Thiophene-based all conducting block copolymers

Abstract

Block copolymer is one of the materials to control polymeric properties in nano-scale. Especially, GRIM polymerization is the method capable to make all conducting block copolymers and control their properties. In the optimization of this, almost monodisperse block copolymers could be synthesized, which would be the promising materials for the nanotechnology of electronic devices such as OTFTs, sensors, and photovoltaic devices. In addition, the new-type of the one-pot block copolymerization could be suggested with more functionalities of the control of the nano-scaled charge transfer and the uniform coating ability on the substrates having complicated shapes. PEP method was considered for the platform toward the one-pot block copolymerization. This allowed to coat on complicated-shaped substrates like mesoporous metal oxides. From this method, molecular weights, functionalities, and uniform coating on complicated-shaped substrates were performed. In the application of electronic devices having heterogeneous interface, we could observe the charge transfer characteristics with all conducting block copolymers at the p-n junction. In Chapter 2, A series of amphiphilic poly(3-hexylthiophene-b-3-(2-(2-{2-[2-(2-methoxy-ethoxy)-ethoxy]-ethoxy}-ethyl))thiophene) (P(3HT-b-3EGT)) polymers was synthesized via a nickel-catalyzed quasi-living polymerization. Size exclusion chromatograms (SEC) revealed that the molecular weight distributions of the P3HT blocks in the block copolymers were comparable with those of the polystyrene standard (monodisperse). 1H-NMR spectra revealed that the P3HT and PEGT units in the block copolymers were well-defined and did not form compositionally mixed regions at the boundary between the blocks and the highly regioregular P3HT units. The correlations among the block ratio, the amphiphilicity, and the self-assembled nanostructures of the block copolymers in thin films and in solution were examined. Differential scanning calorimetry (DSC) and X-ray diffraction (XRD) studies revealed that the crystallinity of the BP93 composed of 93 mol% P3HT blocks was higher than the crystallinity of the P3HT alone due to the packing effects caused by repulsion among the hydrophobic hexyl and hydrophilic ethylene glycol oligomer side chains. A long relaxation time was required to observe the ordering among P3HT blocks in the BP26 composed of 26 mol% P3HT blocks, suggesting that self-assembly could occur if induced on the molecular level. We demonstrated that the molecular-level self-assembly of BP26 (at dilute concentrations) via a slow dialysis method produced highly ordered polymer vesicles 200–250 nm in size under thermodynamic control. The size could be tuned via competitive hydrophobic interactions using polystyrene. In contrast, kinetic control via a rapid precipitation method yielded 5–20 nm micelles. In Chapter 3, A block copolymerization of non-functionalized conducting monomers was developed to enable the successful synthesis of a highly insoluble 3,4-(ethylenedioxy)thienyl-based all-conducting block copolymer (PEDOT-b-PEDOT-TB) that could encapsulate nanocrystalline dyed TiO2 particles, resulting in the formation of an all-conducting block copolymer bilayer hybrid nanostructure (TiO2/Dye/PEDOT-b-PEDOT-TB). Lithium ions were selectively positioned on the outer PEDOT-TB surface. The distances through which the positively charged dye and PEDOT-TB(Li+) interacted physically or through which the TiO2 electrode and the Li+ centers on PEDOT-TB(Li+) interacted ionically were precisely tuned and optimized within ca. 1 nm by controlling the thickness of the PEDOT blocking layer (the block length). The optimized structure provided efficient charge collection in an iodine-free dye-sensitized solar cell (DSC) due to negligible recombination of photoinduced electrons with cationic species and rapid charge transport, which improved the photovoltaic performance ( = 2.1 → 6.5 %). In Chapter 4, Synthesized monomers such as bis-EDOT-TBO3, bis-EDOT-TBO4, and bis-EDOT-TBO5 showed different lithium ion chelating properties. These resulted in non-chelating or chelating characters with Li+ concerned with the binding strength influencing the geometry of monomers during PEP. The polymers synthesized from monomers have different molecular weights (3,100 ~ 6800 Da) and conductivities (40 ~ 62 S/cm). We applied these polymers to the iodine-free sDSCs, which showed 3.0 ~ 5.2 % of PCE values depending on polymers such as PEDOT-TBO3, PEDOT-TBO4, and PEDOT-TBO5. The Li+ distribution in the devices and conductivities of polymers resulted in the variations of photovoltaic parameters. When we used PEDOT-TBO4, 5.1 % of PCE was achieved originated from higher JSC (11.4 mA/cm2). PEDOT-TBO5 based device showed 5.2 % of PCE resulted from higher VOC (0.83 V) with charge collection efficiency (90 %).