Wearable electronic medical devices measuring continuous biological signals for early disease diagnosis should be small and lightweight for consecutive usability. As a result, there has been an increasing need for new energy supply systems that provide continuous power without any interruption to the operation of the medical devices associated with the use of conventional batteries. In this work, we developed a patch-type self-charging supercapacitor that can measure biological signals with a continuous energy supply without batteries. The glucose oxidase coated on the surface of the microneedle-type glucose sensor encounters glucose in the interstitial fluids of the human body. Electrons created by glucose oxidation operate the self-powered system in which charging begins with the generation of potential differences in supercapacitor electrodes. In an 11 mM glucose solution, the self-powered solid-state supercapacitors (SPSCs) showed a power density of 0.62 mW/cm2, which resulted in self-charging of the supercapacitor. The power density produced by each SPSC with a drop of 11 mM glucose solution was higher than that produced by glucose-based biofuel cells. Consequently, the all-in-one self-powered glucose sensor, with the aid of an Arduino Uno board and appropriate programming, effectively distinguished normal, prediabetic, and diabetic levels from 0.5 mL of solutions absorbed in a laboratory skin model.

Intrinsically stretchable light-emitting diodes (LEDs) will be critical components in future stretchable electronics. However, limited research has been conducted on stretchable electroluminescent (EL) layers for LED devices. Blending conjugated polymers (CPs) with an elastomer has been a simple and effective method enabling widespread use of stretchable polymer semiconductors in stretchable field-effect transistors (FETs). In this study, we adopted the concept of blending elastomers into CPs for use in stretchable polymer LEDs (PLEDs). By blending light-emitting polymers prepared from polyphenylenevinylene (PPV) derivatives with thermoplastic polystyrene-block-polybutadiene-block-polystyrene (SBS) elastomers, a stretchable emission layer (EML) was fabricated, and its mechanical, electrical, and morphological properties were studied. The blended film was stretched up to 60% before vertical cracking occurred, and it maintained its pristine electrical properties. Finally, stretchable PLEDs were fabricated with the use of stretchable EMLs, and this showed that 50% of the maximum luminance was maintained upon stretching up to 60%.

A photoluminescence mapping image of monolayer (1L) MoS2 clearly shows the difference in PL intensity at the boundary between bare SiO2 and plasma-treated SiO2 (3 min).

Intrinsically stretchable organic light-emitting diodes (is-OLEDs) have attracted significant attention for use in next-generation displays. However, most studies conducted to date have focused on how to make fluorescent materials stretchable, utilizing singlet excitons with a theoretical internal quantum efficiency (IQE) of 25%. Although phosphorescent materials have a high theoretical IQE of 100%, no previous work has attempted to develop stretchable phosphorescent light-emitting materials. In this work, we designed a solution-processable and intrinsically stretchable phosphorescent light-emitting layer (isp-EML) by blending various additives together with a mixture of a polymer host, poly­(9-vinyl carbazole) (PVK), and a small-molecule emitting dopant, tris­(2-phenylpyridine)­iridium­(III) (Ir­(ppy)3). The poly­(ethylene glycol)-block-poly­(propylene glycol)-block-poly­(ethylene glycol) (PEG–PPG–PEG) additive significantly improved the stretchability (∼100% strain), brightness (∼5400 cd/m2), and efficiency (∼25.3 cd/A) of the isp-EML compared with a conventional phosphorescent EML (approximately 3% strain, 3750 cd/m2, and 12.1 cd/A). Furthermore, by changing the emitting dopant in the isp-EML, we could control the red, green, and blue emission colors, with increasing mechanical and electrical properties of the isp-EML. These results highlight the promising potential of the novel blend system using phosphorescent materials and additives for application in highly stretchable and efficient OLEDs.

