Precise chemical doping of organic semiconductors in aqueous solution

A research team comprising NIMS, the University of Tokyo and the Tokyo University of Science has developed the world’s first technique capable of precisely doping an organic semiconductor into an aqueous solution without requiring a vacuum or d nitrogen atmosphere using special equipment.

This technique, which uses water, previously unexploited for this purpose, could bring progress, or even a paradigm shift. The study is published in the journal Nature.

Chemical doping is a crucial process in the production of semiconductor devices. Doping organic semiconductors involves the use of redox agents. Since effective redox agents tend to react with water and/or oxygen, they must be handled under vacuum or in a nitrogen atmosphere created using special equipment. Furthermore, these doping methods do not allow precise and consistent adjustment of doping levels.

These issues have long been major obstacles to technological progress in the organic semiconductor industry.

The research team recently developed a chemical doping technique that uses redox reactions between benzoquinone and hydroquinone in an aqueous solution under ambient conditions. The rate of these redox reactions can be controlled by the acidity of the solution (i.e., pH), a mechanism also present in electron transport chains during photosynthesis.

The team carried out chemical doping of thin films of organic semiconductors by immersing them in an aqueous solution containing benzoquinone, hydroquinone and hydrophobic ions.

Additionally, the team was able to precisely and consistently control doping levels by changing the pH of the solution, which made it possible to produce semiconductors with a wide range of electrical conductivity: approximately five orders of magnitude difference between minimum and maximum conductivity. .

Flexible and lightweight organic semiconductors can be used as suitable materials for inkjet printing and other low-cost printing processes. The chemical doping technique can be used to promote the industrial production of flexible organic film devices, including sensors, electronic circuits, displays, and solar cells.

Proof of concept of a thin-film pH sensor was also demonstrated through the use of this new technique, which suggests possibilities for applications in healthcare and biosensing.