All-Ti3C2TxMXene Based Flexible On-chip Microsupercapacitor Array

MXene based flexible photodetectors: progress, challenges, and opportunities

The growing interest in applying 2D transition-metal carbides and nitrides (MXenes) to diverse application fields such as energy storage and harvesters, catalysts, sensors, optoelectronics, electromagnetic interference shielding and antennas since its first discovery in 2011 is clearly evident. Their intrinsic high conductivity limits the development of MXenes in photodetectors that rely on the semiconducting properties of active materials, while the abundant functional groups on the surface of MXenes provide opportunities for using MXenes as sensing materials in the fabrication of flexible photodetectors. Considerable studies on MXene based photodetectors have been carried out, but the main obstacles include seeking novel semiconducting materials in MXene families, the manufacturing technology, etc. This review highlights the progress, challenges and opportunities in MXene based flexible photodetectors and discusses novel materials, architectures, and approaches that capitalize on our growing understanding of MXenes.

Air-Stable Flexible Photodetector Based on MXene-Cs3Bi2I9 Microplate Schottky Junctions for Weak-Light Detection

Weak-light detection technology is widely used in various fields, including industry, high-energy physics, precision analysis, and reflection imaging. Metal-semiconductor-metal (MSM) photodetectors demonstrate high detectivity and high response speed and are one of the suitable structures for the preparation of weak-light detectors. However, traditional MSM photodetectors tend to exhibit high dark currents, which are not conducive to performance improvement. Here, a MXene-Cs₃Bi₂I₉-MXene weak-light detector is proposed. Based on the MXene-Cs₃Bi₂I₉ Schottky junctions, the dark current is reduced by 2 orders of magnitude and the responsivity is significantly improved compared with the traditional Cr/Au-Cs₃Bi₂I₉-Cr/Au MSM photodetector. The device demonstrates excellent photodetection capacity with a photoresponsivity of 6.45 A W^-1, a specific detectivity of 9.45 × 10¹¹ Jones, and a fast response speed of 0.27/2.32 ms. Especially, the device yielded a superior weak-light detectable limit of 10.66 nW cm^-2 and demonstrated excellent optical communication capability. Moreover, such a flexible device shows little degradation in photodetection performance after extreme bending for 4500 cycles, proving remarkable bending endurance and flexibility. The obtained results highlight the great potential of such Cs₃Bi₂I₉/MXene devices as a stable and environmentally friendly candidate for weak-light detection.

Continuous Fabrication of Ti3C2Tx MXene-Based Braided Coaxial Zinc-Ion Hybrid Supercapacitors with Improved Performance

Ti₃C₂T_x MXene-based coaxial zinc-ion hybrid fiber supercapacitors (FSCs) were fabricated with braided structure, which can be prepared continuously and present excellent flexibility and ultrastability. A sports watch driven by the watch belts which weaved uses the obtained zinc-ion hybrid FSC and LED arrays lighted by the FSCs under embedding into textiles, demonstrating the great potential application in smart wearable textiles. Zinc-ion hybrid fiber supercapacitors (FSCs) are promising energy storages for wearable electronics owing to their high energy density, good flexibility, and weavability. However, it is still a critical challenge to optimize the structure of the designed FSC to improve energy density and realize the continuous fabrication of super-long FSCs. Herein, we propose a braided coaxial zinc-ion hybrid FSC with several meters of Ti₃C₂T_x MXene cathode as core electrodes, and shell zinc fiber anode was braided on the surface of the Ti₃C₂T_x MXene fibers across the solid electrolytes. According to the simulated results using ANSYS Maxwell software, the braided structures revealed a higher capacitance compared to the spring-like structures. The resulting FSCs exhibited a high areal capacitance of 214 mF cm^-2, the energy density of 42.8 μWh cm^-2 at 5 mV s^-1, and excellent cycling stability with 83.58% capacity retention after 5000 cycles. The coaxial FSC was tied several kinds of knots, proving a shape-controllable fiber energy storage. Furthermore, the knitted FSC showed superior stability and weavability, which can be woven into watch belts or embedded into textiles to power smart watches and LED arrays for a few days.

Progress and Perspectives in Designing Flexible Microsupercapacitors

Miniaturized flexible microsupercapacitors (MSCs) that can be integrated into self-powered sensing systems, detecting networks, and implantable devices have shown great potential to perfect the stand-alone functional units owing to the robust security, continuously improved energy density, inherence high power density, and long service life. This review summarizes the recent progress made in the development of flexible MSCs and their application in integrated wearable electronics. To meet requirements for the scalable fabrication, minimization design, and easy integration of the flexible MSC, the typical assembled technologies consist of ink printing, photolithography, screen printing, laser etching, etc., are provided. Then the guidelines regarding the electrochemical performance improvement of the flexible MSC by materials design, devices construction, and electrolyte optimization are considered. The integrated prototypes of flexible MSC-powered systems, such as self-driven photodetection systems, wearable sweat monitoring units are also discussed. Finally, the future challenges and perspectives of flexible MSC are envisioned.

In-Situ Annealed Ti3C2Tx MXene Based All-Solid-State Flexible Zn-Ion Hybrid Micro Supercapacitor Array with Enhanced Stability

Zn-ion hybrid supercapacitors (SCs) are considered as promising energy storage owing to their high energy density compared to traditional SCs. How to realize the miniaturization, patterning, and flexibility of the Zn-ion SCs without affecting the electrochemical performances has special meanings for expanding their applications in wearable integrated electronics. Ti₃C₂T_x cathode with outstanding conductivity, unique lamellar structure and good mechanical flexibility has been demonstrated tremendous potential in the design of Zn-ion SCs, but achieving long cycling stability and high rate stability is still big challenges. Here, we proposed a facile laser writing approach to fabricate patterned Ti₃C₂T_x-based Zn-ion micro-supercapacitors (MSCs), followed by the in-situ anneal treatment of the assembled MSCs to improve the long-term stability, which exhibits 80% of the capacitance retention even after 50,000 charge/discharge cycles and superior rate stability. The influence of the cathode thickness on the electrochemical performance of the MSCs is also studied. When the thickness reaches 0.851 µm the maximum areal capacitance of 72.02 mF cm^-2 at scan rate of 10 mV s^-1, which is 1.77 times higher than that with a thickness of 0.329 µm (35.6 mF cm^-2). Moreover, the fabricated Ti₃C₂T_x based Zn-ion MSCs have excellent flexibility, a digital timer can be driven by the single device even under bending state, a flexible LED displayer of "TiC" logo also can be easily lighted by the MSC arrays under twisting, crimping, and winding conditions, demonstrating the scalable fabrication and application of the fabricated MSCs in portable electronics.