Research Projects
In the past ten years, I have possessed a strong dedication to organic electronic materials and printed flexible devices. My research expertise covers a wide range of areas, including organic semiconducting materials, polymer conductive composites, printed flexible/stretchable sensors, and flexible hybrid integrated circuits.
I: Printed flexible/stretchable sensor system
Flexible/stretchable sensors are essential for advancing Society 5.0, given their advantages in wearable devices and robotics. I have successfully developed various high-performance flexible/stretchable sensors using functional organic materials and printing electronics technologies. These achievements have sparked novel design strategies for materials and structures of flexible/stretchable sensors and have propelled their real-world applications.
1.1 Printed flexible temperature sensor with excellent humidity stability
Figure 1. (a) Ink component. (b) printed hybrid circuit with sensor. (c) skin temperature monitoring.
In this research, I developed a novel temperature sensing ink based on cross-linked poly(3,4-ethylenedioxythiophene): poly(styrenesulfonate) (PEDOT:PSS), realized a fully printed temperature sensor with excellent humidity stability. Furthermore, the integration of the printed sensor into a printed flexible hybrid circuit has resulted in a wireless temperature sensing platform capable of stable real-time healthcare monitoring.
1.2 Printed stretchable strain sensor with high sensitivity and wide working range.
Figure 2. (a) Printed stretchable strain sensor. (b) Working mechanism. (c) Sensor performances.
There is a trade-off between high sensitivity and a wide working range in resistive stretchable strain sensors. To overcome this challenge, I have developed a novel brittle-stretchable conductive network by screen-printing.This network consists of both brittle and stretchable conductive layers (Figure 4). This innovative conductive network provides superior electrical-mechanical performance to the strain sensors, enabling high sensitivity and a wide working range simultaneously.
1.3 Printed flexible humidity sensor with fast response
Figure 3. (a) Printed humidity sensor. (b) SEM of CNF/CB film. (c) Working mechanism. (d) Response of the sensor to humidity.
Flexible humidity sensors were usually based on complex processes and expensive materials while suffering low sensitivity and slow response. This work developed a high-performance, low-cost printed flexible humidity sensor using a cellulose nanofiber/carbon black (CNF/CB) composite . Benefits from the hydrophilic and porous nature of cellulose nanofiber, the sensor providing high sensitivity and fast response to humidity, and available for human breath monitoring.
1.4 Printed multifunctional mechanical sensors using porous conductive composite
Figure 4. (a) Illustration ink synthesis. (b) Printed sensors. (c) SEM of the porous composite film
Porous conductive network is promising for high-performance flexible mechano-sensors but difficult to achieve by simple method. This work has developed a novel printable composite ink based on a simple mixture of PDMS, carbon black (CB), and a deep eutectic solvent (DES). This unique ink could spontaneously form a porous conductive network without any complex process . In addition, the phase segregation between PDMS and CB contributes to the excellent low hysteresis in the composite. This research provides a straightforward approach to realize high-performance pressure and strain sensors, offering valuable insights for the composite materials design.
1.5 System integration of flexible/stretchable sensors
Figure 5. System integration of flexible printed sensors for practical applications.
In addition to the functional materials development, I also actively pursued the system integration of flexible sensors for practical applications. Notably, the development of a robotic tactile sensor system, wireless healthcare device, and printed hybrid circuit stands as a testament to the achievements. These accomplishments have not only garnered significant attention within academia but have also attracted interest from industry.
II: Liquid crystalline organic semiconductors
The liquid crystalline organic semiconductor shows great promise for a wide range of electronic devices, thanks to its high charge carrier mobility, molecular self-organization, and the ability to intentionally control molecular orientation. During my master course and doctoral course, I have undertaken a systematic investigation of liquid crystals (LCs), uncovering essential factors governing phase behaviors, charge carrier mobility, and molecular orientation in these materials, advancing their applications in innovative organic electronic devices.
Figure 6. Overview of the applicant’s research on liquid crystalline organic semiconductors.
2.1 Systhesis and change transport study of discotic liquid crystalline
Minor modifications in the molecular structures of organic semiconductors can significantly impact their packing structures. Therefore, comprehending the structure-property relationships is crucial. The applicant synthesized a series of discotic liquid crystal dimers as model molecules, and systematically investigated their phase behaviors and charge carrier mobilities. These works establish a clear structure-property relationship in discotic liquid crystals and offer a molecular design strategy for achieving highly ordered liquid crystalline phases and high charge carrier mobility.
2.2 Control molecular orientation of liquid crystalline thin film
Achieving precise control over the molecular orientation of organic semiconductors poses a considerable challenge. By utilizing the surface anchoring effect and the self-assembly nature of liquid crystal materials, the applicant has developed two novel orientation strategies: 1) utilizing a sacrificial re-orientation layer realizing a planarly-oriented organic semiconductor film; 2) constructing a co-planar nanogap electrode as the orientation structure, which facilitated a highly ordered vertically-oriented organic semiconductor film in a 100 nm channel. These works provide efficient approaches to realize highly conductive pathways in organic thin films and open new possibilities for the application of liquid crystalline materials in high-performance organic diodes.
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