The research team of Professor Ju Byeong Kwon has high expectations for the application of a flexible and transparent biodegradable organic phototransistor to wearable devices, especially for the development of biomedical material.

▲ Professor Ju Byeong Kwon, Department of Electrical and Electronic Engineering, College of Engineering

In addition to its flexibility and transparency, environmentally friendly characteristics are added to the phototransistors that convert light into an electrical signal.

Korea University’s Professor Ju Byeong Kwon and doctoral researcher, Park Junsu together with Professor Seo Jung-Hun (University at Buffalo, The State University of New York) and the International Collaborative Research Team headed by Dr. Jhon Young Min (Korea Institute of Science and Technology) developed a biodegradable organic phototransistor based on cellulose.
* Organic phototransistor: Optical devices that convert light into electrical signals using organic semiconducting materials.

The importance of organic phototransistors is continuously emphasized because it can be widely applied to things such as the Internet of Things (IoT), but its use of toxic materials or opaque electrodes presents limitations in its application to to biomedical devices. In addition, as the problem of environmental pollution caused by e-waste has arisen, research into biodegradable electronics has become necessary.

The research team has developed an environmentally friendly non-toxic biodegradable optical device while maintaining the advantages of a flexible organic phototransistor.

The developed device is based on a cellulosic material, which is the main component of wood, and is degraded by wood decay fungus. Existing toxic substances have been replaced by non-toxic organic semiconductors

Also, using a transparent electrode presents excellent light transmittance. It was confirmed that photocurrents were generated when light of a specific color (red, green, blue) or white light was applied. The functional capabilities as a light sensor were proven as well.

Professor Ju Byeong Kwon, who was in charge of the research, said, "This research has developed an environmentally friendly optical sensor device that is flexible and transparent as well as biodegradable. In the future, it is expected that it can be used to develop a wearable product, especially a biomedical material, which requires high sensitivity of light detection in various types of curved surfaces.”

This research was supported by the Basic Research Project (Senior Researcher) of the Ministry of Science and Technology, Ministry of Information and Communication, Korea Research Foundation, and was published on May 7 as a cover paper in the international journal of nanoscience, Advanced Optical Materials.

* Paper title: Flexible and Transparent Organic Phototransistors on Biodegradable Cellulose Nanofibrillated Fiber Substrates
* Author Information: Professor Byeong-Kwon Ju (corresponding author, Korea University); Dr. Young Min Jhon (corresponding author,

Korea Institute of Science and Technology); Junsu Park (first author, Korea University); Professor Jung-Hun Seo (first author, University at Buffalo, The State University of New York); Dr. Seung-Won Yeom  (Korea University); Dr. Chunhua Yao (University of Wisconsin–Madison); Vina W. Yang (USDA Forest Service); Dr. Zhiyong Cai (USDA Forest Service)

(Figure1) Camera image and transmittance of a fabricated organic phototransistor
(a) Structure diagram of an organic phototransistor device (b-c) A photograph showing that the fabricated device is visually transparent and flexible to mechanical bending (d) Transmittance in the visible light region.
The organic phototransistor devices fabricated in this study are visually transparent and flexible for mechanical bending with a radius of 5 mm. Also, in the visible light region, the electrode material exhibits an excellent transmittance of 70.4%, about 28% higher than that of gold (Au)

(Figure 2) The degradation process of the device by brown rot fungus 
It can be confirmed that biodegradation is possible by exposing the fabricated organic phototransistor to wood decay fungus. The device exposed to the brown rot fungus is completely covered by the fungus after 9 weeks and exhibits a process of biodegradation with a weight reduction rate of 47.22% after 14 weeks.
 

(Figure 3) Cover page from the Book 6 Edition 9 of Advanced Optical Materials