Delocalization Enhances Conductivity at High Doping Concentrations

Abstract

Many applications of organic semiconductors require high electrical conductivities and hence high doping levels. Therefore, it is indispensable for effective material design to have an accurate understanding of the underlying transport mechanisms in this regime. In this study, own and literature experimental data that reveal a power‐law relation between the conductivity and charge density of strongly p‐doped conjugated polymers are combined. This behavior cannot consistently be described with conventional models for charge transport in energetically disordered materials. Here, it is shown that the observations can be explained in terms of a variable range hopping model with an energy‐dependent localization length. A tight‐binding model is used to quantitatively estimate of the energy‐dependent localization length, which is used in an analytical variable range hopping model. In the limit of low charge densities, the model reproduces the well‐known Mott variable range hopping behavior, while for high charge densities, the experimentally observed superlinear increase in conductivity with charge density is reproduced. The latter behavior occurs when the Fermi level reaches partially delocalized states. This insight can be anticipated to lead to new strategies to increase the conductivity of organic semiconductors.

Charge polarity-dependent ion-insertion asymmetry during electrochemical doping of an ambipolar π-conjugated polymer

“…For example, the corresponding OECT I D,max in the case of ClO 4 − is 12 times higher than for NO 3 − change while the estimated densities of inserted ions are ~3 times higher. This is not surprising given the known super linear relation between doping density and conductivity in organic semiconductors 23 .…”

Organic Materials for Electronic and Thermoelectric Applications

“…This temperature and field dependence is studied by the time-of-flight technique and the transition temperature appears to be lower than in previous studies because of mobility overestimation in the former [43]. Note that mobility measurements can show different values depending on the used method [45] and of course molecular weight [3], [46]. The discrepancies were found between mobilities extracted from hole-only diodes and field effect transistors and believed to originate from the significant dependence of hole mobility on charge carrier density.…”

IonMonger 2.0: software for free, fast and versatile simulation of current, voltage and impedance response of planar perovskite solar cells

“…Weak molecular bonds in organic materials create a disordered structure in which electron transport takes the form of hopping between discrete molecular sites; this is in contrast to the band transport in ordered crystalline materials. For a system with a large number of molecules, this hopping transport resembles band transport in a Gaussian band [11,22,50,60] where the width of the Gaussian corresponds to the level of disorder in the intermolecular structure. The Gaussian band structure is shown in Fig.…”