469027 Linking Molecular Conformation to Charge Transport in Organic Materials
We use coarse-grained molecular dynamics simulations to simulate a variety of pristine morphologies of thiophene-based conjugated oligomers with different side-chain architectures and under various annealing protocols. The range of morphologies considered allows the analysis of several ordered and disordered structures, including hexagonally packed cylinders, ribbons and π-stacked lamellar structures, depending on the processing conditions. The charge transport characteristics are then determined for these morphologies using a combination of atomistic backmapping, efficient semi-empirical quantum chemical calculations that bypass the requirement for density functional theory, and kinetic Monte Carlo simulations to elucidate the hole mobility dependence on side-chain architecture and annealing temperature. Percolation analysis is also used to identify the structures that allow for the most efficient charge transport through the device. This demonstrates a highly-flexible, modular pipeline that can be used to connect sub nano-scale morphology to bulk thin-film behavior, informing future charge transport investigations and manufacturing processes alike.
Our data echoes experimentally obtained trends concerning the hole mobility, namely that increased annealing temperature and regioregular side-chain placement improves charge transport. Using our methodology, we quantify this behavior and attribute these trends to regular side-chain architectures permitting the assembly into closely-packed π-stacking crystals, amplifying the rate of inter-chain hopping, which is the limiting factor for efficient charge transport.