From Polyethylene to Polystyrene: First Principles Prediction of carrier mobility

Recently, we have successfully evaluated the carrier transfer properties in polyethylene (PE) with the aid of a first-principles based multi-scale modeling method. In order to develop a framework for materials design, it is crucial to assess the robustness and versatility of our model. Thus, in this study, carrier transfer properties in benzene doped PE oligomer, which gives implications of that in polystyrene (PS) is investigated. Both the partial density of states of benzene/PE oligomer cluster and the ionization energies of benzene molecules and PE oligomers show that hole localized states at benzene molecules are energetically favorable compared to those at PE oligomers. Indeed computed hole hopping rates from PE oligomers to benzene molecules are larger than those from benzene molecules to PE oligomers. However, since (1) the reorganization energy of hole transfer between PE oligomers (similar to 900 meV) are larger than those between PE oligomers and benzene molecules (similar to 600 meV), and (2) the electronic couplings between PE oligomers are (similar to 10 meV) smaller than that between PE oligomers and benzene molecules (several tens of meV), hole hopping rates from benzene molecules to PE oligomers are larger than those between PE oligomers. Accordingly, the hole mobility in benzene doped PE oligomer increases with increasing benzene concentration. This is in line with experimental findings that the hole mobility in PS is larger than that in PE. These findings emphasize the necessity of evaluating the microscopic parameters that are relevant to carrier transfer.