Single-crystalline organic thin films: A predictive model that enables fast process optimization

Single crystalline organic thin film transistors (OTFTs) offer great potential for the realization of high-performance, low-cost flexible electronics. The most common methods to fabricate these layers directly on an inert substrate are all based on unidirectional solution coating techniques such as zone-casting, dip-coating or solution shearing. The quality of the resulting film strongly depends on the choice of solvent, coating speed and substrate temperature. So far, process optimization in literature has been conducted by trial and error methods, involving, for example, the variation of coating speeds over several orders of magnitude. Here, we show our recently developed model that enables the prediction of the coating speed for a given solvent-temperature combination. Thereby we are able to reduce the three dimensional parameter space by one dimension, enabling faster parameter screening and thereby process optimization. We show the validity of our approach by comparing it with results obtained by numerical simulations, experimental results published in literature and our own experimental results. We show the clear advantage of this approach in terms of processing steps needed to find a suitable process window. In the case of C8-BTBT, this leads to state of the art results with well-behaved OTFT characteristics with mobilities up to 7 cm2V/Vs and onset voltages close to zero volts.status: publishe