Direct determination of interfacial molecular orientations in field-effect devices of P3HT/PCBM composites by electron spin resonance
✍ Scribed by Shun-ichiro Watanabe; Hisaaki Tanaka; Hiroshi Ito; Shin-ichi Kuroda; Tatsuo Mori; Kazuhiro Marumoto; Yukihiro Shimoi
- Book ID
- 103877544
- Publisher
- Elsevier Science
- Year
- 2011
- Tongue
- English
- Weight
- 966 KB
- Volume
- 12
- Category
- Article
- ISSN
- 1566-1199
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✦ Synopsis
Field-induced electron spin resonance (FI-ESR) measurements have been performed on metal-insulator-semiconductor diode structures using regioregular poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C 61 -butyric acid methyl ester (PCBM) composites with various mixing ratios on a parylene gate insulator. For lower PCBM mixing ratios, clear FI-ESR signals of hole carriers were observed around g = 2.0031, with the external magnetic field normal to the substrate plane, indicating the edge-on orientation of P3HT lamellar structures at the device interface. On the other hand, for higher PCBM mixing ratios above 50 wt.%, a new additional peak was observed at g = 2.0022, which is characteristic of the pp-orbital axis, indicating the occurrence of flat-on P3HT domains. Ambipolar charge transport was also observed in field-effect transistors using P3HT/PCBM on parylene. With increasing PCBM fraction, from 0 to 100 wt.%, the field-effect mobility of holes decreased from 10 À3 to 10 À6 cm 2 /Vs, while that of electrons increased from 10 À5 to 10 À2 cm 2 /Vs. These results demonstrate that the flat-on orientation strongly reduces the charge carrier transport for holes because two-dimensional charge transport assisted by p-p interaction is interrupted by the presence of the flat-on structures.