Bias dependent dipolar electric field at self-assembled monolayer (SAM)/organic interface determines the hole drift mobility

Abstract

The room-temperature current-voltage data of hole transport in ITO/PFB(400 nm)/Al organic diode (Khodabakhsh et al., 2004) where PFB is polyfluorene copolymer, and the related 5 devices of different self-assembled monolayer (SAM) with permanent molecular dipole moments chemisorbed onto the indium-tin-oxide (ITO) electrode are investigated. It is shown that the intrinsic hole mobility, μmax, within the diode is Ea independent but it is strongly dependent on the magnitude and the orientation of the SAM´s permanent molecular dipole moments. The current-density data jointly with the reported values of 4 SAM’s molecular dipole moments and their orientation with respect to the ITO normal at the contact enable to provide an estimate of the PEDOT:PSS, as well as pristine ITOP/PFB molecular dipole moments and their orientations. The dipolar electric field that is induced at the ITO/SAM/PFB interface, Eint, turns out to be a linear function of the applied field Ea of approximately SAM`s independent slope. The current-density induced dipolar electric field occurs even at the pristine ITO/PFB interface. The intrinsic hole mobility, μmax, multiplied by the given algebraic function of the Ea dependent interfacial electric field, Eint, combine into the Ea dependent hole drift mobility, μd, Influenced jointly by the dipolar and interfacial effects, it is the parameter that is amenable in the current-density-voltage measurements. The relevance of the stated findings to the current switching mechanism in the self-assembled supramolecular ferroelectric organic semiconductor diode is also briefly discussed.