Effect of non-isothermal recrystallization on microstructure and transport in poly(thieno-thiophene) thin films

Abstract

We present the effect of recrystallization rate on the microstructure and charge transport properties of high-performance semiconducting polymer, poly(2,5-bis(3-alkylthiophen-2-yl)thieno[3,2-b]thiophene) (PBTTT), thin films. Differential scanning calorimetry (DSC) measurements indicate that the cooling rate directly influences the recrystallization process. In addition, atomic force microscopy (AFM) studies with an X-ray diffraction diagram demonstrate that slow cooling leads to well-connected large domains with enhanced three-dimensionally ordered structures, whereas fast cooling results in misaligned small domains with rough surfaces. At various temperatures, transport characteristics show an increase in the charge carrier mobility and a reduction in the activation energy with decreasing cooling rate of the films. Cooling rates slower than 15 degrees C/min induce the saturation of mobility and activation energy. These results assert that the cooling rate is a crucial factor for ordering in a microstructure as well as for the high performance of polymer thin films. (C) 2011 Elsevier B.V. All rights reserved.