Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)


Electrical and Computer Engineering (Holcomb Dept. of)

Committee Chair/Advisor

Dr. William R. Harrell

Committee Member

Dr. Igor Luzinov

Committee Member

Dr. Goutam Koley

Committee Member

Dr. Judson Douglas Ryckman


An original design and photolithographic fabrication process for poly(3-hexylthiophene-2, 5-diyl) (P3HT) based organic thin-film transistors (OTFTs) is presented. The structure of the transistors was based on the bottom gate bottom contact OTFT. The fabrication process was efficient, cost-effective, and relatively straightforward to implement. Current–voltage (I-V) measurements were performed to characterize the primary electronic properties of the transistors. The measured mobility of these transistors was significantly higher than most results reported in the literature for other similar bottom gate bottom contact P3HT OTFTs. The higher mobility is explained primarily by the effectiveness of the fabrication process in keeping the interfacial layers free from contamination, as well as the proper annealing of the P3HT.

An interface engineering method is investigated to further enhance the performance of the OTFTs. Three interfacial materials were used for this purpose: graphene oxide (GO), poly(oligo (ethylene glycol) methyl ether methacrylate- glycidyl methacrylate- lauryl methacrylate) (P(OEGMA-GMA-LMA)) or POGL, and a composite of GO and P(OEGMA-GMA-LMA) or GO-POGL. The OTFTs with a GO interfacial layer were observed to have a higher drain current and field-effect mobility than the OTFTs with no interfacial layer. The enhanced drain current and mobility are associated with the particular structure of the P3HT layer on the dielectric surface and the reduction in the contact resistance between the GO-covered electrodes and the P3HT. The OTFTs with a POGL interfacial layer were observed to have a smaller threshold voltage than the OTFTs with no interfacial layer. The POGL OTFTs were also observed to have much more ideal drain current saturation characteristics with very small I-V curve slope. This is explained by the deep trap states on the POGL surface and the reduction of the contact resistance at the electrode/organic semiconductor interface. The OTFTs with a GO-POGL composite layer were observed to have a higher drain current and mobility, and a smaller threshold voltage than the OTFTs without an interfacial layer, which is the optimum case for these two device parameters. The higher drain current and field-effect mobility are attributed to the larger interconnecting grains of the P3HT that is deposited onto the GO-POGL surface and the smaller interfacial tension between the GO-POGL and the P3HT. The smaller threshold voltage is attributed to the deep trap states on the GO-POGL layer and the smaller contact resistance between the GO-POGL modified electrodes and the P3HT. Furthermore, experiments that could be performed to advance this research work and enhance the performance of the OTFTs even further are proposed.

Author ORCID Identifier




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