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Researchers in the US have used near-edge X-ray absorption fine-structure spectroscopy, or NEXAFS, to obtain detailed structural properties of organic semiconductors. Their findings could speed-up the development of reliable organic electronics devices, such as organic light-emitting diodes for flexible plastic displays, wearable electronics, radio frequency identity tags, and solar energy conversion systems.
Because NEXAFS is a non-destructive technique, it can provide detailed three-dimensional structural information about organic thin film semiconductors without the material being tested having to be sacrificed. The researchers used NEXAFS to track chemical changes, molecular reordering and defect formation in organic semiconductors over a range of processing temperatures from room temperatures to 300 Celsius. Their results could help industry reduce many of the high development costs that still represent an obstacle to the widespread commercial application of these materials.
Dean DeLongchamp and his colleagues at the National Institute of Standards and Technology (NIST) and the University of California Berkeley, evaluated how process-induced changes in thin-film composition and structure affected the movement of charge carriers (electron 'holes') in organic field effect transistors. They could monitor the conversion of the oligothiophene precursor to an organic semiconductor and found that a material with the highest levels of charge carrier movement was obtained at 250 Celsius and so exhibited maximum current flow.
The NEXAFS results also showed that optimum transistor performance was obtained when the individual molecules were aligned vertically relative to the flat device plane. NEXAFS has the potential to be the "ideal measurement platform for systematic investigation? of organic electronic materials", says DeLongchamp, "A straightforward means of correlating chemical and physical structure to the electronic performance of organic semiconductor films is a much-needed tool."
"The next step is to examine synthetic variation of the precursor and product to uncover the underlying motifs that result in better structure and, ultimately, better performance," DeLongchamp told spectroscopyNOW.
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DeLongchamp Team - DeLongchamp (top), Sharadha Sambasivan (bottom left), Daniel Fischer (bottom right). The equipment to the left is the NEXAFS spectroscopy beamline.
NEXAFS reveals chemical conversion, molecular re-ordering, and defect formation in oligothiophene precursor thin films (Credit: Wiley) |
