Molecular Origin of Charge Traps in Polyfluorene-Based Semiconductors

Author(s)

Faria, Gregorio C. ^{[1, 2]} ; deAzevedo, Eduardo R. ^[1] ; von Seggern, Heinz ^[2]

Affiliation

^[1] Univ Sao Paulo, Inst Fis Sao Carlos, BR-13560970 Sao Carlos, SP - Brazil

^[2] Tech Univ Darmstadt, Inst Mat Sci, D-64287 Darmstadt - Germany

• Document type: Journal article
• Source: MACROMOLECULES; v. 46, n. 19, p. 7865-7873, OCT 8 2013.
• Web of Science Citations: 10

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. (AU)

• FAPESP's process: 07/08688-0 - Electronic and optoelectronic polymer devices
• Grantee: Roberto Mendonça Faria
• Support Opportunities: Research Projects - Thematic Grants
• FAPESP's process: 09/18354-8 - Dynamics and structure of polymer systems as studied by nuclear magnetic resonance
• Grantee: Eduardo Ribeiro de Azevedo
• Support Opportunities: Regular Research Grants
• FAPESP's process: 08/01935-5 - Correlation between electric and optical properties with molecular dynamics and physical structure of films and organic devices of polyfluorenes and its derivatives
• Grantee: Gregório Couto Faria
• Support Opportunities: Scholarships in Brazil - Doctorate
• FAPESP's process: 12/01303-4 - Structural and morphological characterization of conjugated polymer films for application on high performance photo-voltaic devices
• Grantee: Gregório Couto Faria
• Support Opportunities: Scholarships in Brazil - Post-Doctoral