Zhenhua Jiang

Flexible, stretchable, wearable, and stable electronic materials are widely studied, owing to their applications in wearable devices and the Internet of Things. Because of the demands for both strain-insensitive resistors and high gauge factor (GF) strain-sensitive materials, anisotropic strain sensitivity has been an important aspect of electronic materials. In addition, the materials should have adjustable strain sensitivities. In this work, such properties are demonstrated in reduced graphene oxide (RGO) with hierarchical oriented wrinkle microstructures, generated using the two-step shrinkage of a rubber substrate. The GF values range from 0.15 to 28.32 at 100% strain. For device demonstrations, macrostructure patterns are designed to prepare patterned wrinkling graphene at rubber substrate (PWG@R). Serpentiform curves can be used for the constant-value resistor, combined with the first-grade wrinkles. Strip lines can increase the strain-sensing property, along with the second-grade wrinkles. The patterned sensor exhibits improved GF values range from 0.05 to 49.5. The assembled sensor shows an excellent stability (>99% retention after 600 cycles) with a high GF (49.5). It can monitor the vital signs of the throat and wrist and sense large motions of fingers. Thus, PWG@R-based strain sensors have great potential in various health or motion monitoring fields.

Graphene‐based aerogels (GAs) have been extensively studied for pressure sensing applications due to their high compressibility and conductivity. But the usually‐adopted high‐temperature treatment generally damages the flexibility and stability. It is still challenging to prepare piezoresistive sensors with a wide linear range, and reliable cyclic performance. Herein, we demonstrate an excellent wide‐range piezoresistive sensor based on an aerogel of methylcellulose reinforced reduced graphene oxide (MC/GA). A steaming reduction at 120 °C is proposed to properly control the intermolecular forces and the chemical bonding between MC and GA. The finite element analysis indicates that wrinkled lamellae with hierarchical pores are beneficial to minimize the stress concentrations. As a result of the combined architecture of reinforced, oriented, and wrinkled lamellae with hierarchical pores, the MC/GA has a superior linearity in a much wide range (0–17 kPa, R² > 0.997), a high sensitivity (9.38 kPa⁻¹), a short response time (99% retention). As demonstrations, the MC/GA sensor can monitor vital signs of the upper lip, throat or wrist, and can sense the large motion of the fingers, elbows, and feet. These advantages make the MC/GA sensor have a great potential in various health monitoring and motion‐detecting fields.

Methylammonium lead triiodide perovskite (CH₃NH₃PbI₃, MAPbI₃) has been emerging as an easy processing and benign defect material for optoelectronic devices. Fiber-like perovskite materials are especially in demand for flexible applications. Here we report on a kind of polyacrylonitrile (PAN)/MAPbI₃ composite fiber, which was electrospun from the mixing solution of PAN and MAPbI₃. The absorption edge and optical gap of the PAN/MAPbI₃ composite fibers can be easily tuned as the ratio of the perovskite changes. Both the moisture stability and the thermal stability of the perovskite are improved with the protection of PAN polymers. Flexible photodetectors based on this perovskite fiber were fabricated and analyzed. The photoresponse of the detector was highly sensitive to broadband visible light, and reached 6.5 μA W⁻¹ at 700 nm with a voltage bias of 10 V. Compared with pure MAPbI₃ photodetectors, this composite fiber photodetector has much-improved stability and flexibility, which can even be used to detect motion-related angular changes.