Polymer Photovoltaics
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Paresh Chokshi
Office: CPE 3.472 Phone: 512-471-4966 |
Kinetics of phase ordering in semi-flexible polymers under confinement
Polymeric films have been the focus of research due to their inherent presence in many emerging nano-technological devices like organic photovoltaic cells and OLEDs among others. In these applications, the device properties are governed by the prevailing morphology in polymer films. The comprehensive understanding of the process of domain formation, their growth and the resulting phase behavior can be helpful in designing materials with desired charge transfer characteristics.
The polymers of interest show nematic-like ordering upon quenching. By solving the time-dependent Ginzburg-Landau equation for the orientation as well as the component density order parameters, we examine the morphology development and study the kinetics of phase separation accompanied by thermally induced ordering. The mean-field free energy functional appropriate for melt, solution and blend is used. The anisotropy in diffusion coefficient creates ordered domains that are anisotropic shape. Further, the role of surface potential in morphology evolution is investigated for the case of confined geometries.
FIGURE: A snap-shot of concentration contours for semi-flexible polymer in solution depicting an anisotropic domain growth in a quenched system. The orientation of high-concentration domains gives the orientation of the director vector of nematic ordering.
Coarse-grained simulation to study the single-chain and multi-chain behavior of conjugated polymer in a poor solvent
Because of their semi-conducting behavior, the conjugated polymers (for example, derivates of poly-phenylene-vinylene, PPV) have been the main thrust of research activities in nano-science in last decade. The novel material based on conjugated polymers combines electronic properties of semi-conductors and processeability of plastics. Interestingly for these polymers, the electronic structure and hence the charge delocalization is very sensitive to the chain conformation and local packing of chains in spin-coated films. We carry out the coarse-grained Langevin dynamics simulation of single-chain conjugated polymer to examine the collapsed state of polymer chain in poor solvent. The role of single-bond defects (conjugation breaks) in chain folding will be investigated.