A simple droplet pinning method for polymer film deposition for measuring charge transport in a thin film transistor

Thin-film field-effect transistors (FETs) are widely used to evaluate charge transport properties of semiconducting polymers. Discovery of high performance materials require design and synthesis of new polymers. However, most polymers require multi-step synthesis and are difficult to be obtained in a large scale for comprehensive device evaluations. Here, we report a simple method to cast semiconducting polymer films from solutions with polymer concentration as low as 0.5 mg/mL, which is substantially less than typical values (similar to 10 mg/mL) used in conventional spin coating method. Here, we demonstrate that using this method, our cast films of a previously-reported polymer (PDPP-TT2T) exhibited field-effect mobility (mu(hole) = 0.89 +/- 0.13 cm(2) V s(-1), mu(e) = 0.025 +/- 0.005 cm(2) V-1 s(-1)), which is comparable to the reported values using the same device geometry. Furthermore, we extend this method to examine cast films of a pair of polymers (PDPP-3T-Ref. PDPP-3T-Si) to study the effect of siloxane substitution in the side chains on the molecular packing and their subsequent FEF performance. We observed that shorter pi-stacking distance (3.61 angstrom) for the siloxane-terminated polymer, when compared to that for the reference polymer (3.73 angstrom), resulted in improved FET performance (e.g., mu(hole) = 0.63 +/- 0.046 cm(2) V-1 s(-1) for PDPP-3T-Si vs mu(hole) = 0.17 +/- 0.062 cm(2) V-1 s(-1) for PDPP-3T-Ref). Taken together, this work presents an efficient alternative film-casting approach to produce polymer FETs that consumes much less material for their fabrication, lending viability for evaluation of various polymeric materials. (C) 2012 Elsevier B.V. All rights reserved.