The applications of two-dimensional materials in electronics and energy harvesting

Abstract

With the rapid development of the Internet of Things (IoT), people's daily lives are increasingly dependent on diverse personal electronic devices. To meet the demands of portability, seamless integration, and comfort in wearable and implantable systems, these devices must be smaller, more efficient, and mechanically flexible. However, conventional materials such as silicon, metals, and oxides face limitations including large size, heavy weight, poor biocompatibility, and limited adaptability to deformation. Traditional batteries also show low compatibility with flexible systems and raise environmental and safety concerns. These drawbacks restrict next-generation portable and wearable devices, driving research into novel materials. Two-dimensional (2D) materials, such as transition metal dichalcogenides (TMDs) and MXenes, have gained attention due to their unique optical, electrical, and mechanical properties, making them promising for miniaturized and flexible devices. Optical studies of heterostructures composed of monolayer WS2 on MXene quantum dots (QDs) show strong photoluminescence (PL) enhancement at room temperature and rich excitonic dynamics at cryogenic temperatures. These arise from localized plasmonic effects of QDs and the suspended WS2 structure, which enhance many-body interactions and emission efficiency. This demonstrates the potential of 2D materials for high-performance optoelectronic devices. Monolayer WS2, with a direct bandgap of about 2.0 eV and excellent flexibility, is well-suited for wearable optoelectronic applications such as LEDs. Using a hybrid continuous-pulsed injection scheme, WS2 LEDs achieve over 20-fold enhancement in emission efficiency and a large active area (around 25 micronmeter) at room temperature. Moreover, tuning the applied alternating voltage allows emission wavelength modulation over 40 nm, highlighting the potential of 2D materials in high-performance, wavelength-tunable optoelectronics. Beyond optoelectronics, MXene-based systems offer great promise in energy harvesting due to their biocompatibility and conductivity. A MXene (Ti3C2Tx) 5G antenna efficiently harvests radio-frequency energy under very low input power, requiring about 16 times lower power density than copper antennas, while maintaining over 99% efficiency under 90 degrees of bending. This flexibility underscores its potential as a wireless, battery-free energy harvester for wearables. Despite these advantages, MXene antennas face challenges such as relatively high minimum input power and restricted operational ranges. To address this, MXene-based hybrid moisture electric generators (hMEGs) have been developed. hMEGs continuously generate electricity by absorbing ambient moisture, providing a sustainable green power supply. When integrated into textiles via screen printing, planar MXene hMEGs can directly power devices such as hearing aids and Bluetooth-enabled power management systems. In summary, this thesis explores the unique properties of 2D materials, demonstrating their application in flexible optoelectronic devices and energy harvesters. It proposes two types of 2D materials-based generators as sustainable power sources for wearable systems. These results offer valuable insights and guidance for future integration of 2D materials into wearable technologies, both as functional devices and as power supplies. Show more