Stabilization of Spontaneous Orientation Polarization by Preventing Charge Injection from Electrodes

The stability of the surface potential derived from spontaneous orientation polarization (SOP) in 2,2′,2″-(1,3,5-benzinetriyl)-tris(1-phenyl-1-H-benzimidazole) (TPBi) films was significantly improved by inserting an insulating layer at the electrode interface. The time of 20% potential loss from the initial value was extended from 1.3 days to 64 days in the dark at room temperature. Numerical simulations of the electrostatic potential in the films showed that the electrons accumulate at the surface region of the TPBi films in thermodynamic equilibrium, compensating for the internal electric field to decrease the surface potential. It was suggested that the insulating layer prevents electron injection from the electrode and stabilizes the surface potential.