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Title: Charge modulation spectroscopy of poly(3-alkylthiophene)
Author: Brown, P. J.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 2000
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Field-effect transistors with conjugated organic active layers are an attractive possibility for cheap, low-end, high volume electronics. Possible applications include identity tags or smart cards, however for this to become commercial reality the field-effect mobility of the charge carriers must be comparable to those in α:Si, around 0.1-1cm2/Vs. Short chain oligomers deposited by vacuum sublimation have been shown to satisfy this requirement, however this deposition technique is expensive and is therefore less attractive to industry. Conjugated polymers may be fabricated so that they may be cheaply cast from solution, however until recently these materials were considered to be poor candidates for these applications due to the disorder inherent in the deposited films resulting in mobilities as low as 10-4-10-3cm2/Vs. Recent advances in the fabrication of poly(3-hexylthiophene) (P3HT) have resulted in high field-effect mobilities of up to 0.1cm2/Vs due to inter-chain self-ordering between the polymer chains. This raises interesting questions as to the nature of the charge carriers in the film as in this transport regime the mobility of the charge carriers suggests that the traditional hopping transport of localised polaronic charge carriers may require modification. The topic of this thesis is the characterisation of the charge carriers in P3HT so that the high mobilities may be explained. The technique used to probe these characteristics is Charge Modulation Spectroscopy (CMS) which allows the phase sensitive detection of the optical absorption spectra of the field-induced charge carriers in P3HT to be studied in-situ. This is a powerful technique as it allows the spectra to be studied as a function of modulation frequency, temperature and charge density. The conclusion reached for P3HT is that the charge carriers are no longer localised onto one chain, as for other disordered polymers, rather they take on a delocalised two-dimensional character. As the degree of intra and inter-chain order is of great importance to the electrical characteristics of P3HT, the characteristics of these charge carriers were also studied as a function of polymer structural purity and side-chain length (from butyl to dodecyl).
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available