<p> Solar radiation is a vast, distributed, and renewable energy source which Humanity can utilize via the photovoltaic effect. The goal of photovoltaic technology is to minimize the true costs, while maximizing the power conversion efficiency and lifetime of the cell/module. Interface-related approaches to achieving this goal are explored here, for two technologically-important classes of light absorbers: crystalline-silicon (c-Si) and metal halide perovskite (MHP). The simplest solar cell consists of a light absorber, sandwiched between two metals with dissimilar work functions. Carrier-selective contacts (CSC&rsquo;s), which are ubiquitous in modern solar cells, are added to improve the electrical performance. Solar cells require asymmetric carrier transport within the cell, which can be effected via electrostatic and/or effective fields, and CSC&rsquo;s augment the asymmetry by selectively transporting holes to one contact, and electrons to the other contact. </p><p> The proper design and implementation of a CSC is crucial, as the performance, lifetime, and/or cost reduction of a solar cell can be hampered by a single interface or layer. A framework, consisting of eight core requirements, was developed from first-principles to evaluate the effectiveness of a given CSC. The framework includes some requirements which are well-recognized, such as the need for appropriate band offsets, and some requirements which are not well-recognized at the moment, such as the need for effective valence/conduction band density of states matching between the absorber and CSC.</p><p> The application of the framework to multiple silicon-based and MHP-based CSC&rsquo;s revealed the difficulties of effectively designing and implementing a CSC. A poly(3-hexylthiophene)/c-Si heterojunction was found to be a near ideal hole-selective contact (HSC). Three metal oxide/c-Si heterojunctions initially expected to yield comparable electron-selective contacts (ESC&rsquo;s), titanium dioxide/c-Si (TiO₂/c-Si), zinc oxide/c-Si (ZnO/c-Si), and tin dioxide/c-Si (SnO₂/c-Si), were instead discovered to be widely different. The TiO₂/MHP heterojunction was found to be a moderately ideal ESC, and the nickel oxide/MHP (NiOX/MHP) heterojunction is expected to be a good HSC. If interfacial lead di-iodide (PbI₂) is intentionally or unintentionally deposited at the interfaces of a MHP solar cell, it is expected to be detrimental to the operation of the NiOX/MHP HSC, but not to the TiO₂/MHP ESC.</p><p>

The assembly of nanoparticles at the interface of immiscible fluids holds promise for the preparation of new materials that benefit from both the physical properties of the nanoparticles and the chemistry associated with the ligands. Shaking nanoparticle solutions in organic solvents with water, results in the formation of nanoparticle-coated droplets that range in size from 10 µm to 200 µm. A strategy to control the size of these emulsions is described, by passing the droplets through commercial track-etch membranes with known pore sizes. Extrusion reduces the droplet size by breaking the droplets while passing theough the membrane pores, and reforming in the presence of excess nanoparticles in solution to form droplets as small as 1-5 µm. Crosslinking of nanoparticles at a liquid interface lends greater stability to the interfacial assembly, leading to ultrathin nanoparticle-based capsules, which possess mechanical integrity even after removal of the interface. Two approaches towards crosslinking are used in this thesis. Norbornene-functionalized CdSe/ZnS are used to afford facile capsule visualization by fluorescence confocal microscopy, as well as ease of crosslinking in mild conditions by means of ring-opening metathesis polymerization (ROMP). The crosslinked capsules can be used to encapsulate materials, and display size-selective retention capability, governed by the interstitial spaces between the nanoparticles. In a second approach to making hybrid capsules and sheets, horse spleen ferritin bionanoparticles and aldehyde-functionalized CdSe quantum dots are co-assembled at an oil-water interface. The cross-linked materials formed by reaction of the aldehyde functionality on the quantum dots with the surface-available amines on the ferritin bionanoparticles can be disrupted by addition of acid, thus leading to pH-degradable capsules and sheets. The driving force for assembly of nanoparticles at liquid interfaces is the reduction of the interfacial energy between the two liquids. The factors governing the amount of interfacial stabilization provided by the nanoparticles, namely the size and ligand coverage of the nanoparticles, are examined using the example of mixed assemblies of two different types of nanoparticles. Assemblies of 10 nm cobalt nanoparticles are disrupted upon the addition of 2.5 nm CdSe nanoparticles. The studies in this thesis demonstrate that the lower density of ligand coverage on CdSe quantum dots can overcome the large difference in size between the two nanoparticles, thus displacing the cobalt nanoparticles from the interface. Finally, preliminary results using amphiphilic graft copolymers instead of nanoparticles for interfacial stabilization of liquids are discussed. The resulting capsules are used for encapsulation and release of nanoparticles. In a technique termed repair-and-go, these nanoparticle-filled capsules are used for repairing cracked surfaces by passing the capsules over hydrophilic substrates containing hydrophobic cracks.

