August 9, 2007 – Researchers at the U. of Texas/Austin say they’ve developed a nanoparticle technique that provides more insight into the formation of “deep traps,” which are desired for memory devices built with plastic semiconductors but undesirable for things like solar cells and LEDs.
Deep traps — explained by the researchers as electrical charges essentially falling into holes when traveling through a semiconductor — are desirable for memory devices, but can decrease efficiency of the material’s electrical conductivity, precisely the wrong property to have in, say, a solar cell. Previous techniques to study deep traps typically involved completed and complex semiconductor devices, noted Rodrigo Palacios post-doctoral fellow at UT/Austin’s Center for Nano and Molecular Science and Technology, in a statement.
To better understand this phenomenon, a team of researchers developed a single-particle technique to study small portions of semiconductor material at the nanoscale. Their research, appearing in an advanced online publication of the journal Nature Materials, used single-molecule spectroelectrochemistry to study oxidation of nanoparticles of a conjugated polymer named “F8BT” (poly(9,9-dioctylfluorene-co-benzothiadiazole)).
Shining light on F8BT particles and measuring the changes in resulting fluorescence intensity showed deep traps forming as the semiconductor nanoparticles were charged and uncharged. “A reversible hole-injection charging process has been observed that occurs primarily by initial injection of shallow (untrapped) holes, but soon after the injection, a small fraction of the holes becomes deeply trapped,” according to the published paper.
“With our new technique, we got detailed information on how these deep traps are formed and how long they live,” information that can help improve devices made from conjugated polymers, and design new materials that can either avoid deep traps or form them better, Palacios noted.
IMAGE: Microscopic image of nanoparticles of the plastic semiconductor material F8BT. (Source: U. of Texas/Austin)