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High-precision control of printed organic electrochemical transistors and displays

Linköping University have published results on printed organic electrochemical transistor circuits and displays in which the colour of individual pixels can be changed

7 Jul 2017 | Editor

Researchers at the Laboratory of Organic Electronics, Linköping University have recently published results on progress with printed organic electrochemical transistor circuits and displays in which the colour of individual pixels can be changed.

The organic electronics researchers used PEDOT:PSS - a conducting polymer - which conducts both electrons and ions. Displays and transistors manufactured from this polymer have many advantages, which include that they are simple and cheap to manufacture, and the material itself is non-hazardous.

However, it has been difficult to create devices that switch rapidly at a specific voltage, known as the "threshold voltage". This gives that it has, so far, been difficult to control the current state of the transistors or the colour state of the displays in a precise manner.

More than five years ago a wild idea arose at the Laboratory of Organic Electronics: could you solve this problem by combining electrochemistry with ferroelectricity? Ferroelectric materials consist of dipoles. One end of a dipole has a positive charge and the other a negative charge, and these "ferroelectric" dipoles rotate when they are exposed to an electric field beyond a specific threshold.

Head of the laboratory Professor Magnus Berggren couldn't let this idea rest, and when he was awarded a research grant from the Knut and Alice Wallenberg Foundation in December 2012 to use freely, this was one of the high-risk projects he chose to invest in.

After many years of tenacious experiments, Simone Fabiano and his colleagues at the Laboratory of Organic Electronics have managed to apply a thin layer of a ferroelectric material onto one electrode in organic electrochemical devices and circuits.

The Laboratory of Organic Electronics research group shows in the article that "ferroelectrochemistry", the combination of ferroelectricity and electrochemistry, can be used in displays in the field of printed electronics and in organic transistors. The scientists envisage, however, many other areas of application.

Linköping University - Ferroelektrokemi

Linköping University - Ferroelektrokemi

Figure: Linköping University - Ferroelektrokemi

The technology is now protected by patents.

Simone Fabiano, senior lecturer at the Laboratory of Organic Electronics, LOE, who is the principal author of the article in Science Advances, together with Negar Sani from the research institute RISE Acreo, said, "The lack of any threshold in the redox-switching characteristics of PEDOT:PSS hampers bistability and rectification, characteristics that would allow for passive matrix addressing in display or memory functionality."
Professor Magnus Berggren, Head of the laboratory, said, "We called the research then breakneck research, and here is a result. Our demonstration proves that truly leading research typically take a long time and require considerable patience. Simone Fabiano has done tremendous work here, and refused to give up when others have doubted."
Simone continued, "The thickness of the layer determines the voltage at which the circuit switches or the display changes colour. Transistors are no longer required in the displays: we can control them pixel-by-pixel simply through a thin ferroelectric layer on the electrode." Simone concluded, "Ferroelectrochemical components can easily be integrated into memory matrices and into bioelectronic applications, just to give a couple of examples."
magnus concluded, "The field of ferroelectrochemistry doesn't actually exist, but we have achieved success using this combination."

Ferroelectric polarization induces electronic nonlinearity in ion-doped conducting polymers

Simone Fabiano | Negar Sani | Jun Kawahara | Loïg Kergoat | Josefin Nissa | Zsak Engquist | Xavier Crispin | Magnus Berggren

Science Advances 30 Jun 2017 | Vol. 3, no. 6, e1700345 | DOI: 10.1126/sciadv.1700345


Poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) is an organic mixed ion-electron conducting polymer. The PEDOT phase transports holes and is redox-active, whereas the PSS phase transports ions. When PEDOT is redox-switched between its semiconducting and conducting state, the electronic and optical properties of its bulk are controlled. Therefore, it is appealing to use this transition in electrochemical devices and to integrate those into large-scale circuits, such as display or memory matrices. Addressability and memory functionality of individual devices, within these matrices, are typically achieved by nonlinear current-voltage characteristics and bistability—functions that can potentially be offered by the semiconductor-conductor transition of redox polymers. However, low conductivity of the semiconducting state and poor bistability, due to self-discharge, make fast operation and memory retention impossible. We report that a ferroelectric polymer layer, coated along the counter electrode, can control the redox state of PEDOT. The polarization switching characteristics of the ferroelectric polymer, which take place as the coercive field is overcome, introduce desired nonlinearity and bistability in devices that maintain PEDOT in its highly conducting and fast-operating regime. Memory functionality and addressability are demonstrated in ferro-electrochromic display pixels and ferro-electrochemical transistors.

www.liu.se/en/research/laboratory-of-organic-electronics    www.acreo.se    www.lintec-global.com   

About The Laboratory of Organic Electronics - Linkoping

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