Anhydrous proton conducting polymers are highly sought after for applications in high temperature polymer electrolyte membrane fuel cells (PEMFCs). N-heterocycles (eg. imidazole, triazole, and benzimidazole), owing to their amphoteric nature, have been widely studied to develop efficient anhydrous proton transporting polymers. The proton conductivity of N-heterocyclic polymers is influenced by several factors and the design and development of polymers with a delicate balance among various synergistic and competing factors to provide appreciable proton conductivities has been a challenging task. In this thesis, the proton transport (PT) characteristics of polymers functionalized with two diverse classes of functional groups— N-heterocycles and phenols have been investigated and efforts have been made to develop the molecular design criteria for the design and development of efficient proton transporting functional groups and polymers. The proton conduction pathway in 1H-1,2,3-triazole polymers is probed by employing structurally analogous N-heterocyclic (triazole, imidazole, and pyrazole) and benz-N-heterocyclic (benzotriazole, benzimidazole, and benzopyrazole) polymers. Imidazole-like pathway was found to dominate the proton conductivity of triazole and pyrazole-like pathway makes only a negligible contribution, if any. Polymers containing benz-N-heterocycles exhibited higher proton conductivity than those with the corresponding N-heterocycles. Pyrazole-like functional groups, i.e. the molecules with two nitrogen atoms adjacent to each other, were found not to be good candidates for PT applications. A new class of proton transporting functional groups, phenols, has been introduced for anhydrous PT. One of the highlighting features of phenols over N-heterocycles is that the hydrogen bond donor/acceptor reorientation can happen on a single -OH site, allowing for facile reorientational dynamics in Grotthuss PT and enhanced proton conductivities in phenolic polymers. Unlike the case of N-heterocycles, comparable conductivities were achieved between poly (3,4,5-trihydroxy) styrene and the corresponding small molecule, pyrogallol. This observation suggests that reorientation should be considered as a crucial design parameter for PT functional groups. The PT characteristics of phenol-based biaryl polymers are studied and compared with the analogous phenol-based linear styrenic polymers. The two-dimensional disposition of -OH moieties in biaryl polymers, although resulted in lower apparent activation energies (Ea), did not improve the net proton conductivity due to the accompanying increase in glass transition temperature (Tg). Thus, the ease of synthesis and lower Tg values of phenol-based styrene polymers make the styrenic polymer architecture preferable over the biaryl architecture. Finally, the synthesis of a series of poly(3,4-dihydroxy styrene)-b-polystyrene block copolymers has been demonstrated via anionic polymerization. These block copolymers will provide an opportunity to systematically investigate the effect of nanoscale morphology on proton transport.

