Engineers in the US have found a way to vastly speed up the performance of organic transistors, bringing closer the day when these thin, transparent semiconductors bring in a new generation of cheap, high-resolution TV screens, computer displays, and similar devices.
Writing in a recent online issue of Nature Communications, engineers from Stanford University and the University of Nebraska-Lincoln (UNL), describe how they made a semiconductor device with organic thin film transistors, or OTFTs that allowed electrical charge to travel much faster.
The ability to significantly improve speeds of travel of electrical charge – or carrier mobility – is something that has dogged scientists trying to get OTFTs to perform as well as silicon devices.
When that barrier is overcome, it paves the way for a new generation of cheap, fast, high-performance electronics capable of higher screen resolutions and rendering better motion and animation.
Such an achievement could bring down the cost, for example, of expensive, curved-screen television displays currently based on silicon technology.
Now in this new study, led by Zhenan Bao, professor of chemical engineering at Stanford, and Jinsong Huang, assistant professor of mechanical and materials engineering at UNL, they describe how they developed and tested a new way of making OTFTs with significantly faster carrier mobility.
Huang says this is the first time carrier mobility in OTFTs has reached levels comparable to that of silicon as seen in today’s high-end electronics.
He adds that their new method also resulted in high transparency of more than 90% over the visible spectrum, indicating its potential to produce transparent, high performance organic electronics.
New method uses ‘off-center spin coating’ to increase carrier mobility
To achieve this, the teams altered the basic process for making OTFTs, which usually involves dropping a special solution of carbon-rich molecules and plastic onto a spinning glass plate. The spinning action deposits a thin coat of the solution onto the plate.
The researchers made two changes to this process: first they spun the plate faster, and second, they coated only a small portion of it, about the size of a postage stamp.
These changes resulted in denser concentrations of organic molecules aligned more regularly, leading to improved carrier mobility.
The teams dubbed their innovative method “off-center spin coating,” and emphasize they are still very much at the experimental stage.
There are still some challenges, to overcome, such as how to precisely control the alignment of the organic materials in the transistor, or get carrier mobility to be uniform throughout.
The US Defense Advanced Research Projects Agency, Air Force Office of Scientific Research and the National Science Foundation helped fund the study.
