# Laser-Induced Graphene Film and Its Applications in Flexible Electronics
## 2 Applications of Laser-Induced Graphene in Flexible Electronics
To further improve the electrochemical performance of the micro-supercapacitors, many methods have been employed for enhancing the interactions between the LIG interdigital electrode and electrolyte from both the physical and chemical aspects, such as heteroatom (e.g., nitrogen, boron, phosphorus) doping [16; 17], specific surface area enhancement [18; 19], and surface functional group or microstructure modification [20], etc. For example, our group first developed an ultra-fast ultraviolet laser induction and activation technique for the fabrication of LIG films with the features of hierarchical porous structure, small amount of doped potassium (~0.50 wt%), high surface area (>1300 m\({}^{2}\) g\({}^{-1}\)), and super-hydrophilicity (maximum droplet spreading velocity reaches 424.7 mm s\({}^{-1}\)). The resulting in-plane micro-supercapacitors exhibit an ultrahigh areal capacitance of 128.4 mF cm\({}^{-2}\), which outperforms state-of-the-art laser-processed carbon- based micro-supercapacitors [18]. Moreover, a high-voltage micro-supercapacitors with voltage up to several hundred volts can also be realized through the in-plane or through-plane design of LIG electrode structure, including square electrode arrays [21], linear strip electrode arrays [22], and three-dimensional stacked arrays [23]. Furthermore, the addition of the paper-cut process also helps to improve the tensile properties of micro-supercapacitors [24]. On the other hand, patterned LIG films are also good candidates for light-driven actuators based on the Marangoni effect due to their good photothermal properties, reasonable mechanical strength, and broad-spectrum light absorption properties [25; 26]. In 2020, [PERSON] et al. [25] employed patterned LIG films as stick-on photothermal labels for developing 2D and 3D light-driven actuators. Under light irradiation, the patterned 2D and 3D light-driven actuators can be used for directional movement and translation and rotation motions under the guidance of photothermal Marangoni actuation. Similarly, electrothermally controlled actuators based on patterned LIG films were reported by [PERSON] et al. [27], and its application in mechanically guided 3D assembly and human-soft actuators interaction was explored. The stress caused by the significant thermal expansion can deform strategically designed 2D precursors into programmed 3D architectures. According to the advantages of LIG films over conventional graphene/binder composites, other applications were also developed in recent years through further improving the interface and/or electrically/thermally conductive networks of LIG films, including solid-solid/liquid triboelectric nanogenerators [28; 29], electro-catalysis carriers [30], and Joule heaters [31; 32]. For example, our group developed an in-situ growing LIG process that enables to one-step patterning of superhydrophobic fluorine-doped graphene on fluorinated ethylene propylene-coated polyimide films [29]. This method utilizes the various spectral responses of propylene and polyimide upon laser excitation to preferentially generate an environment for LIG formation, thus eliminating the need for multi-step processes and specific atmospheres (e.g., inert gas). The structured and water-repellant structures provided by the spectral-tuned interfacial LIG process are very suitable for the use as the electrode of a flexible droplet-based electricity generator, showing high power conversion efficiency with a peak power density of 47.5 W m\({}^{-2}\) by releasing a 105 uL of water droplet from a height of 25 cm. All these cases confirm the versatility and advancement of patterned LIG films as functionally integrated electrodes, developing flexible electronics with improved electrical/thermal/electrochemical/triboelectric behavior and new functionalities, which can be used in various wearable electronics for the coming Internet of Things in the near future.