![]() ![]() So, the effect of g, in the interchain direction, on w is more relevant to our study. Second, we corroborate our model by fitting literature data of transport properties for a variety of conjugated polymers, and conclude that different classes of these possess distinct r values and effective DOS.Įlectronic density of states and paracrystallinityĬharge transport along polymer backbones (intrachain) is favorable due to stronger electronic coupling within the chain however, the electronic coupling between the backbones (interchain, π–π) is more critical since it dominates macroscopic transport properties in a real polymeric system 12, 13. First, we perform tight-binding (TB) model calculations supported by density functional theory (DFT) and molecular dynamics (MD), to confirm that the DOS tail exhibits a Gaussian shape whose width ( w) increases exponentially with g. ![]() We investigate the relationship between transport properties and the DOS determined by paracrystallinity in conducting polymers. We find that r affects the electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective DOS only affects the electrical conductivity. The scattering parameter ( r) is a physical factor that reflects a specific scattering mechanism. Several scattering mechanisms play a key role in shaping charge transport as defined by BTE formalism. In our work, we account for such structural disorder by using Gaussian DOS in the Boltzmann Transport Equation (BTE) under relaxation time approximation. Therefore, positional disorder plays the most important role in conjugated polymers with higher DOS widths ( w > 0.1 eV) 10. On the other hand, polaronic effect due to doping in organic semiconductors could alter the energetic disorder however, it can be negligible in intrinsically highly disordered polymers 10. For example, polarization effect, due to induced dipole moments, is a major cause of the energetic disorder in small molecules where positional disorder is almost neglected 11. However, their contributions to the total energetic disorder vary depending on the organic system under study. For instance, energy-dependent scattering was considered in describing charge transport in conducting polymers however, the DOS was not accounted for, resulting in partial understanding of charge transport 6.Įnergetic disorder in conducting polymers is caused by many factors such as positional disorder 1, dynamic effects 9, polarization, and polaronic effects 10, 11. Experimentally, thermoelectric studies provide a rigorous approach to probe energetics of charge scattering 6 with respect to structural morphology 7, 8. Although there have been some efforts to establish a charge transport model based on Gaussian DOS 5, energy-dependent scattering of the charge carriers was ignored, which is crucial in determining transport, especially in highly doped polymers that are useful for real-world applications. Those electronic states were shown to distribute in a Gaussian shape in energy space 3, 4, where its width ( w) is defined as energetic disorder. A general relationship between charge transport and paracrystallinity in conducting polymers is known 1, showing that higher g induces more states in a material’s electronic band gap, which limits charge transport in conducting polymers 2. The structural disorder is usually described by paracrystallinity ( g) which represents the fluctuation range of interchain spacings. ![]() These morphologies alter the degree of energetic disorder in the electronic structure significantly 1, 2. The diverse morphologies obtained from different processing methods obfuscate the fundamental understanding of charge transport in conducting polymers. We hope our results advance the fundamental understanding of charge transport in conducting polymers to further enhance their performance in electronic applications. Our model aligns well with the experimental transport properties of a variety of conducting polymers the scattering parameter affects electrical conductivity, carrier mobility, and Seebeck coefficient, while the effective density of states only affects the electrical conductivity. Furthermore, by using the Boltzmann Transport Equation, we find that transport can be understood by the scattering parameter and the effective density of states. We show that the tail of the density of states possesses a Gaussian form confirmed by two-dimensional tight-binding model supported by Density Functional Theory and Molecular Dynamics simulations. Here, we advance this understanding by presenting the relationship between transport, electronic density of states and scattering parameter in conducting polymers. The conceptual understanding of charge transport in conducting polymers is still ambiguous due to a wide range of paracrystallinity (disorder). ![]()
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