Browsing by Author "Barron, Andrew R"
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Item All-Conjugated Block Copolymers for Organic Photovoltaics(2015-04-20) Lin, Yen-Hao; Verduzco, Rafael; Wong, Michael S; Barron, Andrew ROrganic photovoltaics (OPVs) are a promising source of alternative energy due to cost effectiveness and process simplicity. However, the performance of OPVs must be improved to produce viable devices. This can be achieved by optimizing the optoelectronic properties of constituent materials, tuning the nanostructures of materials within active layer of OPVs and defining a well-defined interface between electron-donor materials and electron-acceptor materials. The above opportunities can potentially be addressed with using all-conjugated block copolymers in that self-assembly of block copolymers can lead to well-defined nanostructures driven by thermodynamics. The focus of this thesis is on the synthesis and development of all-conjugated block copolymers in which one block is an electron-donor polymer and the other is an electron-acceptor polymer. We focus primarily on poly(3-hexylthiophene) (P3HT)-based block copolymers in which the electron-donor P3HT is made from Grignard metathesis polymerization (GRIM) and the other block is synthesized by Suzuki-Miyaura polycondensation reaction for wide variety of electron-acceptor polymers. Subsequently, the nanostructures of polymers were studied on a model series of all-conjugated block copolymer: poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene) (P3HT–b–PF) under different processing conditions with using differential scanning calorimetry (DSC) and grazing-incidence X-ray scattering (GIXS). This reveals strong process-structure-property relationships of all-conjugated block copolymers. Furthermore, using our two-step synthetic route, we prepared an all-conjugated block copolymer poly(3-hexylthiophene)—block—poly[2,7-(9′,9′-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3′,-benzothiadiazole)] (P3HT–b–PFTBT) that exhibits over 3% PCEs as the active layer in a solution processed OPV due to the formation of lamellae of the block copolymers and preferential π-π stacking direction of the P3HT perpendicular to the substrate. In addition to covalently linked block copolymers, we applied a quadruple hydrogen group, 2-ureido-4[1H]-pyrimidinone (UPy), as polymeric end functionalities to reduce macro-phase separation in polymer blends. In the polymer blends OPVs comprised of P3HT and PFTBT, the UPy hydrogen bonding group reduces macro-phase separation in polymer blends and leads to improved power conversion efficiency of OPVs from 0.43% to 0.77% under 155 oC annealing condition. This thesis demonstrates that both the covalently linked and hydrogen bonding linked all-conjugated block copolymers are potential to enhance performance of OPVs. Furthermore, with the advancement in synthetic techniques and better understandings on structure-processing-property relationships of all-conjugated block copolymers, we are able to apply those into more emerging conjugated polymers and engineer molecules for efficient energy generation in OPVs.Item An Investigation of Carbon-based Nanomaterials for Efficient Energy Production and Delivery(2016-01-28) Gangoli, Varun Shenoy; Wong, Michael S.; Pasquali, Matteo; Barron, Andrew R; Adams, Wade; Hauge, Robert HCarbon-based nanomaterials have been demonstrated to have different potential applications in the energy industry. However, there are challenges in the realization of these applications. Chirality of single wall carbon nanotubes (SWCNTs) defines their electronic properties, and obtaining an ensemble of SWCNTs of the same chirality has been a problem studied for over two decades with no clear solution yet. Other carbon-based nanomaterials, such as carbon black aggregates, are hydrophobic in nature and potential applications in the oil and gas industry require their dispersal in an aqueous solvent. Another application in the oil and gas industry is enhanced oil recovery (EOR), and here there is a need for an inexpensive, stable, and efficient surfactant compared to currently used industrial solutions. The challenge of producing SWCNTs of the same chirality is studied using two approaches- separation after synthesis of SWCNTs of mixed chiralities, and chemical control over chirality of as-synthesized SWCNTs. Agarose gel-based affinity chromatography was used as a means towards highly semiconductor- enriched SWCNTs using a family of nonionic surfactants. UV-vis-NIR spectroscopy, Raman spectroscopy and photoluminescence spectroscopy was used to quantify the separation efficiency of the metal- and semiconductor-enriched SWCNTs. This process is an improvement over other chromatography-based techniques at the time in that the nonionic surfactants used are less expensive, enable a higher purity of semiconductor SWCNTs (>95%) and decompose fully by simply heating in air thus leaving behind pristine SWCNTs. The second approach was based on using catalyst dopants to preferentially synthesize SWCNTs of a particular chirality at the expense of SWCNTs of other chiralities. Heterogeneous catalysis combined with the screw dislocation theory of SWCNT growth provided the background for this work, and both selenium and phosphorus were identified as chemical dopants for iron catalysts. Both selenium and phosphorus were demonstrated to have a direct effect on the average number density and length of SWCNTs, and selenium also was shown to have a direct control over the growth rate of SWCNTs. This, combined with some preliminary spectroscopy results, suggest chiral control over the carbon nanotubes. Collaborative work on phase transfer of hydrophobic carbon-based nanomaterials into aqueous solvents for applications including saturated oil residual (SOR) detection and quantification in underground reservoirs helped recognize the potential of hydrophobically modified polymers as surfactants for EOR. Polystyrene sulfonate was chosen as the polymer of study owing to ease of