Spin casting is simple as high-tech manufacturing processes go, but finding the chemistry that allows spin casting to produce a high-performance ITO thin film has proven elusive. A key achievement described in the new paper, was finding the materials needed to make the nanoscale ITO crystals in the first place, said Shouheng Sun, professor of chemistry at Brown and the study's corresponding author.
The best chemicals turned out to be indium acetylacetonate and tin bis(acetylacetonate)dichloride. They synthesized ITO nanocrystals that had a narrow range of sizes, about 11 billionths of a meter in diameter. That consistency meant that when the crystals arranged themselves in the thin films, they neither bunched together in clumps, nor stayed too far apart. The result was a dense but evenly distributed array of crystals, which promotes conductivity.
"If the particle clumps, then you cannot get uniform assembly and you can't get good conductivity," Sun said.
This discovery was critical for achieving the high-level performance detailed in the paper, but the team knows it still needs to build on that progress for instance, to match the conductivity performance of films made by a process called sputtering.
"The next step is to improve conductivity to a magnitude commensurate with sputtered ITO while realizing the reduced cost and process efficiency benefits expected of a solution-based ITO deposition method," said Melissa Petruska, senior scientist at ATMI and co-author of the paper.
In new experiments, therefore, the team plans to further drive down electrical resistance, to reduce the length of time the films need to anneal, and to lay down fine patterns of their films, rather than continuous sheets, using inkjet or roll-to-roll printing.
|Contact: David Orenstein|