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Electrical Field Induced Alignment of P3HT Nanofibers
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Functional Materials, FNM. (Functional Materials Division)
KTH, School of Information and Communication Technology (ICT), Materials- and Nano Physics, Optics and Photonics, OFO.
Chemistry, Materials and Surfaces Unit, SP Technical Research Institute of Sweden.
Department of Sensor system, Acreo Swedish ICT AB.
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(English)Manuscript (preprint) (Other academic)
Abstract [en]

Abstract: Poly 3-hexylthiophene (P3HT) is one of the most studied conjugated polymers for organic solar cell applications due to its light weight, flexible processing methods and low cost fabrication. However, the hole mobility in P3HT is still relatively low compared to that of the inorganic semiconductors, which is one of the main challenges to achieve better performance of organic solar cells. The P3HT nanofibers with aligned by inducing an external electric field have been studied to improve the hole mobility in P3HT nanofibers. Here we present an AC electric field (1.3 V/µm, 50 Hz) induced alignment of P3HT nanofibers with two different lengths. The optical absorption spectra of aligned nanofibers were measured under different polarizations of incident light. The longer nanofibers showed higher dichroic raitos than that of shorter nanofibers, revealing a better alignment pattern. The photoconductivity of non-aligned and aligned P3HT nanofibers were measured and compared, where the aligned P3HT nanofibers showed a ~270% higher dark current than that of non-aligned sample. Moreover, the current measured under the illumination showed ~110% enhancement in the aligned P3HT nanofibers while only ~70% enhancement was obseved in non-aligned nanofibers, revealing that the alignment process have the potential to improve the mobility for optoelectronic applications. 

Keyword [en]
P3HT nanofibers, electric field induced alignment, J-V measurement
National Category
Nano Technology
URN: urn:nbn:se:kth:diva-187315OAI: diva2:929761

QC 20160520

Available from: 2016-05-19 Created: 2016-05-19 Last updated: 2016-05-20Bibliographically 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. 57 p.
National Category
Nano Technology
Research subject
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)

QC 20160519

Available from: 2016-05-19 Created: 2016-05-18 Last updated: 2016-05-20Bibliographically approved

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