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Electronic and optical properties of conducting polymers from quantum mechanical computations
KTH, School of Engineering Sciences (SCI), Applied Physics, Material Physics, MF.ORCID iD: 0000-0001-9970-5710
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

    Conductive polymers are also known as "organic metals" due to their semiconducting properties. They are found in a wide range of applications in the field of organic electronics. However, the growing number of experimental works is not widely supported with theoretical calculations. Hence, the field of conductive polymers is experiencing lack of understanding of mechanisms occurring in the polymers. In this PhD thesis, the aim is to increase understanding of conductive polymers by performing theoretical calculations.       

The polymers poly(3,4-ethylenedioxythiophene) (PEDOT) together with its selenium (PEDOS) and tellurium (PEDOTe) derivatives, poly(p-phenylene) (PPP) and naphthobischalcogenadiazoles (NXz) were studied. Several computational methods were applied for analysis of mentioned structures, including density functional theory (DFT), tight-binding modelling (TB), and Car-Parrinello molecular dynamics (CPMD) calculations. The combination of CPMD and DFT calculations was applied to investigate the PEDOT, PEDOS and PEDOTe. The polymers were studied using four different functionals in order to investigate the full picture of structural changes, electronic and optical properties. Temperature effects were studied using molecular dynamics simulations. Wide statistics for structural and molecular orbitals analysis were collected.        

The TB method was employed for PPP. The formation and motion of the excitations, polarons and bipolarons, along the polymer backbone was investigated in presence of electric and magnetic fields. The influence of non-magnetic and magnetic impurities was determined.       

The extended π-conjugated structures of NXz were computed using B3LYP and ωB97XD functionals in combination with the 6-31+G(d) basis set. Here, the structural changes caused by polaron formation were analyzed. The combined analysis of densities of states and absorption spectra was used for understanding of the charge transition.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. , p. 54
Series
TRITA-FYS, ISSN 0280-316X ; 2017:59
Keywords [en]
density functional theory, DFT, Car-Parrinello molecular dynamics, CPMD, tigh-binding, poly(3, 4-ethylenedioxythiophene), PEDOT, selenium, PEDOS, tellurium, PEDOTe, poly(p-phenylene), poly(para-phenylene), poly(1, 4-phenylene), naphthobischalcogenadiazoles
National Category
Condensed Matter Physics Polymer Chemistry
Research subject
Physics
Identifiers
URN: urn:nbn:se:kth:diva-214979ISBN: 978-91-7729-529-7 (print)OAI: oai:DiVA.org:kth-214979DiVA, id: diva2:1145019
Public defence
2017-10-27, Sal C, Kistagången 16, Kista, 10:00 (English)
Opponent
Supervisors
Note

QC 20170928

Available from: 2017-09-28 Created: 2017-09-27 Last updated: 2017-09-28Bibliographically approved
List of papers
1. Quantum Molecular Dynamical Calculations of PEDOT 12-Oligomer and its Selenium and Tellurium Derivatives
Open this publication in new window or tab >>Quantum Molecular Dynamical Calculations of PEDOT 12-Oligomer and its Selenium and Tellurium Derivatives
2017 (English)In: Journal of Electronic Materials, ISSN 0361-5235, E-ISSN 1543-186X, Vol. 46, no 5, p. 3071-3075Article in journal (Refereed) Published
Abstract [en]

We present simulation results, computed with the Car-Parrinello molecular dynamics method, at zero and ambient temperature (300 K) for poly(3,4-ethylenedioxythiophene) [PEDOT] and its selenium and tellurium derivatives PEDOS and PEDOTe, represented as 12-oligomer chains. In particular, we focus on structural parameters such as the dihedral rotation angle distribution, as well as how the charge distribution is affected by temperature. We find that for PEDOT, the dihedral angle distribution shows two distinct local maxima whereas for PEDOS and PEDOTe, the distributions only have one clear maximum. The twisting stiffness at ambient temperature appears to be larger the lighter the heteroatom (S, Se, Te) is, in contrast to the case at 0 K. As regards point charge distributions, they suggest that aromaticity increases with temperature, and also that aromaticity becomes more pronounced the lighter the heteroatom is, both at 0 K and ambient temperature. Our results agree well with previous results, where available. The bond lengths are consistent with substantial aromatic character both at 0 K and at ambient temperature. Our calculations also reproduce the expected trend of diminishing gap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital with increasing atomic number of the heteroatom.

Place, publisher, year, edition, pages
Springer, 2017
Keywords
PEDOT, PEDOS, PEDOTe, tellurium, density functional theory, dihedral angle
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-208238 (URN)10.1007/s11664-016-5161-6 (DOI)000398937900075 ()2-s2.0-85001037983 (Scopus ID)
Conference
35th International Conference on Thermoelectrics (ICT), 2016, Wuhan, PEOPLES R CHINA
Note

QC 20170627

Available from: 2017-06-27 Created: 2017-06-27 Last updated: 2017-09-28Bibliographically approved
2. Temperature dependence of band gaps and conformational disorder in PEDOT and its selenium and tellurium derivatives: density functional calculations
Open this publication in new window or tab >>Temperature dependence of band gaps and conformational disorder in PEDOT and its selenium and tellurium derivatives: density functional calculations
2017 (English)In: Journal of Chemical Physics, ISSN 0021-9606, E-ISSN 1089-7690Article in journal (Refereed) Published
Abstract [en]