Supramolecular chemistry is the study of discreet molecules assembled into more complex structures though non-covalent interactions such as host-guest effects, pi-pi stacking, electrostatic effects, hydrogen bonding, and metal-ligand interactions. Using these interactions, complex hierarchical assembles can be created from relatively simple precursors. Of the supramolecular interactions listed above, metal-ligand interactions are of particular interest due to the wide possible properties which they present. Factors such as the denticity, polarizability, steric hindrance, ligand structure, and the metal used (among others) contribute to a dramatic range in the physical properties of the metal-ligand complexes. Particularly affected by these factors are the kinetic and thermodynamic properties of the complexes. As a result metal-ligand interactions can vary from inert to extremely transient. Of the vast number of ligands available for study, this dissertation will center on substituted terpyridine ligands, with a particular focus on terpyridine-functionalized polymers. While polymer-functionalized terpyridine ligands and their complexes with transition metals have been heavily studied, the physical properties, particularly the effects of polymer functionalization on the stability of bis complexes of terpyridines, remain unexplored. In the course of investigating the kinetic stability of these complexes, polymer functionalization techniques were developed which were found to increase the stability of the metal-ligand interactions compared to conventional techniques. In addition to studying the effect of terpyridine substituents, the effects of solvent on the stability of the complexes was studied as well. As polymer-bound terpyridine complexes are often studied in solvents other than water, knowledge of the stability of the complexes in organic solvents is important to create supramolecular structures with more precisely controlled properties. It was found that, for unsubstituted terpyridyl complexes, the stability of the complexes varied by as many as five orders of magnitude in common solvents. It is believed that this decrease in stability is the result of the ability of the solvent to facilitate the movement of the ligands from the first and second coordination spheres. Although a large part of this dissertation is dedicated to the study of the kinetic stability of terpyridine complexes, synthetic techniques involving terpyridine and its complexes were investigated as well. It was found that terpyridine functionalized polystyrene could be produced by direction functionalization of terpyridine with polystyryllithium. Additionally heterloleptic terpyridine-based iron complexes were produced with high purity by reduction of the mono terpyridine complex of iron(III) in the presence of a second, functionalized terpyridine ligand. The culmination of these studies was the synthesis of supramolecular organogels, which were crosslinked using metal-terpyridine complexes, yielding dynamic mechanical properties could be broadly tuned by varying the metal used to form the crosslinks.

All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.

The work in this dissertation is divided into two distinct projects. The majority of this dissertation was based on applications of planar and patterned metal oxide nanocomposites; in particular modifying the properties of both polymer nanocomposites and all inorganic nanocomposites. A series of nanocomposites were generated to modify the refractive index or dielectric constant of these materials. Three applications were developed for the material systems created. The first was a high dielectric constant (k) layer that was used to generate all solution processable OFETs. Next, a novel strategy was created for patterning metal oxide nanoparticle nanocomposites, by using a form of solvent assisted nanoimprint lithography, which had previously only been adapted for metal nanoparticles. This simple and straightforward approach was used for a number of different nanoparticle systems, titanium dioxide (TiO2), cerium dioxide (CeO2), zirconium dioxide (ZrO2), iron oxide (Fe2O3), and indium doped tin oxide (ITO), along with either organic or inorganic based binders. These nanocomposites were then developed to generate high surface area doped solid oxide fuel cell electrolytes. Finally, the first known all solution processable log-pile 3D photonic crystal was created, by using a high refractive index TiO2 nanocomposite. A transfer printing technique was invented to use a layer-by-layer strategy to generate a 6-layer 3D photonic crystal that was able reflect over 70% of the incident electromagnetic spectrum at 1000 nm. The second project developed a reactive polymer blend that was used as for CO2/N2 gas separations. The polymer blend was based on commodity scale block copolymers, Pluronic® (poly(ethylene oxide )-b-poly(propylene oxide)-b-poly(ethylene oxide), PEO-b-PPO-PEO) which are phase separated in the melt. The block copolymer becomes phase separated upon the addition of a hydrogen bond donating polymer, in this case a polyimide precursor, poly(amic acid) (PAmA), which was synthesized from pyromellitic dianhydride and 4, 4'-oxydianiline (PMDA-ODA PAmA). These blends were shown to favorably interact due to the amide and carboxylic acid groups present on the PMDA-ODA PAmA. The PMDA-ODA PAmA can be thermally imidized, while maintaining order and the ideal gas permeation properties were investigated to determine the likelihood of these blends to be used for commercial gas separation membranes.

