2, Australian, Clayton, Victoria, Australia
3, Monash, Clayton, Victoria, Australia
4, Georgetown University, Washington, District of Columbia, United States
Recent demonstration of mobilities in excess of 10 cm2/Vs have energized research in solution deposition of polymers for thin film transistor applications. Due to the pi-stacking motif of most semiconducting polymers, the local mobility is expected to be intrinsically anisotropic. Fabrication of aligned films enables further optimization of device performance and can enable detailed structural characterization. Blade coating is an excellent prototyping tool for production deposition techniques such as slot die coating. Unlike slot die coating, a pre-metered technique, blade-coating is a self-metered technique and there exist two distinct operational regimes: the Landau-Levich or horizontal dip coating regime and the evaporative regime. We report results from blade coating a number of high performing polymer materials on unpatterned and nano-structured1 substrates. Depending on polymer and deposition regime, aligned films can be produced on unpatterned substrates. In general, the alignment appears nucleated at the air interface as bottom contact devices exhibit isotropic transport. In all cases, nano-structured substrates produce anisotropic bottom contact devices with the polymer chain aligned along the groove direction. The aligned films typically exhibit significant (c.a. 5 times) greater mobility than isotropic films. Detailed morphological studies suggest that the improvement in transport is related to alignment of the inter-crystallite regions (tie-chains). In-situ studies indicate that the coating induced alignment is facilitated by the presence of a lyotropic liquid crystal phase. The ability to independently control the alignment at the top and bottom of the films allows the deposition of novel, twisted structures.
1Tseng, H.-R., et al., Nano Letters 2012, 12, 6353-6357.