availability, low cost of the precursor material and aromatic sulfonates already being studied for EOR. Controlled desulfonation of PSS was achieved by rapid heating of an aqueous solution of PSS in a microwave reactor under acidic conditions, with the reactant temperature and pH having a strong effect on the degree of desulfonation of the product ranging from 4.9% (as-obtained PSS) to 40%. Dynamic light scattering of the desulfonated PSS (termed PDS) in brine showed good stability of the polymer aggregates at temperatures as high as 150 ºC, and tensiometry with aromatic oils such as toluene and aliphatic oils such as Isopar L showed good surface activity with interfacial tension going as low as 10-2 mN/m. Breakthrough experiments with sand packed columns at the lab scale, and core flooding at an independent facility confirmed good propagation of PDS through materials such as Berea sandstone, with minimal plugging and adsorption losses.Item Coating and Doping of Ge QDs(2016-01-14) Oliva-Chatelain, Brittany Lynn; Barron, Andrew R; Billups, W. E.; Verduzco, RafaelThe ability to incorporate a dopant element into nanocrystals (NCs) and quantum dots (QDs) is one of the key technical challenges for the use of these materials in a number of optoelectronic applications, particularly solar applications. Unlike doping of traditional bulk semiconductors materials, the location of the doping element can be either within the crystal lattice (c-doping), on the surface (s-doping), or within the surrounding matrix (m-doping). A range of attempts to dope Ge QDs both during and post-synthesis are reported here. The QDs have been characterized by TEM, XPS, and I/V measurements of SiO2 coated QD thin films in test cells using doped Si substrates. The solution synthesis of Ge QDs by the reduction of GeCl4 with LiAlH4 results in Ge QDs with a low level of chlorine atoms on the surface; however, during the H2PtCl6 catalyzed alkylation of the surface with allylamine, chlorine functionalization of the surface occurs resulting in p-type doping of the QD. A similar location of the dopant is proposed for phosphorus when incorporated be the addition of PCl3 during QD synthesis; however, the electronic doping effect is greater. The detected dopants are all present on the surface of the QD (s-type), suggesting a self-purification process is operative. Attempts to incorporate boron or gallium during synthesis were unsuccessful. The silica coating of these particles was successful using a modified Stöber method. Monodispersed silica nanoparticles 20 nm in diameter were synthesized with Ge QDs as seeds. The resulting structures comprise of Ge QD core within a silica sphere. Films of these particles result in an average QD…QD distance of 9.6 nm, which is less than the maximum distance required for good electron transfer (10 nm). Film thickness and annealing tests were done to optimize the cells. These cells were tested for efficiency, and it was found that the phosphorus doped quantum dots and the undoped quantum dots both produced the highest photo induced current on n-type silicon wafers at ¼ of the maximum concentration of these particles with the phosphorus doped quantum dots producing a higher efficiency overall. Thermal annealing the films prior to deposition of the front and back contacts enabled a doubling in the cell efficiency, but did not show any marked increase in the density or crystallinity of the films.Item Metal ferrite nanoparticles as tracers in hydraulically fractured wells(2015-02-27) Morrow, Lauren; Barron, Andrew R; Wilson, Lon J; Pasquali, MatteoA variety of metal ferrite nanoparticles were synthesized via thermal decomposition reaction and characterized with transmission electron microscopy, small angle X-ray scattering, inductively coupled plasma – optical emission spectroscopy, X-ray photoelectron spectroscopy, thermogravimetric analysis, and a superconducting quantum interference device in order to develop a cost-effective means of tracing hydraulic fractures in wells. In addition, the nanoparticles were developed as a means of determining sources of contamination in the environment surrounding a well by way of “fingerprinting” the different potential sources. This is achieved through the manipulation of the quantities of metal cations substituted into the crystal structure of magnetite, allowing for the creation of unique and desired magnetic characteristics. In order to determine the feasibility of using nanoparticles as tracers, the quantity needed to be able to detect the nanoparticles as determined, as well as how the magnetic properties change as temperature increases as a function of nanoparticle composition. Finally, the feasibility of making industrial quantities of the nanoparticles was investigated.Item Synthesis of black silicon anti-reflection layers for silicon solar cells(2015-04-23) Lu, Yen-Tien; Barron, Andrew R; Biswal, Sibani L; Verduzco, RafaelSolar energy is one of the most important renewable energy resources in the world. Among all kinds of solar cells, the fabrication technology of silicon solar cells is relatively mature which makes them more popular in the solar cell market. However, in order to compete with the traditional energy sources, decreasing cost of per watt output seems necessary. Hence, increasing the energy conversion efficiency with an economical approach is an unavoidable issue. One solution is applying anti-reflection layers onto the silicon solar cells to maximize energy conversion efficiency. Recently, black silicon anti-reflection layers have attracted attention because their anti-reflection ability is less confined by the incident light angle and wavelength. In this thesis, two methods, the metal-assisted chemical etching and the contact-assisted chemical etching method, which have potential to economically fabricate large-scale black silicon on silicon solar cells are systematically studied. The complete etching mechanisms of these two methods are also proposed to clearly describe the fabrication process of black silicon.