UNC-CH Physics and Astronomy Thesis Proposal Presentation

Zaf Jagoo

“Effects of Light, Bias Stress and Moisture on Organic Thin-Film Transistors”

Understanding the underlying physics of charge transport in organic semiconductors under different conditions is important for the development of applications exploiting the properties of organic semiconductors.The aim of this project is to investigate the effects of illumination on a bottom-gate bottom-contact diF-TES ADT thin-film transistor with visible light of different wavelengths and intensities. When the channel of the transistor was illuminated with visible light the output current increased due to exciton creation and dissociation and the transfer curves shifted to positive values, which was correlated with the absorption spectrum of the organic semiconductor. The number of photoinduced carriers measured was greater than what exciton generation alone could provide (η > 1). Two independent models of photogeneration from blocking contacts were devised to explain the observed phenomena. Photoresponsivities larger than 600mA/W were achieved for λ < 575nm, which exceeds the majority of organic and silicon photodetectors. The bias stress effect and device recovery were also studied by observing the shift of the transfer characteristic and the current change over long periods of time. Finally, the dependence of the electrical parameters of an organic transistor on the relative humidity was investigated. Device performance deteriorated when stressed and at higher levels of moisture.