A research team led by Profs. Kim Jong-hyun and Kwon Oh-pil has successfully developed a high-performance gas sensor using an organic semiconductor. This will boost the electrical and optical gas detection capability of organic semiconductors and is expected to be utilized as a next-generation, high-sensitivity sensor to detect toxic gases.

Profs. Kim Jong-hyun and Kwon Oh-pil (Department of Applied Chemistry & Biological Engineering and Graduate School of Molecular Science and Technology) and a research team at the Ulsan National Institute of Science and Technology (UNIST) School of Energy and Chemical Engineering (ECHE) jointly announced development of the gas-detecting sensor.

Related research was published in the online edition of Advanced Functional Materials (IF: 18.808) an international journal in materials, under the title, “Strategic Approach for Enhancing Sensitivity of Ammonia Gas Detection: Molecular Design Rule and Morphology Optimization for Stable Radical Anion Formation of Rylene Diimide Semiconductors” on July 27, 2021.

Profs. Kim Jong-hyun (photo left) and Kwon Oh-pil (photo right) of Ajou University and Prof. Sang-kyu Kwak of UNIST took part in the research as corresponding authors, while Oh Byoung-min and Park Seong-ha, students at Ajou University Graduate School Department of Molecular Science & Technology, took part as first authors.

Ammonia (NH₃) gas, a volatile organic compound, is a highly toxic chemical. Inhalation of high concentrations for long periods of time can result in headache, nausea, coughing, difficulty breathing, and other reactions. A variety of studies have been carried out on the development of high precision detection technology due to the change in resistance of semiconductor materials. However, conventional inorganic semiconductors involve highly complicated manufacturing process, rendering elements of the sensors as very expensive. In contrast, organic semiconductor materials are limited in terms of detection function and detection selectivity.

The research team focused on ammonia gas and the organic semiconductor material based on rylene, which can selectively formulate stable radical anion. It discovered that when rylene-structured organic semiconductor material is exposed to ammonia gas, the intramolecular transfer charge reaction formulates stable radical anion and results in amplified electric current value and changes in light absorption. The research team utilized this to develop a high-performance gas sensor that can detect amounts of ammonia gas as tiny as 200ppb (parts per billion), while at the same time amplifying electric current to 1700% from ammonia gas.

The research team also verified the principle of efficient charge transfer reaction that occurs between ammonia gas molecules and rylene organic semiconductor molecules using quantum computation and also proposed the principles of sensor and material design. 

“The organic semiconductor material proposed in this study has a very simple combination process and even the tiniest amount of ammonia gas can create an amplified electric current signal through radical anion reaction,” said Prof. Kim. “This will allow us to overcome cost and detection limitations, which are issues in conventional gas sensors, and resolve the related problems.” He added, “The material we have developed will enable the development of high-sensitivity ammonia gas sensors that are also competitively priced.”

This research project was sponsored by the National Research Foundation (NRF) Research Facility Establishment Program (Molecular Science & Technology Research Center (MSTRC)), Basic Research in Science and Engineering (Mid-Career Researcher Program), and the International Cooperation and Leading Research Center Program (Functional Crystallization Center).

<Principle of stable radical anion formation using rylene organic semiconductors and performance of high-sensitivity ammonia gas sensor using this principle>

<July 27, 2021 online issue of Advanced Functional Materials >