First-Principle Investigation of Band Offset and Charge Transfer Characteristics at the PE/Fluorinated Layer Interface

Polymers, especially polyethylene (PE) are widely employed as insulating material in electrical power transmission system. However, the insulation still faces the problem of space charge which will distort the electric field distribution and accelerate electrical aging. Experimental results show that after the fluorination process, less charge injection occurs compared with pure PE. To clarify the mechanism, classical molecular dynamics was employed to build the PE/Fluorinated layer interfacial model and first principle calculation was utilized to get the band offset at the interface. The results calculated by both bulk plus band lineup method and layer-decomposed density of states method show that the energy band of the fluorinated PE layer is overall lower than that of the PE side, and the band offsets are around 2eV. Charge transport simulation based on Marcus theory and kinetic Monte Carlo also shows that charge can easily accumulate at the interfacial area under electric field and the band offset can suppress charge injection. The ΦCBO serves like an energy barrier for the excess electrons at the fluorinated layer side to cross the interface, while ΦVBO has the same effect on holes transport because of the energy barrier caused by inverted region. Our findings provide a fundamental and theoretical basis for material modification and space charge inhibition.