discussion on the material synthesis of core nanocrystals, shell layers and surface-binding ligands is presented for high photoluminescence quantum yield (PLQY) quantum dots (QDs) using heavy-metal free materials. The operational principles of several types of QD-LED device architectures are also covered, and the recent evolution of device engineering technologies is investigated. By exploring the fabrication process for pixel-patterning of QD-LEDs on an active-matrix backplane for full-colour display applications, we anticipate further improvement in device performance for the commercialisation of next-generation displays.

Perovskite quantum dots (PeQDs) have been developed rapidly as photoactive materials in hybrid phototransistors because of their strong light absorption, broad bandgap customizability, and defect-tolerance in charge-transport properties. The solvent treatment has been well recognized as a practical approach for improving the charge transport of PeQDs and the photoresponsivity of PeQD phototransistors. However, there is a lack of fundamental understanding of the origin of its impacts on the material’s ambient stability as well as phototransistor’s operational lifetime. Especially, the relationship between surface ligands dissociation and their microstructural reconstruction has not been fully elucidated so far. Herein, we report that a simultaneous enhancement of photoresponsivity and ambient tolerance for PeQD-based hybrid phototransistors can be realized via medium-polarity-solvent treatment on solid-state PeQDs. Our comprehensive optoelectronic characterization and electron microscopic study reveals that the crystal morphology, instead of surface ligands, is the dominating factor that results in the PeQD’s stability enhancement associated with the preservation of optical property and quantum confinement. Besides, we unveil a marginal reconstruction process occurred during solvent treatment, which opens up a new route for facets-oriented attachment of PeQDs along the zone axis to suppress the damage from water molecules penetration. Our study yields a new understanding of the solvent impact on PeQD microstructures reconstruction and suggests new routes for perovskite materials and corresponding device operational stability enhancement.

Flexible capacitors are a promising power source for foldable and biological electronic devices. Although various materials and device structures have been explored, they are still limited by low energy densities and slow rate capabilities compared to their rigid counterparts. Here, asymmetric carbon nanohorns are proposed as an active material to fabricate flexible solid-state carbon wire (CW)-based electrochemical supercapacitors (ss-CWECs) which exhibit high power density and ultra-low cutoff frequency. By controlling the electric arc reaction at low temperature (77 K), asymmetric single-wall carbon nanohorns (SWCNHs) have been synthesised with high yield. Based on microscopy and electrochemical characterisation, the fundamental reaction mechanism in polyvinyl-based electrolyte system has been elucidated, as being associated with deprotonation reaction at acid, base and elevated temperature conditions. Additionally, by using activated carbon, multi-walled carbon nanotubes and SWCNHs as hybrid electrode materials (5:1:1), remarkable specific length capacitance of 48.76 mFcm-1 and charge-discharge stability (over 2000 times cycles) of ss-CWECs have been demonstrated, which is the highest reported to date. Furthermore, a highpass filter for eliminating ultra-low electronic noise has been demonstrated, which enables an optical Morse Code communication system to be operated. Current results confirm the SWCNHs as promising materials for high-performance soft electronics and energy storage applications.

We report on the design, fabrication, and characterization of heterostructure In-Zn-O (IZO) thin-film transistors (TFTs) with improved performance characteristics and robust operation. The heterostructure layer is fabricated by stacking a solution-processed IZO film on top of a buffer layer, which is deposited previously using an electron beam (e-beam) evaporator. A thin buffer layer at the dielectric interface can help to template the structure of the channel. The control of the precursors and of the solvent used during the sol-gel process can help lower the temperature needed for the sol-gel condensation reaction to proceed cleanly. This boosts the overall performance of the device with a significantly reduced subthreshold swing, a four-fold mobility increase, and a two-order of magnitude larger on/off ratio. Atomistic simulations of the a-IZO structure using molecular dynamics (both classical and ab initio) and hybrid density functional theory (DFT) calculations of the electronic structure reveal the potential atomic origin of these effects.

