Additive Sweetens the Prospects for Organic Electronics [Chemical Engineering Progress]
(Chemical Engineering Progress Via Acquire Media NewsEdge) A sugary ingredient could put organic electronics on the map. Adding a small amount of this sweetener during the fabrication of organic semiconductors improves their yield and controls crystallization.
Researchers at the Univ. of California, Santa Barbara (UCSB) showed that a small amount of a nucleating agent offers more control over the formation of the semiconductor's microstructure, while increasing yield.
"We have developed a new method to utilize low-cost, environmentally friendly materials from the commodity chemical industry to control the performance of organic semiconductors," says Michael Chabinyc, an associate professor of materials at UCSB.
Organic semiconductors are the organic equivalents of materials such as silicon, which is used in today's mobile electronic devices. Unlike their inorganic counterparts, organic semiconductors could one day enable printable thin-film electronics.
Several challenges still exist, however, to the realization of organic electronics, such as their inferior performance, which is largely determined by the microstructure and crystallinity of the semiconductor material. While printing techniques provide for inexpensive manufacturing, control of the microstructure is not always maintained, leading to substantial variation in performance.
"The electrical properties of organic semiconductors depend critically on the way in which molecules pack together - the crystallinity," Chabinyc explains. "Gaining ways to control the crystallinity simply broadens the range of options for manufacturing," he says.
Chabinyc and his colleagues used two nucleating agents: l,3:2,4-bis(3,4dimethylbenzylidene)sorbitol (DMDBS), and tris-tert-butyl-1,3,5-benzenetrisamide (BTA). They added a small amount (0.1-1 wt.%) of each to several organic semiconductors, including poly(3-dodecylthiophene) (P3DDT), poly(3-hexylthiophene) (P3HT), the fullerene derivative [6,6]-phenyl-C61-butyric acid methyl ester (PCBM), and triisopropylsilylethynyl (TIPS) pentacene. The additives successfully controlled the semiconductors' solidification behavior without compromising their charge-transport properties.
Critical features of this strategy are that it is widely applicable to a broad range of organic semiconductors and that these capabilities are gained without negatively affecting the bulk electronic-transport properties of the final product, the researchers say.
With the nucleating agents, the researchers were able to inkjet-print a continuous film of the TIPS pentacene transistor, which is virtually impossible to do without the additive. The additive improved the yield from essentially zero to nearly 100%.
"Our work provides a pathway to aid in the further commercialization of these important materials," Chabinyc says.
M During solidification of a layer of PCBM (a type of fullerene with the structure shown here), the nucleating agents self-assemble in the PCBM films to form high-surface-area structures. Micrographs of the PCBM are shown here with (left) and without (right) the nucleating agent. Image courtesy of the Univ. of California, Santa Barbara
(c) 2013 American Institute of Chemical Engineers
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