Determination of Hole Mobility in Crystalline Polyethylene by First-principles Calculation

Abstract

Degradation process of polymers is correlated with space charge, however there remains a lack of understanding of charge transport phenomena. Thus quantitative estimation of carrier mobility has not yet been accomplished. This is bacause, although charge transfer in solids are quantum mechanical, it has not been treated as such. In this research, hole mobility in crystalline polyethylene (PE) is computed by means of first principles calculation. It turns out that hole transfer in PE occurs in a hopping regime rather than a band regime even for crystalline structure without any structural disorders. In crystalline PE, hole hops between localized states that are created by polaronic effect. In addition, it was shown that hole mobilities in oligomers of PE are smaller by several orders of magnitude than those in naphthalene and anthracene, both due to small electronic coupling between molecules and large reorganization energy. Small electronic coupling and large reorganization energy is the result of σ bonded structure of the hole localized state of PE, which is different from π like structure of most organic semiconductor molecules.