Three new strategies were successfully pursued for the synthesis of defined length oligomers of p-phenylene-vinylene. These strategies are interchangeable and allow the fast and efficient synthesis of a wide variety of oligomers with a number of different substituents. An assortment of new molecules and oligomers were synthesized and characterized during this study to prove the effectiveness of each strategy. The new strategies were compared to previous methodology for making similar oligomers. A large, nonplanar, conjugated chromophore 9BrH was synthesized based on an adaptation of previous work. 9BrH and its synthetic precursor, pre9BrH, were characterized using X-Ray crystallography. The experimentally determined conformation and bond lengths of 9BrH were compared to previous theoretical studies and confirmed much of what was predicted. The 9BrH chromophore was stockpiled for use in additional studies. Three highly twisted triarylamines were synthesized and investigated for internal charge transfer behavior. Using a large chromophore as one aryl group forced the triarylamines into twisted, propeller-like conformations. The chromophore anthracene was utilized to induce the twist in the triarylamines 9DAAA and 910BAA. The previously synthesized 9BrH was utilized to induce a twisted conformation for the triarylamine 9DAAH. Theoretical predictions indicated that electron density should be delocalized in the ground state and localized on the large chromophore in the excited state, behavior consistent with molecular internal charge transfer. 9DAAA and 910BAA were characterized by X-Ray crystallography which confirmed the desired twisted conformation of the triarylamines in the solid state. UV-Vis absorption spectra for all three triarylamines had long wavelength, broad absorption peaks characteristic of internal charge transfer. Solution fluorescence of each triarylamine demonstrated a large dependence on the surrounding environment; when solvent polarity was increased, fluorescence intensity decreased and red shifted. This behavior was also attributed to interactions between the strong dipole of the triarylamines in the excited state with the dipole of solvent molecules in the surrounding environment. Fluorescence lifetime studies allowed the derivation of a model in which the triarylamines had two different, competing decay pathways from the ground state to the excited state. The aggregation properties of 9DAAA were studied using binary solvent mixtures which forced dissolved 9DAAA from the solution. Suspensions of aggregates of 9DAAA were found to have enhanced emission properties up to 700% more intense than solutions of 9DAAA. This behavior was attributed to the change in surrounding environment of 9DAAA when switching from dissolved to aggregated. The polar solvent surrounding fully dissolved 9DAAA suppresses fluorescence while the solid-state environment of 9DAAA upon aggregation allows decay from the excited state to the ground state to occur via fluorescence. 9DAAA and 910BAA were characterized by cyclic voltammetry which indicated that their energy levels fell between two commonly used components of dye sensitized solar cells. Studies were done to evaluate the effect of triarylamine additives to the redox couple solution of dye sensitized solar cells. Both triarylamines improved the performance of the cells to which they were added; 9DAAA improved the cells' VOC parameter while 910BAA improved the cells' JSC parameter. These studies suggest that 910BAA actively participates in electron shuttling between a cell's redox couple and dye.

The highly ordered long range structure associated with the crystalline core of semi-crystalline linear aliphatic polyesters, is evaluated using Raman spectroscopy. Polarization modulation reflection infrared spectroscopy, and x-ray photoelectron spectroscopy, are utilized to determine the degree of structural and chemical anisotropy in ultra thin glassy polymer films formed by monolayer chemisorption of functionalized polystyrene onto external surfaces. In both cases the morphological characterization is restricted to the determination of polymer structure in regions that are on the order of 100 angstroms or less in thickness. The frequency of the longitudinal acoustic mode (LAM-1) normal mode vibration is inversely related to the crystal stem length. It is found in the very low frequency region of the Raman spectrum for these linear aliphatic polyesters. It is utilized to directly determine the crystal thickness, the distribution of crystal stem lengths, and the longitudinal Youngs modulus. The existence of multiple low frequency components is studied as a function of degree of supercooling, monomer chemical structure, crystal packing, and crystal thickening. Polarization modulation reflection infrared measurements, and a segmental orientation model based solely upon relative intensities, are used to determine the average chain axis orientation relative to the surface normal for sulfur functionalized polystyrenes adsorbed to Au surfaces. The orientation of the polystyrene chain is higher for the PS$\sb{95}$-PPS$\sb5$ adsorbed film (0.29) than for the thiol endcapped polystyrene (0.22). The higher copolymer orientation can be attributed to the slightly longer strongly interacting part of the structure. The block is sufficiently long to enable a higher grafting density. Results for other copolymers indicate that a structural transition occurs in the adsorbed copolymer films between 95:5 and 90:10 molar ratios, for a degree of polymerization around 600. The transition from anisotropic to an isotropic polystyrene conformation is related to the XPS film thickness, and thus the grafting density. Segregation in the chemical composition exists as shown by XPS. The degree of segregation is related to the propylene sulfide block length relative to the overall degree of polymerization. If the interaction strength is sufficiently large then a critical block length will exist which will determine whether the buoy structure can form an oriented brush in solution and a collapsed oriented ultra thin film.

