Charge Transport Properties of n-Type Conjugated Polymers and Photovoltaic Blends

Understanding of the charge transport properties of conjugated polymers is central to their applications in organic electronic devices, including organic light-emitting diodes, thin film transistors, electrochemical transistors, organic photovoltaics, thermoelectric devices, etc. Nevertheless, the underlying mechanisms of how molecular and supramolecular factors influence the charge transport properties of semiconducting polymers remain to be fully elucidated. In this talk, I will highlight some examples of our recent work in addressing this knowledge gap for n-type and p-type conjugated polymer films as well as for photovoltaic polymer blend films. Our studies in one area have investigated how polymer molecular weight influences the charge transport properties in two topologically distinct classes of n-type conjugated polymers – those with rigid-rod chain topology and those with semi-flexible chain topology – and found that the chain length dependence of carrier mobility and mechanism of electron transport depend on the polymer chain topology. A detailed characterization of the thin film microstructures of the materials provided insights on the structural disorder and energetic disorder as a function of polymer chain length. How side chain engineering and tuning of the donor-acceptor character on the ladder polymer backbone influence their thin film microstructures and charge transport properties are investigated in a series of p-type conjugated ladder polymers. In another example, we have investigated the charge transport properties of binary blends of interest in all-polymer solar cells, including the roles of the molecular weights of the polymer components in achieving bipolar-symmetric blend charge transport and optimal morphology, photophysics, and device efficiency.