Bipolaron

About: Bipolaron is a research topic. Over the lifetime, 1335 publications have been published within this topic receiving 29154 citations. The topic is also known as: bipolarons.

Electronic Excitations and Metal-Insulator Transition in Poly(3-hexylthiophene) Organic Field-Effect Transistors

Abstract: We carry out a comprehensive theoretical and experimental study of charge injection in poly(3-hexylthiophene) (P3HT) to determine the most likely scenario for metal-insulator transition in this system. Wecalculate the optical-absorption frequencies corresponding to a polaron and a bipolaron lattice in P3HT. We also analyze the electronic excitations for three possible scenarios under which a first- or a second-order metal-insulator transition can occur in doped P3HT. These theoretical scenarios are compared with data from infrared absorption spectroscopy on P3HT thin-film field-effect transistors (FETs). Our measurements and theoretical predictions suggest that charge-induced localized states in P3HT FETs are bipolarons and that the highest doping level achieved in our experiments approaches that required for a first-order metal-insulator transition.

Comparison of Bipolaron-Like Charge State Generation in the Oxidative Doping of α,ω-Dithienyl and α,ω-Diphenyl Polyenes Stabilized by Methoxy and Methylthio Substituents.

Abstract: Several α,ω-dithienyl and diphenyl polyenes substituted with mesomerically interactive methylthio substituents have been synthesized by Wittig condensation. These polyenes can be oxidatively doped with SbCl5 in solution to yield stable bipolaron-like charge states. The methylthio-substituted bipolaron spectra are considerably more red-shifted in the diphenyl polyene series than the methoxy-substituted counterparts, or the methylthiothienyl series. The potential of these states for enhanced non-linear optical response is presented.

Effects of electron-electron interactions on the dynamic recombination of on-chain polaron pair and off-chain counterion in conjugated polymers

Abstract: Combining the one-dimensional Su-Schrieffer-Heeger model and the extended Hubbard model, we investigate the dynamic recombination of an on-chain same charged polaron pair with an off-chain counterion trapped in an impurity molecule We demonstrate that the bipolaron, the exciton and the trion are the main products in the polaron pair-counterion reaction and their yields depend sensitively on the electron-electron interactions In general, the on-site Coulomb interactions favor the creation of the exciton while the nearest-neighbor interactions favor the creation of the bipolaron However, the trion can also be formed directly with high yield via the polaron pair-counterion recombination by taking appropriate electron-electron interactions, which indicates that the trion formation model proposed by Kadashchuk et al is a feasible and effective channel Furthermore, we found that the yield of trion is proportional to the amount of charge trapped in the impurity injected into the main chain Our findings show that the electron-electron interactions play a key role in the dynamic recombination of elementary excitations in a conjugated polymer

Optical signature of bipolaron in monolayer transition metal dichalcogenides: all coupling approach

Abstract: We studied the optical signature of bipolaron and its effects on the bandgap modulation in the single-layer Transition Metal Dichalcogenides (TMDs) under magnetic field. Using the Huybrecht method, we derived the ground state energies in the modified zero Landau levels for all Frohlich coupling constants. We take into account both intrinsic longitudinal optical phonon modes and surface optical phonon modes induced by the polar substrate. We observed that the higher the coupling strength, the stronger is the magnetic field effect. The highest amplitude of the bandgap modulation is obtained for the MoS2 monolayer and the lowest with the WSe2 monolayer. We also found that the bipolaron is stable in TMDs. It is seen that the optical absorption presents the threshold values and respectively increases for WSe2, MoSe2, WS2 and MoS2.

On the validity of the bipolaron model for undoped and AlCl4- doped PEDOT

Abstract: The conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT) is one of the most highly researched materials, yet electronic structure investigations of conducting polymers are still uncommon. The bipolaron model has traditionally been the dominant attempt to explain the electronic structure of PEDOT. Though recent theoretical studies have begun to move away from this model, some aspects remain commonplace, such as the concepts of bipolarons or polaron pairs. In this work, we use density functional theory to investigate the electronic structure of undoped and AlCl4- doped PEDOT oligomers. By considering the influence of oligomer length, oxidation or doping level and spin state, we find no evidence for self-localisation of positive charges in PEDOT as predicted by the bipolaron model. Instead, we find that a single or twin peak structural distortion can occur at any oxidation or doping level. Rather than representing bipolarons or polaron pairs, these are electron distributions driven by a range of factors, which also disproves the concept of polaron pairs. Localisation of distortions does occur in the doped case, although distortions can span an arbitrary number of nearby anions. Furthermore, conductivity in conducting polymers has been experimentally observed to reduce at very high doping levels. We show that at high anion concentrations, the non-bonding orbitals of the anions cluster below the HOMO-LUMO gap and begin to mix into the HOMO of the overall system. We propose that this mixing of highly localised anionic orbitals into the HOMO reduces the conductivity of the polymer and contributes to the reduced conductivity previously observed.