Thermoelectric properties of organic semiconductors.
Lead Research Organisation:
University of Cambridge
Department Name: Physics
Abstract
The project is going to investigate the physics of the Seebeck coefficient, the electrical and thermal conductivity in high mobility conjugated polymers that are doped by solid-state diffusion. It is primarily an experimental project that aims to relate these transport coefficients to the electronic density of states and the structural dynamics, but the project will also involve elements of theoretical modeling.
People |
ORCID iD |
| Henning Sirringhaus (Primary Supervisor) | |
| Martin Statz (Student) |
Studentship Projects
| Project Reference | Relationship | Related To | Start | End | Student Name |
|---|---|---|---|---|---|
| EP/N509620/1 | 01/10/2016 | 30/09/2022 | |||
| 1805383 | Studentship | EP/N509620/1 | 01/10/2016 | 30/09/2019 | Martin Statz |
| Description | The performance of flexible electronic circuits and thermoelectric generators based on high-mobility conjugated polymers with field-effect mobilities comparable to or even exceeding those of amorphous silicon is not limited anymore by a broad distribution of the energetic sites in those material systems. Instead the energetic site distribution is narrow, with a standard deviation on the order of 26 meV, and transport as well as device performance can be improved by improving the interconnectivity of crystalline domains within a semicrystalline morphology or through extension of the size of the crystalline domains. It is a promising route to increase electron-electron interactions as well as modify electron-phonon interactions to boost device performance. (https://doi.org/10.1038/s42005-018-0016-5) Single-walled semiconducting carbon nanotube networks are another promising material system for both flexible electronics as well as flexible thermoelectric generators due to their high mobility and Seebeck coefficient as well as solution processability. A common approach to achieve highly selective semiconducting networks and even mono-chiral networks is via wrapping with polyfluorene polymers and subsequent centrifugation. Electrical transport is not affected strongly by these wrapping polymers due to the existence of sufficiently many tube-tube junctions. We developed measurement routines to perform gated respectively charge carrier density modulated thermoelectric transport measurements down to 50 K. Networks of different chirality distributions, network densities and length distributions have been investigated. We found that in the high density regime (> 13 um-1) neither electric nor thermoelectric transport is influenced by the network density. When oxygen and water trap states are removed from the networks via controlled dopant treatment, remarkably low enegetic disorder on the order of 12 meV is achieved in mono-chiral networks. We find that both electrical and thermoelectric transnport an be explained within the notions of transport in heterogenous media, fluctuation induced tunneling and Boltzmann transport formalism. Our findings provide design guidelines towards narrow energetic site distribution, large diameter SWCNT networks for both electronic and thermoelectric applications. The morphology, backbone-rigidity and monomer repeat unit length of high-mobility conjugated polymer semiconductors is expected to influence the total density of thermally accessible states as well as its distribution of the these energetic sites. Measurement techniques to investigate this relationship down to approx. 50 K have been established in this work. |
| Exploitation Route | The development of more accurate thermoelectric transport measurements will be used for thermoelectric transport studies of thin film semiconductors in which the charge density is either modulated electrostatically or chemically via doping with e.g. small molecules in our group and potentially other research groups. Insights into thermoelectric transport in high-mobility conjugated polymers and single-walled carbon nanotube networks facilitates material design guidelines such as extending the crystalline domains and improving their interconnectivity as well as chirality selection towards large diameter mono-chiral networks which will allow performance improvements of a variety of flexible electronics such as active-matrix displays as well as thermoelectric generators. |
| Sectors | Electronics,Energy,Healthcare |
| Description | Churchill College Conference Grant for Advanced Students and for Medical Electives |
| Amount | £350 (GBP) |
| Organisation | University of Cambridge |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 11/2019 |
| End | 03/2020 |
| Description | Churchill College travel grant for attending Gordon Research Conference |
| Amount | £235 (GBP) |
| Organisation | University of Cambridge |
| Sector | Academic/University |
| Country | United Kingdom |
| Start | 07/2018 |
| End | 07/2018 |
| Description | Australian Synchrotron |
| Organisation | Australian Synchrotron |
| Country | Australia |
| Sector | Public |
| PI Contribution | Thermoelectric transport measurements. |
| Collaborator Contribution | GIWAXS measurements on N2200. |
| Impact | DOI: 10.1038/s42005-018-0016-5 |
| Description | GIWAXS measurements |
| Organisation | Monash University |
| Department | Faculty of Engineering |
| Country | Australia |
| Sector | Academic/University |
| PI Contribution | Thermoelectric transport measurements. |
| Collaborator Contribution | GIWAXS measurements on N2200. |
| Impact | DOI: 10.1038/s42005-018-0016-5 |
| Description | Hitachi Laboratory Cambridge |
| Organisation | Hitachi |
| Country | Japan |
| Sector | Private |
| PI Contribution | Thermoelectric transport measurements. |
| Collaborator Contribution | Supervision |
| Impact | DOI: 10.1038/s42005-018-0016-5 |
| Description | SWCNT networks - University of Heidelberg |
| Organisation | Heidelberg University |
| Country | Germany |
| Sector | Academic/University |
| PI Contribution | Thermoelectric Transport in Single-Walled Carbon Nanotube Networks |
| Collaborator Contribution | Fabrication of devices |
| Impact | http://meetings.aps.org/Meeting/MAR20/Session/P53.6 |
| Start Year | 2017 |
| Description | Seebeck modelling University of New Mexico |
| Organisation | University of New Mexico |
| Department | Department of Physics and Astronomy |
| Country | United States |
| Sector | Academic/University |
| PI Contribution | Thermoelectric transport measurements. |
| Collaborator Contribution | Support with modelling transport data. |
| Impact | DOI: 10.1038/s42005-018-0016-5 |
| Start Year | 2012 |