Abstracts Category : Other

Controlling the Orientation of Semiconducting Polymers in Floating Film for Anisotropic Charge Transport in Organic Field Effect Transistor :

by Manish Pandey

Conjugated polymers (CPs) are among the most investigated semi-conducting material for their potential application in next generation electronic devices by roll-to-roll printing technique such as thin film transistors, photovoltaics, light emitting diodes etc. The performance of the any CP depends on the ease with which charge carriers can be transported in them. Although in the past two decades extensive research has been done by the scientific community to understand the charge transport mechanism in CPs, consensus have been well established that that morphology of CP in their thin films serves as the deceive parameter which influences the device parameter. In this perspective, orienting CPs in one direction has been focal point of many researchers to improve the overall device performance. This thesis presents a detailed investigation of orientation characteristics in a newly developed method for fabrication of oriented thin films named floating film transfer method (FTM). The orientation characteristics of some of well-known CPs such as Non-regiocontrolled poly(3-hexylthiophene) (NR-P3HT), Regioregular poly(3-hexylthiophene), Poly(3,3???-didodecyl-quarterthiophene), Poly[2,5-bis(3-tetradecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT), Poly(9,9-dioctylfluorene), and Poly(9,9-dioctylfluorene-alt-bithiophene) have been carried out by polarized absorption spectroscopy, atomic force microscopy, X-ray diffraction, polarized Fourier transform spectroscopy, polarized Raman spectroscopy. The influence the microstructures on the electrical parameters were investigated by fabricating thin film transistors. This investigation related to the orientation characteristics of CPs in FTM revealed that the casting conditions of the floating film on liquid substrate serves the most important role for optimizing the orientation intensity of individual CP. However, investigations revealed that the given polymer will only be able to orient if they are of liquid crystalline nature in particular lyotropic or thermotropic. Preliminary results observed by optimizing the orientation of one of the well-known amorphous NR-P3HT revealed very high orientation with nanofibrous domains. When the influence of these oriented domains on charge transport in transistors were studied they showed drastic enhancement of field effect mobility in comparison to isotropic films. A greater insight of orientation and charge transport was further investigated by blending amorphous NR-P3HT with crystalline material (PBTTT) in order to see changes in the orientation and their effect on charge transport. We have shown that that the orientation in oriented fibrous domain can be further enhanced by slight addition of the guest material, which results in to synergistic improvement of P a g e | 6 Kyushu Institute of Technology orientation as well as the mobility, which also revealed that the resulting orientation and mobility depends on the individual constituent. In order to extend the use of optimization techniques for orientation further, an air stable highAdvisors/Committee Members: Pandey, Shyam sudhir.