Quantum chemical calculation studies on interface charge transfer between electrode and polyethylene under electrical stress

The mechanism of charge injection, the interface charge transfer between LDPE and SC (semi-conductive) or Al electrode, was investigated by using the density function theory (DFT) of Gaussian 09. The electric dipole layer between electrode (Al or SC) and LDPE is created after contact because Fermi levels between the LDPE and electrodes are difference. As the barrier height of hole injection (φ_Bh=1.29 eV) is low at the interface between SC electrode and LDPE, it can explain the experimental result of the positive charge injection from anode into the LDPE under the electric stress of 100 kV/mm. On the other hand, though the barrier height of electron injection (φ_Be=5.40 eV) is high at the interface between Al electrode and LDPE, the barrier height for electron was decreased by forming the reversal of electric double layers under higher electric stress. It can also explain the experimental result of the negative charge injection from Al cathode into the LDPE under above the electric stress of 150 kV/mm.