Higher-Performance Plastic Electronics

A new way of printing organic electronics is more reliable and yields higher performance.

It's possible to print large, flexible arrays of cheap, plastic transistors to drive displays. But the performance of these organic electronics is still not consistent enough for commercial devices. A new method for printing a wide variety of semiconducting organic compounds such as polymers is much more reliable--and on top of that, it improves the performance of a wide variety of these materials by a few orders of magnitude.

Smooth going: This thin film, made of a polymer consisting of silane and a hydrocarbon tail, is very smooth, which makes it a good substrate for growing high-performance organic electronics. Very few bumps can be seen in this atomic-force microscope image. Credit: Zhenan Bao

Organic electronics are cheaper than silicon-based electronics, but they tend to have lower performance. So they are being developed for applications where large area is important but performance doesn't need to be as high as it does inside a computer processor. What has kept these devices out of commercial products has been the difficulty of manufacturing them consistently.

In particular, the quality of the layered thin films used to make organic transistors often varies at the molecular level. The smoother and more regular the films are, the better they are at conducting electrons. So, Zhenan Bao, associate professor of chemistry at Stanford University, has developed a set of techniques for making consistently smooth, high-performance organic films.

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"This work is very important in terms of getting us to market with high-performance devices," says Vitaly Podzorov, professor of chemistry at Rutgers University.

Bao's group makes better organic transistors by focusing on the layer that lies directly underneath the electron-carrying semiconductor. In these devices, an electric current flows at the interface between the semiconductor and this underlying layer. Though the underlying layer is insulating, the properties of the interface between it and the semiconductor determine how fast electrons can move through the device. If it's rough, electrons can get trapped, cutting into device performance.