Abnormal charge injection behavior at metal-organic interfaces

Abstract

Charge injection physics at metal-organic interfaces with barrier heights of 0.6--1.5 eV has been systematically studied. It is discovered that for sufficiently high barriers the injection current becomes temperature independent. The phenomenon contradicts the orthodox charge injection theory that predicts a simple exponential temperature dependence of charge injection. To explain the observed experimental results, tunneling injection via interfacial traps is proposed. The relative impact of various parameters such as trap density, energy level, and energy disorder is studied. The theoretical calculations indicate that interfacial deep traps, even of trivial amount, will have a huge impact on charge injection at various temperatures. Therefore trap states at the interface should be considered whenever barrier height is to be extracted from $I\text{\ensuremath{-}}V$ curves at various temperatures.