Hierarchically structured inorganic materials are everywhere in nature. From unicellular aquatic algae such as diatoms to the bones and/or cartilage that comprise the skeletal systems of vertebrates. Complex mechanisms involving site-specific chemistries and precision kinetics are responsible for the formation of such structures. In the synthetic realm, reproduction of even the most basic hierarchical structure effortlessly produced in nature is difficult. However, through the utilization of self-assembling structures or "templates", such as polymers or amphiphilic surfactants, combined with some favorable interaction between a chosen inorganic, the potential exists to imprint an inorganic material with a morphology dictated via synthetic molecular self-assembly. In doing so, a very basic hierarchical structure is formed on the angstrom and nanometer scales. The work presented herein utilizes the self-assembly of either surfactants or block copolymers with the desired inorganic or inorganic precursor to form templated inorganic structures. Specifically, mesoporous silica spheres and copolymer directed calcium phosphate-polymer composites were formed through the co-assembly of an organic template and a precursor to form the desired mesostructured inorganic. For the case of the mesoporous silica spheres, a silica precursor was mixed with cetyltrimethylammonium bromide and cysteamine, a highly effective biomimetic catalyst for the conversion of alkoxysilanes to silica. Through charge-based interactions between anionic silica species and the micelle-forming cationic surfactant, ordered silica structures resulted. The incorporation of a novel, effective catalyst was found to form highly condensed silica spheres for potential application as catalyst supports or an encapsulation media. Ordered calcium phosphate-polymer composites were formed using two routes. Both routes take advantage of hydrogen bonding and ionic interactions between the calcium and phosphate precursors and the self-assembling copolymer template. Some evidence suggests that the copolymer morphology remained in the composite despite the known tendency for calcium phosphates to form highly elongated crystalline structures with time, as is commonly the case for synthetic hydroxyapatites. Such materials have obvious application as bone grafts and bone coatings due, in part, to the osteoconductive nature of calcium phosphate as well as to the mesoporosity generated through the cooperative assembly of the block copolymer and the inorganic. Future work, including potential experiments to determine osteoconductivity of as-prepared composites, is also presented herein.

Nanoparticles made from platinum-group metals (PGMs) have demonstrated effectiveness as inorganic, artificial peroxidase mimics. These artificial enzymes boast several advantages over natural peroxidases, including superior catalytic efficiency, chemothermal stability, and cost effectiveness. PGM nanoparticles are therefore increasingly coming into use over protein-based enzymes across a variety of sectors, including public health, medical diagnostics, environmental protection, and automotive manufacturing. However, the full range of PGM nanoparticles with potential for these applications have not yet been systematically compared. Such a comparison will be significantly beneficial to future design of PGM nanoparticles, and their optimization as catalysts for industry. The present study aims to address this need through the systematic characterization and analysis of one type of PGM nanoparticle. Research of this type will greatly improve the future effectiveness of similar particles within their respective applications. In particular, this work focuses on palladium (Pd), a metal with an extensive history of use as an inorganic catalyst of organic reactions. The first phase of the study focuses on development of a reliable method for synthesis of Pd nanoparticles smaller than 10 nm, beginning with accepted procedures for the development of similar particles. The second involves a thorough characterization of the particles, using X-ray photoelectron spectroscopy (XPS) for elemental composition, transmission electron microscopy (TEM) for morphology, X-ray diffraction (XRD) for confirmation of surface facets, infrared spectroscopy (IRS) for confirmation of citrate surface ligand, and high-resolution TEM for single crystal structure. In the third phase, the particles will be tested for catalytic activity as artificial peroxidases in the oxidation of 3,3’,5,5’-tetramethylbenzadine (TMB) by hydrogen peroxide.