Scientists solved mystery of low charge-carrier mobility in inkjet-printed films

1 Sep 2010.  NUS scientists at the Organic Nano Device Laboratory, in collaboration with researchers at A*STAR-funded Institute of Materials Research & Engineering (IMRE), have now solved the long-standing mystery of why inkjet-printed films of polymer semiconductors tended to show lower field-effect mobilities than spin-cast films.   Inkjet printing, widely seen now as a key green technology to fabricate large-area plastic electronic devices such as transistors and circuits on flexible foils, was originally developed for graphics printing.  In a recent paper published in Langmuir (L.Y. Wong et al. Langmuir 26 (2010) 15494), these scientists have reported a novel variable-angle spectroscopic ellipsometry methodology that has revealed that inkjet-printed plastic semiconductor films tend to be more crystalline and isotropic than spin-cast films. This leads to the formation of domain boundaries that impede the movement of the charge carriers in the film. By using an additional solvent annealing step to suppress the crystallisation, the scientists have further shown that it is possible to enhance the charge-carrier mobility of inkjet-printed films. “All you have to do after the printing is to briefly “cook” the printed circuits in a controlled solvent atmosphere to get back high charge-carrier mobilities,” says Loke-Yuen Wong, the lead author of the report, “This is a simple but effective step to develop high performance inkjet-printed electronic devices.” High charge-carrier mobilities will result in high performance and switching speeds.