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Sunday, 23 Sep 2018

Researchers develop the world's first complementary electrochemical logic circuits

Applications of the organic components include logic circuits that can be printed on textile or paper, various types of cheap sensor, non-rigid and flexible displays, and – not least – the huge field of bioelectronics

LOE - Complementary logic circuit : Photo credit: Thor Balkhed

15 Jan 2018 | Editor

Researchers at the Laboratory of Organic Electronics have developed the world's first complementary electrochemical logic circuits that can function stably for long periods in water. The researchers believe this to be highly significant breakthrough in the development of bioelectronics.

The first printable organic electrochemical transistors were presented by researchers at LiU as early as 2002, and research since then has progressed rapidly. Several organic electronic components, such as light-emitting diodes and electrochromic displays, are already commercially available.

The dominating material used until now has been PEDOT:PSS, which is a p-type material, in which the charge carriers are holes. In order to construct effective electron components, a complementary material, n-type, is required, in which the charge carriers are electrons.

It has been difficult to find a sufficiently stable polymer material, one that can operate in water media and in which the long polymer chains can sustain high current when the material is doped.

In an recent research article in Advanced Materials, Simone Fabiano, head of research in the Organic Nanoelectronics group at the Laboratory of Organic Electronics, presents, together with his colleagues, results from an n-type conducting material in which the ladder-type structure of the polymer backbone favours ambient stability and high current when doped.

One example is BBL, poly(benzimidazobenzophenanthroline), a material often used in solar cell research. Postdoctoral researcher Hengda Sun has found a method to create thick films of the material. The thicker the film, the greater the conductivity. The method can also be successfully used together with printed electronics across large surfaces. Hengda Sun has also shown that the circuits function for long periods, both in the presence of oxygen and water.

Applications of the organic components include logic circuits that can be printed on textile or paper, various types of cheap sensor, non-rigid and flexible displays, and – not least – the huge field of bioelectronics. Polymers that conduct both ions and electrons are the bridge needed between the ion-conducting systems in the body and the electronic components of, for example, sensors.

"We have used spray-coating to produce films up to 200 nm thick. These can reach extremely high conductivities."


"This may appear at first glance to be a small advance in a specialised field, but what is great about it is that it has major consequences for many applications. We can now construct complementary logic circuits – inverters, sensors and other components – that function in moist surroundings."


Simone Fabiano, Head of Research in the Organic Nanoelectronics group at the Laboratory of Organic Electronics

"Resistors are needed in logical circuits that are based solely on p-type electrochemical transistors. These are rather bulky, and this limits the applications that can be achieved. With an n-type material in our toolbox, we can produce complementary circuits that occupy the available space much more efficiently, since resistors are no longer required in the logical circuits."


Magnus Berggren, Professor of organic electronics and head of the Laboratory for Organic Electronics

Complementary Logic Circuits Based on High-Performance n-Type Organic Electrochemical Transistors

Hengda Sun | Mikhail Vagin | Suhao Wang | Xavier Crispin | Robert Forchheimer | Magnus Berggren | Simone Fabiano

open access | First published: 10 January 2018 | DOI: 10.1002/adma.201704916

Abstract

Organic electrochemical transistors (OECTs) have been the subject of intense research in recent years. To date, however, most of the reported OECTs rely entirely on p-type (hole transport) operation, while electron transporting (n-type) OECTs are rare. The combination of efficient and stable p-type and n-type OECTs would allow for the development of complementary circuits, dramatically advancing the sophistication of OECT-based technologies. Poor stability in air and aqueous electrolyte media, low electron mobility, and/or a lack of electrochemical reversibility, of available high-electron affinity conjugated polymers, has made the development of n-type OECTs troublesome. Here, it is shown that ladder-type polymers such as poly(benzimidazobenzophenanthroline) (BBL) can successfully work as stable and efficient n-channel material for OECTs. These devices can be easily fabricated by means of facile spray-coating techniques. BBL-based OECTs show high transconductance (up to 9.7 mS) and excellent stability in ambient and aqueous media. It is demonstrated that BBL-based n-type OECTs can be successfully integrated with p-type OECTs to form electrochemical complementary inverters. The latter show high gains and large worst-case noise margin at a supply voltage below 0.6 V.

www.liu.se/en/research/laboratory-of-organic-electronics   


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