The dielectric relaxation of semiconducting RR P3HT
Organic semi-conducting polymers have been the focus of many studies because of their potential applications in filed effect transistors and light emitting diodes. One of the materials typically used as an organic semiconductor is a regioregular poly(3-hexylthiophene) (P3HT). It was shown, that the packing structure, the molecular orientation and the molecular weight affect electronic properties and filed effect mobility. Although, the electrical mobility properties of P3HT have been widely investigated, the dielectric relaxation processes have not been systematically investigated.
Dielectric spectra of organic polymers typically reveal several relaxation processes that are related to structural and local molecular dynamics. We investigated the dielectric response of P3HT films in the temperature range of 240 – 315 K and at frequencies up to 12 GHz. At low frequencies P3HT shows a semi-conducting character and the overall dielectric response is dominated by dc-conductivity with the activation energy of about 17 kJ/mol. The apparent semi-conducting character cease above certain critical frequency above which, the material becomes a dielectric. At room temperature the semi-conducting to dielectric transition takes place at about 5 kHz. Consequently, the practical applications are limited to this frequency. In the frequency range of 10 kHz to 12 GHz the dielectric dispersion is insignificant and the dielectric constant is about 4. The identified dielectric relaxation can be attributed to local molecular motion of thiophene rings, with the relaxation time of 3 * 10 –5 s and the activation energies of about 24 kJ/mol. The observed dielectric process reveals a broad symmetric loss peak in the frequency domain, obeys the Arrhenius law and its dielectric strength increases with temperature, thus in the sense it is similar to b - relaxation observed in polymers.
Mentor: Jan Obrzut
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Poster Category: Materials