Conductive hydrogels as flexible electronic devices, not only have unique attractions but also meet the basic need of mechanical flexibility and intelligent sensing. How to endow anisotropy and a wide application temperature range for traditional homogeneous conductive hydrogels and flexible sensors is still a challenge. Herein, a directional freezing method is used to prepare anisotropic MXene conductive hydrogels that are inspired by ordered structures of muscles. Due to the anisotropy of MXene conductive hydrogels, the mechanical properties and electrical conductivity are enhanced in specific directions. The hydrogels have a wide temperature resistance range of −36 to 25 °C through solvent substitution. Thus, the muscle-inspired MXene conductive hydrogels with anisotropy and low-temperature resistance can be used as wearable flexible sensors. The sensing signals are further displayed on the mobile phone as images through wireless technology, and images will change with the collected signals to achieve motion detection. Multiple flexible sensors are also assembled into a 3D sensor array for detecting the magnitude and spatial distribution of forces or strains. The MXene conductive hydrogels with ordered orientation and anisotropy are promising for flexible sensors, which have broad application prospects in human-machine interface compatibility and medical monitoring.

Conductive hydrogels had demonstrated significant prospect in the field of wearable devices. However, hydrogels suffer from a huge limitation of freezing when the temperature falls below zero. Here, a novel conductive organohydrogel was developed by introducing polyelectrolytes and glycerol into hydrogels. The gel exhibited excellent elongation, self-healing, and self-adhesive performance for various materials. Moreover, the gel could withstand a low temperature of −20 °C for 24 h without freezing and still maintain good conductivity and self-healing properties. As a result, the sample could be applied for motion detection and signal transmission. For example, it can respond to finger movements and transmit network signals like network cables. Therefore, it was envisioned that the effective design strategy for conductive organohydrogels with antifreezing, toughness, self-healing, and self-adhesive properties would provide wide applications of flexible wearable devices.

Flexible hydrogel-based sensors have attracted significant attention due to promising applications of wearable devices.

Transparent ferroelectrics, with promising prospects in transparent optoelectronic devices, have unique advantages in self-powered photodetection. The self-powered photodetectors based on the photovoltaic effect have quicker responses and higher stability compared with those based on the pyroelectric effect. However, the ferroelectric ceramics previously applied are always opaque and have no infrared light-stimulated photovoltaic effect. Thus, it would be very meaningful to design photodetectors based on infrared light-stimulated photovoltaic effect and/or transparent ferroelectric ceramics. In this work, highly optical transparent pristine lead lanthanum zirconate titanate (PLZT) and band gap-engineered Ni-doped PLZT ceramics with excellent piezoelectric/ferroelectric properties were prepared by hot-pressing sintering. Stable and excellent photovoltaic performance was obtained for pristine PLZT and band gap-engineered PLZT. The value of short-circuit current density is at least 2 orders of magnitude larger than those in PLZT reported in previous works. The transparent PLZT and Ni-doped PLZT ferroelectric ceramics are applied as self-powered photodetectors for the first time for 405 nm and near-infrared light, respectively. The devices based on PLZT under 405 nm light exhibit high detectivity (7.15 × 10 7 Jones) and quick response (9.5 ms for rise and 11.5 ms for decay), and those devices based on Ni-doped PLZT, under near-infrared light filtered from AM 1.5 G simulated sunlight, also exhibit high detectivity (6.86 × 10 7 Jones) and short response time (8.5 ms), both presenting great potential for future transparent photodetectors.

Conductive hydrogels have recently gained impressive attention in biological medicine and intelligent electronics. Despite the multifunctions demonstrated by existing conductive hydrogels, it is still a challenge to introduce a hydrogel to adjust the distance between the peritumoral organs and the tumor, reducing the radiation damage to the peritumoral organs. Here, a hydrophobic associating hydrogel with multiple desirable features is fabricated based on diverse supramolecular assembly. The introduction of MXene and hydrolyzed keratin (HK) imparts the hydrogel with excellent conductivity, ultra‐stretchability (>2000%), and good self‐adhesion. Moreover, the hydrogel is utilized as an intelligent sensor intended for monitoring various human movements and physiological signals, demonstrating a wide strain window, the rapid response time (130 ms), and outstanding strain sensitivity (GF = 10.22). Inspired by balloon inflation, the hydrogel is designed to separate the tumor from the peritumoral organs in brachytherapy. It plays a role in reducing the radiation dose and damage to the peritumoral organs. The authors also simulate the attenuation process of the radiation signal according to the change of the hydrogel size and develop a smartphone application (app) to monitor the safety range of the different radiation risks, manifesting its great potential in soft intelligent sensors.

Traditional optoelectronic devices without stretchable performance could be limited for substrates with irregular shape. Therefore, it is urgent to explore a new generation of flexible, stretchable, and low-cost intelligent vehicles as visual display and storage devices, such as hydrogels. In the investigation, a novel photochromic hydrogel was developed by introducing the negatively charged ammonium molybdate as a photochromic unit into polyacrylamide via ionic and covalent cross-linking. The hydrogel exhibited excellent properties of low cost, easy preparation, stretchable deformation, fatigue resistance, high transparency, and second-order response to external signals. Moreover, the photochromic and fading process of hydrogels could be precisely controlled and repeated under the irradiation of UV light and exposure of oxygen at different time and temperature. The photochromic hydrogel could be considered applied for artificial intelligence system, wearable healthcare device, and flexible memory device. Therefore, the strategy for designing a soft photochromic material would open a new direction to manufacture flexible and stretchable devices.

No abstract

Trap-state passivation has been validated to efficiently improve the performance of perovskite solar cells. Small volatile molecules and polymers both have the ability to reduce the trap states in perovskite. Herein, we demonstrate the feasibility of passivation by nonvolatile small molecules with carboxylic acid groups such as benzoic acid, p-phthalic acid, and trimesic acid. They can obviously increase the fill factor of the photocurrent density–voltage curves. Furthermore, the relationship between the molecular structure and passivation effect is proposed by fixing the concentration of carboxylic acid groups. Trimesic-acid-doped perovskite solar cells significantly increase the power conversion efficiency from 12.52 ± 0.67 to 14.51 ± 0.81 (champion efficiency, 15.81%) under standard AM 1.5G illumination. Our work expands the chemical additives in perovskite and further demonstrates how the additive molecular structure influences the performance of solar cells.