The Exceptionally High Dielectric Constant of Doped Organic Semiconductors

Abstract

The dielectric constant (ɛr) is an essential parameter as it characterizes the ability to screen charge. Molecular doping is a key strategy to enhance the electronic properties of organic semiconductors, where again ɛr is important because the Coulomb attraction introduced by dopants needs to be overcome to generate carriers. Previous theoretical work has reported collective screening can lead to a dramatic enhancement of ɛr upon doping. Whereas this prediction has been tested in the low-doping regime, the predicted dielectric catastrophe remains unexplored. Here, metal-insulator-semiconductor (MIS) diodes to measure the dielectric constant of organic semiconductors subjected to moderate-to-high doping levels is employed. MIS diodes make it possible to measure the dielectric constant at relatively high doping ratios and corresponding high electrical conductivities. This results demonstrated a notable rise in the dielectric constant within a range of ≈3.0–15.0 of n- and p-doped organic semiconductors, resembling the phenomenon of dielectric catastrophe. These observations align with recent theoretical investigations into the impact of molecular doping on ɛr and show the collective behavior of free charges in doped organic semiconductors.