In this paper, partial density of states and band structures of Anatase's (001) and (101) facets were studied by first-principles calculation. Based on partial density of states, electrons in the (001) facet of Anatase have much higher transition probability to be excited from valence band maximum to conduction band minimum compared with those in an (101) facet, which shows a stronger electronic activity of (001) facet. Besides, the (001) and (101) facets of Anatase have a direct and indirect band structure, respectively, based on the first-principle calculation results. The direct band structure of the (001) facet makes it more suitable to be used in optical detection. Anatase TiO2 nanotubes array modified with (001) exposed nanofacets were grown on Ti substrates by anodization, hydrothermal, and then post annealing. An ultrahigh responsivity as high as 1575.97μA/mW·cm2 under 365 nm ultraviolet light wavelength and 5 V bias was achieved.

Surface electrical properties is of great significance for developing high-performance organic-inorganic hybrid perovskite based electronic devices. The photovoltage-induced ions transport and redistribution at the surface region have been well studied, but their contributions to the surface electrical properties are still lack of experimental evidences. In this article, a self-powered polymer-based contact electrification probe (PCE-probe) is proposed to investigate the photovoltage- or applied bias-induced ion transport polarization (PI) and ferroelectric polarization (PF) inside the methylammonium lead iodide films (MAPI). Results show that both the PI- and PF-induced ion transport and redistribution create a similar local ion-doping region near the surface. Positive or negative ion-doping produces a n-type or p-type layer, which enhances the interficial junction inside MAPI-based solar cells and benefits the seperation and transfer of photogenerated carriers or excitons. The PI and PF effects can be added up or subtracted from each other depending on the polarization configuration. A qualitative relationship between the PCE-probe output and CE-effect, PI- and PF-induced transferred surface charges is investigated. These results can help to understand the polarization nature inside and the high power conversion efficiency of MAPI-based photovoltaic devices, and provide a feasible analysis method of PCE-probe for detecting surface electrical properties.

A simulation model of electrical percolation through a three-dimensional network of curved CNTs is developed in order to analyze the electromechanical properties of a highly stretchable fiber strain sensor made of a CNT/polymer composite. Rigid-body movement of the curved CNTs within the polymer matrix is described analytically. Random arrangements of CNTs within the composite are generated by a Monte-Carlo simulation method and a union-find algorithm is utilized to investigate the network percolation. Consequently, the strain-induced resistance change curves are obtained in a wide strain range of the composite. In order to compare our model with experimental results, two CNT/polymer composite fibers were fabricated and tested as strain sensors. Their effective CNT volume fractions are estimated by comparing the experimental data with our simulation model. The results confirm that the proposed simulation model reproduces well the experimental data and is useful for predicting and optimizing the electromechanical characteristics of highly stretchable fiber strain sensors based on CNT/polymer composites.

Atomic layer deposited (ALD) ultra-thin alumina film is proposed to control the operational lifetimes of fully biodegradable (FB-) surface sensitive surface acoustic wave (SAW) devices. SAW devices encapsulated with conventional thick organic materials fail to function effectively, while devices with an ultra-thin alumina encapsulation layer (AEL) function normally with high performance. After being subjected to degradation in water, a FB-SAW device with no AEL starts to degrade immediately and fails within 8 h, due to dissolution of the tungsten electrode and piezoelectric material (ZnO). The coating of an ultra-thin AEL on the surfaces prevents SAW devices from undergoing degradation in water and enables SAW devices to perform normally before the AEL is dissolved. The stable operation lifetimes of SAW devices are linearly dependent on the AEL thickness, thus allowing for the design of devices with precisely controlled operational lifetimes and degradation times. The results show that all the materials used could be degraded; also, in vitro cytotoxicity tests indicate that the encapsulated FB-SAW devices are biocompatible, and cells can adhere and proliferate on them normally, demonstrating great potential for broader biodegradable electronic device applications.

