The discovery that organic materials can conduct electricity was made in the early 1970s. These achievements eventually led to a Nobel Prize in Chemistry in 2000 for the three scientists behind the discovery. Organic electronics have now found their way into everyday life, replacing traditional technology in smart phone displays and offering new solutions for solar cells and LEDs.

Gao has spent his career developing ways to further expand the use of organic electronics.

“To develop electronic devices using organic materials, we need to find ways to give these carbon-based materials similar properties as traditional inorganic semiconductors,” says Gao, who is a professor of optoelectronics.

Doping organic materials

Organic materials don’t naturally conduct electricity well. To make them useful for electronic devices, they must be able to carry electrical current.

Doping entails adding other substances to a material to create an excess or deficit of electrons — dramatically boosting their ability to conduct electricity. This technique has been widely used in traditional inorganic semiconductors; for example, silicon, the backbone of modern electronics, is doped with phosphorus or arsenic to improve its conductivity.

There are two types of doping. Creating a deficit of electrons is known as p-doping, which has long been successfully used for organic materials. Creating an excess of electrons is called n-doping; adding electrons to hydrocarbon-based organic material has proven much more difficult.

“N-doping has been particularly challenging for organic semiconductors. The substances used for n-doping are easily affected by oxygen in the air resulting in highly unstable materials.”

To match the performance of traditional semiconductors, it is necessary to achieve both p-doping and n-doping of organic materials. There has been intense international research in this field over the past few decades, and Gao has now identified a potential way forward.

“Our idea involves introducing a third material during the doping process. This may provide more stability and better control over the process. It may also protect the doping agent from oxidization.”

From energy applications to neuromorphic technology

Addition of a third substance can be likened to using a catalyst and has already been successfully done by Gao’s research team in p-doping. In that case, an organic salt was used. Initial n-doping experiments will follow this route but with a more delicate molecule design. It is hoped this will result in more successful n-doping.

Organic materials are light-weighted, flexible, and can be printed like paper ink. With effective doping, such materials can be used in a new generation of solar cells and LEDs, supporting green and sustainable industry development.

For me, research is about finding answers to questions that people do not yet fully understand and contributing to new solutions. That drives much of my work.

“If we succeed, the first applications for the material could be new types of energy-conversion devices, such as solar cells and LEDs. We also hope to use the material to create neuromorphic circuits.”

Neuromorphic circuits are electronic circuits inspired by the brain’s way of processing information, and they can be used to build faster and more energy-efficient systems. Organic materials can enable brain-like neuromorphic computing with outstanding energy efficiency and speed. Their biological similarity also makes them well suited for medical devices such as brain implants and biosensors.

“For neuromorphic applications, we will work with our collaborators in Norrköping who have made important advances in this area. But first we need to demonstrate that our method for n-doping organic materials works,” he says.

From Cambridge to Linköping

Gao earned his PhD at Cambridge in England, where he came into contact with Olle Inganäs, now a professor emeritus at Linköping University. Inganäs made early breakthroughs in organic solar cells.

“After completing my dissertation, I contacted Olle for a postdoctoral position. At the time, he had received the Wallenberg Scholar grant and could offer me a position in Linköping.”

Initially reluctant to move to a cold country like Sweden, Gao planned to stay only for two years. Over a decade later, he has settled here with his family. He became a professor in 2020 and has led several international projects, including developing new materials for solar cells.

Life as a researcher was not a childhood dream. But his thirst for knowledge gradually grew during his studies.

“One of the best things about academia is that you are constantly encouraged to push boundaries, explore new areas, and solve more challenges – even in fields that may be completely new to you,” says Gao.

Text Magnus Trogen Pahlén
Translation Maxwell Arding
Photo Magnus Bergström