The Syntheses Of Novel End-functionalized Poly(3-alkylthiophene) And The Study Of Its End-on Orientaion In Organic Thin Film

Semiconducting polymer has gained serious attention in21stcentury due to its greatpotential to replace the inorganic electro-optic material. It not only owns the commonoptoelectronic properties, but also has the advantages of general polymer such as low price,power production, easy fabrication and high flexibility. Thus, semiconducting polymerpossesses a broad application range and a bright future. Nowadays the low efficiency ofpolymer device is the only obstacle for further development. According to relevant studies,the carrier transport process plays the most important role in both photovoltaic and lightemitting diodes. Unfortunately, mobility of polymer devices is just one percent whencompared to inorganic ones. Theoretically, the mobility could be much higher when thecarriers “drift” through the polymer backbone. Establishing a novel and better transportpath, which forces carrier to “drift” though the polymer main chain, could be a promisingmethod to improve the transport efficiency and to increase the mobility.Some of the polymers have the ability of crystallization and forming anisotropystructure. Controlling the orientation of highly anisotropic structures of polymers isimportant because the majority of their mechanical, electronic, and optical propertiesdepend on the orientation of the polymer backbone. In this study, we designed andsynthesized end-functional polymer, which combines the self-assemble property ofpolythiophene derivatives and the surface segregated property of fluoroalkyl groups. Itcould cause spontaneous self-segregation of the polymer to the surface of the polymer film.A highly ordered end-on orientation of conjugated polymer was observed, where thepolymer main chain perpendicular to the substrate plane. End-on orientation should bemuch more suitable to the device in which carrier transports also through the verticaldirection to the electrodes (i.e. polymer solar cells and light emitting diodes). It could bealso helpful to improve the charge transport efficiency and to increase carrier mobility inpolymer device. Besides that, end-on orientation has some unique optical properties.Thesis contains follow parts:1. A novel end-fluoroalkylated poly(3-butylthiophene)(P3BT-F) was successfullysynthesized. The primary structure of P3BT-F was confirmed by1H NMR spectroscopy,time-of-flight-mass spectrometry (MALDI-TOF MS), gelpermeation chromatography(GPC) and X-ray photoelectron spectroscopy (XPS). Synthesized P3BT-F had controllabledegree of polymerization, small polydispersity index and high convertion of end group. P3BT-F had the similar structure and opti-electical properties with P3BT, and the onlydifference between two is the ability of crystallization.2. The perfect end-on orientation was acchieved by using P3BT-F/PS (polystyrene)blend film. Inside crystal domain, over90%of the polymer was arranged in end-onorientation with only10°orientation distribution. The surface segregation of fluorocarbonchain was studied by X-ray photoelectron spectroscopy. We have established standardcharacterization method of end-on orientation, while studing the effect of molecularstructure. End-on orientation was investigated by UV-visible spectroscopy. This is the firstto report its unique optical properties.3. We first proved the possibility of inducing end-on orientation inside the film bulk bystudying P3BT-F/P3AT blended film. Further studies on this film were done by changingthe initial angle of grazing-incidence X-ray diffraction. Causing the similar structure, P3ATcould form co-crystal with P3BT-F and keep the end-on orientation. The effect offabrication process was well studied.4. The novel end-functionalized poly(3-butylthiophene) with thiol group (P3BT-S) wasused to form c.a.4.6nm thick P3BT-S self-assembled monolayers (SAMs) on gold surface.This P3BT-S SAMs could help change the orientation of polymer backbone at thepolymer/substrate interface. The P3BT-S base P3BT-F/P3BT blend film showed highend-on orientation fraction inside the crystal domain. The carrier mobility perpendicular tothe device of this film achieved quite high value of1.1×10-2cm2/Vs, which was an orderof magnitude higher than the mobility in ordinary P3BT film. Based on our knowledge，thisis the highest value among the semiconducting polymer materials. Through the study ofcrystal structure and electrical properties of this sandwich film, the relationship betweenpolymer chain orientation and carrier mobility was unveiled.