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Molecular Origin of Charge Traps in Polyfluorene-Based Semiconductors

Faria, Gregório C. ; Azevedo, Eduardo R. de ; Seggern, Heinz von (2013):
Molecular Origin of Charge Traps in Polyfluorene-Based Semiconductors.
In: Macromolecules, 46 (19), pp. 7865-7873. American Chemical Society, ISSN 0024-9297,
[Article]

Abstract

The comprehensive control of morphology and structure is of extreme importance in semiconducting polymers when used as active layers in optoelectronic devices. In the work reported here, a systematic investigation of the structural and dynamical properties of poly(9,9-di-n-octyl-fluorene-alt-benzothiadiazole), known as F8BT, and their correlation with electrical properties is presented when the material is used as an active layer in optoelectronic devices. By means of X-ray diffraction, one observes that in thick layer films (thickness of about 4 pm) grown by drop-cast deposition, a solvent induced crystalline phase exists which evolves to a stable phase as the temperature is raised. This was not observed in thin films (thickness of about 250 nm) prepared by spin-coating within the investigated temperature range. By modeling the current-voltages characteristics of both thick and thin film devices, important information on the influence of crystallization on the trapping states could be drawn. Furthermore, the temperature dependence of the charge carrier mobility was found to be closely related to that of the molecular relaxation processes. The understanding of the nature of such molecular relaxations, measured by solid-state nuclear magnetic resonance methods, allows one to understand the importance of molecular relaxations and microstructure changes on the trap states of the system.

Item Type: Article
Erschienen: 2013
Creators: Faria, Gregório C. ; Azevedo, Eduardo R. de ; Seggern, Heinz von
Title: Molecular Origin of Charge Traps in Polyfluorene-Based Semiconductors
Language: English
Abstract:

The comprehensive control of morphology and structure is of extreme importance in semiconducting polymers when used as active layers in optoelectronic devices. In the work reported here, a systematic investigation of the structural and dynamical properties of poly(9,9-di-n-octyl-fluorene-alt-benzothiadiazole), known as F8BT, and their correlation with electrical properties is presented when the material is used as an active layer in optoelectronic devices. By means of X-ray diffraction, one observes that in thick layer films (thickness of about 4 pm) grown by drop-cast deposition, a solvent induced crystalline phase exists which evolves to a stable phase as the temperature is raised. This was not observed in thin films (thickness of about 250 nm) prepared by spin-coating within the investigated temperature range. By modeling the current-voltages characteristics of both thick and thin film devices, important information on the influence of crystallization on the trapping states could be drawn. Furthermore, the temperature dependence of the charge carrier mobility was found to be closely related to that of the molecular relaxation processes. The understanding of the nature of such molecular relaxations, measured by solid-state nuclear magnetic resonance methods, allows one to understand the importance of molecular relaxations and microstructure changes on the trap states of the system.

Journal or Publication Title: Macromolecules
Journal volume: 46
Number: 19
Publisher: American Chemical Society
Divisions: 11 Department of Materials and Earth Sciences
11 Department of Materials and Earth Sciences > Material Science
11 Department of Materials and Earth Sciences > Material Science > Electronic Materials
Date Deposited: 15 May 2017 09:31
Official URL: http://doi.org/10.1021/ma400648g
Identification Number: doi:10.1021/ma400648g
Funders: G.C.F. acknowledges a fellowship awarded by the "Fundacao de Amparo a Pesquisa do Estado de Sao Paulo" (FAPESP) (Proc. number 2008/01935-5 and 2012/01303-4) ., G.C.F. acknowledges the funding by the "Deutscher Akademischer Austauschdienst" (DAAD) (A/09/72945; ref 415)., The authors are also grateful to the Brazilian funding agencies FAPESP (Proc. number 2009/18354-8 and 2007/08688-0), CNPq and MCT/INEO for funding., H.v.S. acknowledges the scholarship "Special Visiting Researcher" by the Brazilian Science without Borders Program (CNPq and Capes, Proc. number 400133/2012-1).
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