The Exceptionally High Dielectric Constant of Doped Organic Semiconductors

The dielectric constant (ɛ_r) 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 ɛ_r 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 ɛ_r 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 ɛ_r and show the collective behavior of free charges in doped organic semiconductors.