Since the skin is the most efficient system for tactile sensing, many studies have emulated the sensing mechanism of the skin. [20][21][22][23] As shown in Figure 1a, skin distinguishes different pressures by four mechanoreceptors (Merkel disk, Ruffini corpuscle, Meissner corpuscle, and Pacinian corpuscle), [24,25] which can be categorized into two types: slow adapting (SA) mechanoreceptors and fast adapting (FA) mechanoreceptors. [26] Since SA mechanoreceptors (Merkel disk, Ruffini corpuscle) produce signals in response to the state of pressure, they are appropriate to sense static pressure. [27] On the other hand, FA mechanoreceptors (Meissner corpuscle, Pacinian corpuscle) produce a signal only at a sudden change of pressure, which is appropriate to detect dynamic pressure. [26] In the case of an artificial tactile sensor, there are four main transduction mechanisms to sense pressure: piezoresistive, capacitive, piezoelectric, and triboelectric mechanisms. [28][29][30][31] Among them, piezoresistive-and capacitive-type sensors are useful for SA signal detection, and piezoelectric-and triboelectric-type sensors are suitable for FA signal detection. [32,33] Ha et al. demonstrated an e-skin that detected both static and dynamic tactile stimuli by piezoresistive and piezoelectric sensors. [34] Hierarchically structured ZnO nanowire arrays were interlocked for efficient deformation and variation of the contact area, which enabled high sensitivity. With the interlocked wires, high sensitivity (6.8 kPa -1 ) for static pressure could be accomplished with an ultrafast response time (5 ms) in the piezoresistive mode, and 250 Hz of high-frequency vibration could be detected by the piezoelectric mode. Chun et al. fabricated a self-powered mechanoreceptor sensor that distinguished the functions of FA and SA through a piezoelectric transduction mechanism and ionics. [35] By combining the piezoelectric film and ion channel, FA and SA signals could be measured simultaneously, which made it possible to interpret complex tactile stimuli. Here, when different types of output (resistance, capacitance, voltage, or current) are involved in discerning the FA and SA signal, [36][37][38][39][40] various measuring apparatuses or signal converters for processing data are needed for processing multiple data. Consequently, the integrated system becomes too bulky and high-power-consuming, which is not suitable for e-skin technology. [41] Constructing a single-mode sensor, which produces a single type of output in response to both FA and the SA stimuli, may A piezoelectric tactile sensor is beneficial for creating a self-powered system with a compact design, which is essential in electronic-skin technology. However, piezoelectricity is only capable of dynamic pressure detection because it responds to sudden environmental changes. Since it is common to add another sensing unit to detect static pressure that accompanies bulkiness, including a measuring apparatus, we demonstrate a self-powered, singlemode piezoelectric tactile sensor by fabric...

With the evolution of semiconducting industries, thermomechanical failure induced in a multilayered structure with a high aspect ratio during manufacturing and operation has become one of the critical reliability issues. In this work, the effect of thermomechanical stress on the failure of multilayered thin films on Si substrates was studied using analytical calculations and various thermomechanical tests. The residual stress induced during material processing was calculated based on plate bending theory. The calculations enabled the prediction of the weakest region of failure in the thin films. To verify our prediction, additional thermomechanical stress was applied to induce cracking and interfacial delamination by various tests. We assumed that, when accumulated thermomechanical-residual and externally applied mechanical stress becomes larger than a critical value the thin-film cracking or interfacial delamination will occur. The test results agreed well with the prediction based on the analytical calculation in that the film with maximum tensile residual stress is the most vulnerable to failure. These results will provide useful analytical and experimental prediction tools for the failure of multilayered thin films in the device design stage.

Perovskite Light‐Emitting Diodes In the ambient air, a novel N2 gas blowing step is applied during spin‐coating of the precursor solution to obtain uniform methylammonium lead bromide (MAPbBr3) perovskite nanocrystal films with fewer surface and interfacial defects than solution‐processed perovskite films. Furthermore, PEI‐ and PFN‐doped TPBi acted as passivation agents between the rough surface of the perovskite film and the electron transport layer. Consequently, the high surface work function of PEI‐ and PFN‐doped TPBi resulted in the reduced and balanced injection of electrons in the perovskite light‐emission layer (EML) of the PeLEDs, producing a higher luminance, also showed a longer lifetime. More details can be found in article number http://doi.wiley.com/10.1002/pssa.201900426 by Taejun Kim, Jin‐Woo Park and co‐workers.

Conformal contact with skin is a critical requirement for wearable electronics in medical healthcare, artificial electronics, and human–computer interfaces. Tattoo‐like electronics exploiting water‐dissolvable polymers have been introduced to directly transfer electronics to the skin increasing conformality and adhesion. However, water‐dissolvable polymers cannot be anchored on the skin while maintaining electrical properties because water‐based sweat can destroy the polymer substrate. In this study, we present a transparent and skin‐attachable electrode (TSE) composed of highly conductive silver nanowires and biocompatible polyurethane composite using surface redissolution by ethanol. The TSE can be fabricated into various patterns by a simple fabrication method and firmly mounted on the skin. There was no reddishness or residue on the attached spot after detachment. Additionally, the TSE showed low mechanical modulus of 225 kPa and an optical transmittance of ≈70% at 550 nm. Stable and conformal contact with the skin leads to effective body motion sensing and sensitive electrophysiological signal acquisition due to the low electrical interfacial impedance.