The development of flexible displays for wearable electronics applications has created demand for high-performance quantum dot (QD) light-emitting diodes (QLEDs) based on QD core@shell structures. Emerging indium phosphide (InP)-based core@shell QDs show promise as lighting material in the field of optoelectronics because they are environmentally friendly material, can be produced in a cost-effective manner, and are capable of tunable emission. While efforts have been made to enhance the performance of InP-based QLED, the stabilities of InP@ZnSeS QDs film and InP@ZnSeS-based QLED in water/air are not yet fully understood, limiting their practical applications. Herein, a highly durable, flexible InP@ZnSeS QLED encapsulated in an ultrathin film of CYTOP, a solution-based amorphous fluoropolymer, is demonstrated. The CYTOP-encapsulated green flexible QLED shows an external quantum efficiency (EQE) of 0.904% and a high luminescence of 1593 cd/m2 as well as outstanding waterproof performance. The flexible device emits strong luminescence after being immersed in water for ~20 minutes. Even when subjected to continuous tensile stress with a 5 mm bending radius, the high luminescence is preserved. This waterproof architecture can be a promising strategy for wearable electronics applications.

Two ultra-compact silicon bandpass filters are proposed and partly experimentally presented. Both of them have wide bandwidth tunability. Based on the first filter (filter-I), the second filter (filter-II) was designed and has large Free Spectrum Range (FSR). Two filters share the same architecture (matrix architecture), consisting two groups of micro-ring resonator-cascade structures (simply called as micro-ring resonator in this letter). Using this matrix architecture, a wide bandwidth tunability from 75 to 300 GHz can be achieved in filter-I. Based on matrix architecture, double micro-ring resonator (MRR) were adopted and Vernier effect was used in design. It is showed both in simulation and experiment that the FSR of filter-II exceeded 35 nm (around 40 nm in simulation), which is much larger than the FSR of single MRR. Filter-II’s tunability of center wavelength in simulation covers most wavelength from 1530 to 1570 nm. The comparison of bandwidth tunability between filter-I and II reveals that adding paths in matrix architecture may be more effective than adopting high-order micro-ring resonators.

Indium gallium zinc oxide (IGZO) thin‐film transistors (TFTs) are primary components in active integrated electronics, such as displays and sensor arrays, which heavily involve high‐throughput passivation techniques during multilayer fabrication processes. Though oxide compound semiconductors are commonly used for providing uniform and robust passivation, it usually causes performance degradation on IGZO TFTs during passivation process. Herein, a parylene‐C and aluminum oxide (AlOx) hybrid passivation approach are introduced to reduce the damage during AlOx atomic layer deposition (ALD), which results in high‐performance depletion‐mode IGZO TFT to be fabricated on polyethylene naphthalate (PEN) substrate with enhanced bias stability. Compared with parylene‐C passivation, the hybrid‐passivated IGZO TFTs exhibit excellent saturation mobility (7.9 cm2 (V s)−1), ON/OFF ratio (107), hysteresis window (0.73 V), and bias stability (1.44 and −0.27 V threshold voltage shift, Vds = 20 V). Based on systematic Mott–Schottky and X‐ray diffraction characterizations, it is found that TFT performance enhancement is originated from their doping density variation that resulted from a parylene‐C/ALD‐AlOx microstructural hybridization. Finally, this method is implemented to wafer‐scale integrated circuits with high uniformity and a flexible 10 × 10 IGZO TFT backplane matrix on a PEN substrate (2.5 cm × 2.5 cm).

Electronic properties of cubic boron nitride (c-BN) doped with group IIA elements were systematically investigated using the first principle calculation based on density functional theory. The electronic bandgap of c-BN was found to be narrowed when the impurity atom substituted either the B (IIA→B) or the N (IIA→N) atom. For IIA→B, a shallow accept level degenerated into valence band (VB); while for IIA→N, a shallow donor level degenerated conduction band (CB). In the cases of IIBe→N and IIMg→N, deep donor levels were also induced. Moreover, a zigzag bandgap narrowing pattern was found, which is in consistent with the variation pattern of dopants’ radius of electron occupied outer s-orbital. From the view of formation energy, the substitution of B atom under N-rich conditions and the substitution of N atom under B-rich conditions were energetically favored. Our simulation results suggested that Mg and Ca are good candidates for p-type dopants, and Ca is the best candidate for n-type dopant.