From Event: SPIE Organic Photonics + Electronics, 2015
Semiconducting polymers play an important role in a wide range of optical and electronic material applications. Polymer thin films that result in the highest performance typically have a complex semicrystalline morphology, indicating that considerable device improvement can be achieved through optimization of microstructural properties. However, the connection between molecular ordering and device performance is difficult to predict due to the current need for a mathematical theory of the physics that dictates charge transport in semiconducting polymers. It is experimentally suggested that efficient transport in such films occurs via connected networks of crystallites. We present an analytical and computational description of semicrystalline conjugated polymer materials that captures the impact of polymer conformation on charge transport in heterogeneous thin films. We first develop an analytical theory for the statistical behavior of a polymer emanating from a crystallite and predict the average distance to the first kink in the chain that traps a charge. We use this analysis to define the conditions for percolation and the consequent efficient transport through a semicrystalline material. We then establish a charge transport model using Monte Carlo simulations that predicts the multi-scale charge transport and crystallite connections. We approximate the thin film as a two-dimensional grid of crystallites embedded in amorphous polymer. The chain conformations in the amorphous region are determined by the wormlike chain model, and the crystallites are assigned fixed mobilities. We use this model to identify limits of charge transport at various time scales for varying fraction of crystallinity.
Sonya A. Mollinger, Brad Krajina, Rodrigo J. Noriega-Manez, Alberto Salleo, and Andrew J. Spakowitz, "Percolation, tie-molecules, and microstructural origins of charge transport in semicrystalline conjugated polymers (Presentation Recording)," Proc. SPIE 9568, Organic Field-Effect Transistors XIV; and Organic Sensors and Bioelectronics VIII, 95680V (Presented at SPIE Organic Photonics + Electronics: August 12, 2015; Published: 5 October 2015); https://doi.org/10.1117/12.2188455.4519372063001.
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