Shrayesh Patel1
University of Chicago1
Our research delves into the intricate relationship between microstructure changes induced by thermal annealing and the resulting charge transport properties in poly(dodecyl-qaurterthiophene) (PQT). Employing targeted characterization techniques, including GIWAXS and ellipsometry, the study unveils the polymorphism and chain orientation within PQT and emphasizes the crucial role of interdigitation of side chains. Through vapor doping with F4TCNQ, the study demonstrates that polymorphs strongly control doping efficiency, thereby significantly influencing charge transport properties. Specifically, the research reveals that the 100 °C annealed sample, characterized by tightly packed side chains, displays low doping efficiency and corresponsing low electronic conductivity, whereas the 130 °C annealed sample exhibits markedly improved electronic conductivity from higher doping efficiency. Additionally, the study presents a novel method for fabricating continuously graded (CG) thin films of PQT using controlled thermal annealing, revealing diverse 1D in-plane microstructure gradient profiles modulating electronic conductivity and Seebeck coefficient across a 5 mm distance. Comparing these CG films to their equivalent uniform counterparts, the study showcases their enhanced cooling performance due to the effective redistribution of Joule heating and Peltier cooling effects. These findings underscore the significance of understanding the interplay between local order, polymorphism, and doping efficiency in molecularly doped conjugated polymers. In turn, this work provides valuable insights for the design of semiconducting polymers tailored for precise microstructure and doping levels for organic thermoelectric applications.