The conducting polymer poly(3,4-ethylenedioxythiophene), or PEDOT, is an attractive material for flexibleelectronics. We present combined molecular dynamics and quantum chemical calculations, based on den-sity functional theory, of EDOT oligomers and isoelectronic selenium and tellurium derivatives (EDOS andEDOTe) to address the effect of temperature on the geometrical and electronic properties of these systems.With finite size scaling, we also extrapolate our results to the infinite polymers, i.e. PEDOT, PEDOS and PEDOTe. Our computations indicate that the most favourable oligomer conformations at finite temperature are conformations around the flat trans-conformation and a non-flat conformation around 45 from the cis-conformation. Also, the dihedral stiffness increases with the atomic number of the heteroatom. We find excellent agreement with experimentally measured gaps for PEDOT and PEDOS. For PEDOT, the gap does not increase with temperature where as this is the case for its derivatives. The conformational disorder as well as the choice of basis set both significantly affect the calculated gaps.

Place, publisher, year, edition, pages
American Institute of Physics (AIP), 2017
Keywords
PEDOT, selenium, tellurium, density functional theory, Car-Parrinello molecular dynamics
National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-214934 (URN)10.1063/1.4998509 (DOI)000412321600030 ()2-s2.0-85031789300 (Scopus ID)
Note

QC 20170928

Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-11-15Bibliographically approved
3. Polaron formation and optical absorption in PEDOT and its selenium and tellurium derivatives: density functional calculations
Open this publication in new window or tab >>Polaron formation and optical absorption in PEDOT and its selenium and tellurium derivatives: density functional calculations
(English)Manuscript (preprint) (Other academic)
Abstract [en]

We present a density functional theory (DFT) study on polaron formation and optical properties of PEDOT and its selenium and tellurium derivatives. Comparing a number of combinations of basis set and approximations to the exchange-correlation functional, we find that the ωB97XD functional is an overall good choice giving well-localized polarons and optical spectra in good agreement with experiment. This functional has the correct long-range  asymptotic behavior, and also includes some short-range Hartree-Fock exchange. Despite the  long-range Hartree-Fock exchange part present in this functional, the spin contamination remains relatively limited and it also stably produces results that are virtually independent of the basis set used.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-214935 (URN)
Note

QC 20170928

Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-10-30Bibliographically approved
4. Breakdown of Polarons in Conducting Polymers at Device Field Strengths
Open this publication in new window or tab >>Breakdown of Polarons in Conducting Polymers at Device Field Strengths
2017 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 121, no 19, p. 10317-10324Article in journal (Refereed) Published
Abstract [en]

Conducting polymers have become standard engineering materials used in many electronic devices. Despite this, there is a lack of understanding of the microscopic origin of the conducting properties, especially at realistic device field strengths. We present simulations of doped poly(p-phenylene) (PPP) using a Su-Schrieffer-Heeger (SSH) tight-binding model, with the electric field included in the Hamiltonian through a time-dependent vector potential via Peierls substitution of the phase factor. We find that polarons typically break down within less than a picosecond after the field has been switched on, already for electric fields as low as around 1.6 mV/angstrom. This is a field strength common in many flexible organic electronic devices. Our results challenge the relevance of the polaron as charge carrier in conducting polymers for a wide range of applications.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2017
National Category
Physical Chemistry
Identifiers
urn:nbn:se:kth:diva-209310 (URN)10.1021/acs.jpcc.7b02368 (DOI)000402024200008 ()2-s2.0-85020647285 (Scopus ID)
Funder
Swedish Research CouncilThe Royal Swedish Academy of SciencesKnut and Alice Wallenberg FoundationCarl Tryggers foundation Swedish Energy AgencySwedish Foundation for Strategic Research
Note

QC 20170619

Available from: 2017-06-19 Created: 2017-06-19 Last updated: 2017-09-28Bibliographically approved
5. Charge transport via polarons in doped poly(p-phenylene) with impurity
Open this publication in new window or tab >>Charge transport via polarons in doped poly(p-phenylene) with impurity
(English)Manuscript (preprint) (Other academic)
Abstract [en]

Polaron charge transport in doped poly(p-phenylene), PPP, in the presence of magnetic and nonmagnetic impurities and an electric field, is studied using the Su-Schrieffer-Heeger (SSH) tight-binding model. In our approach, the electric field is included in the Hamiltonian through the time-dependent vector potential via Peierls substitution of the phase factor. We describe the dynamics of the polarons and identify three distinct regimes: transmission, reflection, and trapping of polarons at the impurity site. The strength of the electric field as well as the impurity potential determine the outcome ofthe scattering.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-214937 (URN)
Note

QC 20170928

Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-10-30Bibliographically approved
6. Optical properties of Naphthobischalcogenadiazoles from density functional perspective
Open this publication in new window or tab >>Optical properties of Naphthobischalcogenadiazoles from density functional perspective
(English)Manuscript (preprint) (Other academic)
Abstract [en]

In the present work the density functional calculations of two naphthobischalcogenadiazole (NXz) oligomers are shown. The oxygen- and sulphur-containing NXz trimers were optimized in a form of a neutral oligomer and a radical cation in order to investigate structural changes resulting from the polaron formation. The influence of polaron on band gaps is determined and supported with densities of states analysis together with absorption spectra. This manuscript used B3LYP and ωB97XD functionals in combination with 6-31+G(d) basis set.

National Category
Chemical Sciences
Identifiers
urn:nbn:se:kth:diva-214936 (URN)
Note

QC 20170928

Available from: 2017-09-25 Created: 2017-09-25 Last updated: 2017-10-30Bibliographically approved

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