Localized state effects in polymer thin film transistors

Polymer semiconductors are of increasing interest for thin film transistors (TFT) and active matrix arrays, since their mobility is up to ∼0.1 cm2/V s, and they offer simple fabrication by solution-based printing. To understand the role of disorder and localized states in the polymers, we measure p-channel polythiophene and polyfluorene TFTs, using both spin-coated and jet-printed films, and infer localized states properties from the TFT characteristics. Bias stress effects occur in the polymer TFTs, which exhibit a threshold shift without significant change in mobility. Holes are removed from the channel at a rate proportional to the square of their concentration, suggesting the slow formation of hole bipolarons.