Image-Force-Stabilized Interfacial Dipole Layer Impedes Charge Injection Into Disordered Organic Semiconductors

Feilong Liu, Yuhao Su, Xihong Lin, Li Nian, Bo Wu, Quan Niu, Harm van Eersel, Peter A. Bobbert, Reinder Coehoorn, and Guofu Zhou

Physics Review Applied (2022)

We show using three-dimensional kinetic Monte Carlo simulations that the injection of charge carriers from a metallic electrode into a disordered organic semiconductor is under nominally Ohmic injection conditions strongly impeded by the short-range Coulomb interactions between the charge carriers in the image-force-stabilized interfacial dipole layer. In contrast, master equation and conventional one-dimensional drift-diffusion simulations underestimate these Coulomb interactions due to their mean-field approximation, and are found not to reveal the effect. The simulations predict a reduction of the current density in organic semiconductor devices when the nominal injection barrier is taken very small or even negative, consistent with recent experimental results [Kotadiya et al., Nat. Mater. 17, 329 (2018)]. However, whereas in that work a modification of the energetic disorder near the interface is assumed, we find that the effect is already obtained after including charge-charge interactions beyond a one-dimensional and mean-field approximation.