Issue 40, 2014

Revealing the origin of magnetoresistance in unipolar amorphous organic field-effect transistors

Abstract

We report on the magnetoresistance (MR) effect in a unipolar p-channel field-effect transistor based on amorphous thin film of low molecular weight 2,2′,7,7′-tetrakis(diphenylamino)-9,9′-spirobifluorene (Spiro-TAD). To scrutinize the origin of this effect two themes have been studied: (i) the influence of gate dielectric SiO2 surface treatment and (ii) the importance of organic molecular p-dopant 1,3,4,5,7,8-hexafluorotetracyanonaphthoquinodimethane (F6-TNAP) thin films sandwiched between SiO2 and Spiro-TAD. A device fabricated on bare SiO2 shows larger MR than one fabricated on hexamethyldisilazane-treated SiO2, suggesting the bipolaron species as the origin of this effect. This could be understood through two aspects. (i) The stabilization of bipolaron, i.e. trapped charge-stabilized bipolaron. Due to large energy cost for bipolaron formation, the stabilization of bipolaron by a trap with opposite sign is favored. Additionally, interface doping of Spiro-TAD with F6-TNAP reveals a significant enhancement in MR caused by an increase in trap density and charge carriers, boosting the effectiveness of bipolaron stabilization. (ii) Larger energetic disorder that might compensate the energy cost for bipolaron formation is expected to be obtained for a device fabricated on bare SiO2 caused by dipolar disorder at the corresponding interface. Adding a thin layer of F6-TNAP is expected to increase the energetic disorder as well.

Graphical abstract: Revealing the origin of magnetoresistance in unipolar amorphous organic field-effect transistors

Supplementary files

Article information

Article type
Paper
Submitted
07 apr 2014
Accepted
25 aug 2014
First published
27 aug 2014
This article is Open Access
Creative Commons BY license

J. Mater. Chem. C, 2014,2, 8569-8577

Revealing the origin of magnetoresistance in unipolar amorphous organic field-effect transistors

C. Isenberg and T. P. I. Saragi, J. Mater. Chem. C, 2014, 2, 8569 DOI: 10.1039/C4TC00702F

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