Influence of molecular dynamics on the dielectric properties of poly(9,9-di-n-octylfluorene-altbenzothiadiazole) -based devices

This paper uses Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) techniques to study the molecular relaxations and phase transitions in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), which has been extensively studied as the active thin film in organic devices....

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Bibliographic Details
Published in:IEEE transactions on dielectrics and electrical insulation 2012-08, Vol.19 (4), p.1181-1185
Main Authors: Faria, G. C., Seggern, H. V., Faria, R. M., deAzevedo, E. R.
Format: Article
Language:English
Subjects:
Correlation
Devices
Dielectric measurements
dielectric spectroscopy
Dielectrics
Differential scanning calorimetry
Diodes
F8BT
Glass
Glass transition
molecular relaxation
NMR
Nuclear magnetic resonance
organic electronics
Phase transformations
Phase transitions
Polymer
Polymers
Temperature measurement
Thin films
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Summary:This paper uses Nuclear Magnetic Resonance (NMR) and Differential Scanning Calorimetry (DSC) techniques to study the molecular relaxations and phase transitions in poly(9,9-di-n-octylfluorene-alt-benzothiadiazole) (F8BT), which has been extensively studied as the active thin film in organic devices. Besides the identification of the glass transition, β relaxation and crystal-to-crystal phase transition, we correlate such phenomena with dielectric and transport mechanisms in diodes with F8BT as the active layer. The β relaxation has been assigned to a transition at about 210 K measured by 1 H and 13 C solid state NMR, and can be attributed to local motions in the side chains. The glass transition has been detected by DSC and 1 H NMR. Dielectric spectroscopy (DS) carried out at low frequencies on diodes made from F8BT show two peaks which are coincident with the above transitions. This allowed us to correlate the electrical changes in the film with the onset of specific molecular motions. In addition, DS indicates a third peak related with a crystal-to-crystal phase transition. Finally, these transitions were correlated with changes in the carrier mobility recorded in thin films and published recently.
ISSN:1070-9878
1558-4135
DOI:10.1109/TDEI.2012.6259987