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Electric field induced optical anisotropy of P3HT nanofibers in a liquid solution
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM.
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.ORCID iD: 0000-0002-0728-6684
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.ORCID iD: 0000-0002-3368-9786
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2015 (English)In: Optical Materials Express, ISSN 2159-3930, E-ISSN 2159-3930, Vol. 5, no 11, p. 2642-2647Article in journal (Refereed) Published
Resource type
Text
Abstract [en]

The nanofiber morphology of regioregular Poly-3- hexylthiophene (P3HT) is a 1D crystalline structure organized by π - π stacking of the backbone chains. In this study, we report the impact of electric field on the orientation and optical properties of P3HT nanofibers dispersed in liquid solution. We demonstrate that alternating electric field aligns nanofibers, whereas static electric field forces them to migrate towards the cathode. The alignment of nanofibers introduces anisotropic optical properties, which can be dynamically manipulated until the solvent has evaporated. Time resolved spectroscopic measurements revealed that the electro-optical response time decreases significantly with the magnitude of applied electric field. Thus, for electric field 1.3 V ·μm-1 the response time was measured as low as 20 ms, while for 0.65 V ·μm-1 it was 110-150 ms. Observed phenomenon is the first mention of P3HT supramolecules associated with electrooptical effect. Proposed method provides real time control over the orientation of nanofibers, which is a starting point for a novel practical implementation. With further development P3HT nanofibers can be used individually as an anisotropic solution or as an active component in a guest-host system.

Place, publisher, year, edition, pages
Optical Society of America, 2015. Vol. 5, no 11, p. 2642-2647
Keywords [en]
Anisotropy, Electric fields, Nanofibers, Real time control, Alternating electric field, Anisotropic optical properties, Crystalline structure, Electric field induced, Electrooptical response, Poly-3-hexylthiophene, Spectroscopic measurements, Static electric fields, Optical properties
National Category
Materials Engineering
Identifiers
URN: urn:nbn:se:kth:diva-181212DOI: 10.1364/OME.5.002642ISI: 000364467700027Scopus ID: 2-s2.0-84947753945OAI: oai:DiVA.org:kth-181212DiVA, id: diva2:902283
Note

QC 20160210

Available from: 2016-02-10 Created: 2016-01-29 Last updated: 2017-12-29Bibliographically approved
In thesis
1. Semiconducting Polymer Nanofibers and Quantum Dot based Nanocomposites for Optoelectronic Applications
Open this publication in new window or tab >>Semiconducting Polymer Nanofibers and Quantum Dot based Nanocomposites for Optoelectronic Applications
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Nanostructured materials have attracted a broad interest in various technologies such as optoelectronics. In this thesis, nanostructured semiconductor nanocrystals, including inorganic and organic materials, were fabricated by solution based methods. The reaction conditions were optimized to control the size and morphology of the obtained nanocrystals. The optical and photoelectric properties of nanocrystals were evaluated for potential optoelectronic applications.

Colloidal CdSe quantum dots (QDs) were synthesized via thermolysis method and layers of CdS was further grown on the core CdSe QDs to form a core-shell heterostructure quantum dots (HQDs). The optical properties of HQDs were evaluated and showed the characteristics of quasi-type-II alignment of energy levels, which has potential for excitonic solar cell (XSC) application.

Nanofibers of the semiconducting polymer poly-(3-hexylthiophene) (P3HT) were synthesized via a modified whisker method. In order to control the size (both the length and the diameter) of nanofibers, we systematically studied the ratio between mixture solvents and the solute concentration. In addition, the degradation processes of P3HT nanofibers on different substrates under various environments were investigated. We found that the degradation of P3HT nanofibers can be effectively suppressed by using the substrate of higher conductivity. A nanocomposite consisting of HQDs and P3HT nanofibers was fabricated and its photoelectric properties were evaluated by I-V measurements. A ‘turn-on’ voltage was found and revealed the localization of excited holes within the HQDs, which confirmed the quasi-type-II alignment between core and shell energy levels.

In addition, we aligned the P3HT nanofibers by applying the external electric field. Alternating current (AC) and direct current (DC) induced alignments of P3HT nanofibers were investigated respectively to study the effects of different electric fields on the alignment behavior. It was determined that the AC electric field allowed a better alignment of nanofibers. Moreover, two different lengths of P3HT nanofibers were aligned and their absorption spectra were measured. Under polarized light beams, we observed a better aligned pattern in the case of longer nanofibers, shown as a higher dichroic ratio calculated from optical absorption spectra. These aligned nanofibers may find applications in optoelectronic devices.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2016. p. 57
National Category
Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-187255 (URN)978-91-7595-946-7 (ISBN)
Public defence
2016-06-15, Sal C, Electrum, Isafjordsgatan 26, Stockholm, 10:00 (English)
Opponent
Supervisors
Note

QC 20160519

Available from: 2016-05-19 Created: 2016-05-18 Last updated: 2016-05-20Bibliographically approved
2. Electro-optical properties of one-dimensional organic crystals
Open this publication in new window or tab >>Electro-optical properties of one-dimensional organic crystals
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The recent development of photonics and applications puts new challenges for systems using emission, transmission and modulation of light. For these reasons, novel optical materials attract a special interest for their enabling properties for novel technologies.

In this work, we performed the research on fundamental properties and the possibility of implementation of electro-optical response of Poly-3-hexylthiophene-2,5-diyl (P3HT) nanofibers, which belong to the class of organic semiconductor crystalline materials. Our research demonstrated that an external electric field allows controlling the orientation of nanofibers dispersed in a solution by changing the electrical properties of P3HT crystals. This method was used to introduce a collective alignment of P3HT nanofibers and to impact the optical properties of the colloid. The spectroscopic and polarization measurements show that P3HT nanofibers possess optical anisotropy in a wide range of visible spectrum. This property combined with the ability to manipulate the orientation of nanofibers dynamically, was used for direct phase and intensity modulation of transmitted light. Along with these investigations, several engineering and technology tasks were solved. We have designed the transverse electro-optical cell using all-optical-fiber approach, as well as the longitudinal electro-optical cell was fabricated using a novel polymer molding technique.

The obtained research results demonstrate the potential of P3HT crystalline nanofibers as a material class of large niche of applications, not only limited to photovoltaics but also being implemented in electro-optical systems to control light polarization and propagation.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2017. p. 55
National Category
Nano Technology
Research subject
Physics
Identifiers
urn:nbn:se:kth:diva-220529 (URN)
Public defence
2017-11-24, Sal C, Electrum, Stockholm, 10:00 (English)
Supervisors
Note

QC 20171229

Available from: 2017-12-29 Created: 2017-12-22 Last updated: 2018-01-18Bibliographically approved

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