Tying Together Multiscale Calculations for Charge Transport in P3HT: Structural Descriptors, Morphology, and Tie-Chains

Screening semiconducting polymers to discover design principles for tuning charge carrier mobility

We employ a rapid method for computing the electronic structure and orbital localization characteristics for a sample of 36 different polymer backbone structures. This relatively large sample derived from recent literature is used to identify the features of the monomer sequence that lead to greater charge delocalization and, potentially, greater charge mobility. Two characteristics contributing in equal measure to large localization length are the reduced variation of the coupling between adjacent monomers due to conformational fluctuations and the presence of just two monomers in the structural repeating units. For such polymers a greater mismatch between the HOMO orbitals of the fragments and, surprisingly, a smaller coupling between them is shown to favour greater delocalization of the orbitals. The underlying physical reasons for such observations are discussed and explicit and constructive design rules are proposed.

Why does solvent treatment increase conductivity of PEDOT:PSS? Insight from molecular dynamics simulations

Poly(3,4-ethylenedioxythiophene):polystyrenesulfonate (PEDOT:PSS) is one of the most important conducting polymers. In its pristine form its electrical conductivity is low, but it can be enhanced by several orders of magnitude by...

A tied Fermi liquid to Luttinger liquid model for nonlinear transport in conducting polymers

Organic conjugated polymers demonstrate great potential in transistors, solar cells and light-emitting diodes, whose performances are fundamentally governed by charge transport. However, the morphology-property relationships and the underpinning charge transport mechanisms remain unclear. Particularly, whether the nonlinear charge transport in conducting polymers is appropriately formulated within non-Fermi liquids is not clear. In this work, via varying crystalline degrees of samples, we carry out systematic investigations on the charge transport nonlinearity in conducting polymers. Possible charge carriers' dimensionality is discussed when varying the molecular chain's crystalline orders. A heterogeneous-resistive-network (HRN) model is proposed based on the tied-link between Fermi liquids (FL) and Luttinger liquids (LL), related to the high-ordered crystalline zones and weak-coupled amorphous regions, respectively. The HRN model is supported by precise electrical and microstructural characterizations, together with theoretic evaluations, which well describes the nonlinear transport behaviors and provides new insights into the microstructure-correlated charge transport in organic solids.

Low-Loss Organic Hyperbolic Materials in the Visible Spectral Range: A Joint Experimental and First-Principles Study

Hyperbolic media strengthen numerous attractive applications in optics such as super-resolution imaging, enhanced spontaneous emission, and nanoscale waveguiding. Natural hyperbolic materials exist at visible frequencies; however, implementations of these materials suffer substantial compromises resulting from the high loss in the currently available candidates. Here, the first experimental and theoretical investigation of regioregular poly(3-alkylthiophenes) (rr-P3ATs), a naturally low-loss organic hyperbolic material (OHM) in the visible frequency range, is shown. These hyperbolic properties arise from a highly ordered structure of layered electron-rich conjugated thiophene ring backbones separated by insulating alkyl side chains. The optical and electronic properties of the rr-P3AT can be tuned by controlling the degree of crystallinity and alkyl side chain length. First-principles calculations support the experimental observations, which result from the rr-P3AT's structural and optical anisotropy. Conveniently, rr-P3AT-based OHMs are facile to fabricate, flexible, and biocompatible, which may lead to tremendous new opportunities in a wide range of applications.

Thermal Transitions in P3HT:PC60BM Films Based on Electrical Resistance Measurements

In this paper, we present research on thermal transition temperature determination in poly (3-hexylthiophene-2,5-diyl) (P3HT), [6,6]-phenyl-C61-butyric acid methyl ester (PC60BM), and their blends, which are materials that are conventionally used in organic optoelectronics. Here, for the first time the results of electrical resistance measurements are explored to detect thermal transitions temperatures, such as glass transition Tg and cold crystallization Tcc of the film. To confirm these results, the variable-temperature spectroscopic ellipsometry studies of the same samples were performed. The thermal transitions temperatures obtained with electrical measurements are well suited to phase diagram, constructed on the basis of ellipsometry in our previous work. The data presented here prove that electrical resistance measurements alone are sufficient for qualitative thermal analysis, which lead to the identification of characteristic temperatures in P3HT:PC60BM films. Based on the carried studies, it can be expected that the determination of thermal transition temperatures by means of electrical resistance measurements will also apply to other semi-conducting polymer films.