Hybrid TiO2 Solar Cells Produced from Aerosolized Nanoparticles of Water-Soluble Polythiophene Electron Donor Layer

Hybrid solar cells (HSCs) with water soluble polythiophene sodium poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate] (PTEBS) thin films produced using electrospray deposition (ESD) were fabricated, tested, and modeled and compared to devices produced using conventional spin coating. A single device structure of FTO/TiO2/PTEBS/Au was used to study the effects of ESD of the PTEBS layer on device performance. ESD was found to increase the short circuit current density (Jsc) by a factor of 2 while decreasing the open circuit voltage (Voc) by half compared to spin coated PTEBS films. Comparable efficiencies of 0.009% were achieved from both device construction types. Current-voltage curves were modeled using the characteristic solar cell equation and showed a similar increase in generated photocurrent with an increase by two orders of magnitude in the saturation current in devices from ESD films. Increases in Jsc are attributed to an increase in the interfacial contact area between the TiO2 and PTEBS layers, while decreases in Voc are attributed to incomplete film formation from ESD

Water Soluble Polymer Solar Cells from Electrospray Deposition

This dissertation reports the fabrication and characterization of thin films from the water soluble polymer sodium poly[2-(3-thienyl)-ethyloxy-4-butylsulfonate] (PTEBS) by electrospray deposition (ESD). Contiguous thin films were created by adjusting the parameters of the electrospray apparatus and solution properties to maintain a steady Taylor cone for uniform nanoparticle aerosolization and controlling the particle water content to enable coalescence with previously deposited particles. The majority of deposited particles had diameters less than 52 nm. A thin film of 64.7 nm with a root mean square surface roughness of 20.2 nm was achieved after 40 minutes of ESD. Hybrid Solar Cells (HSCs) with PTEBS thin films from spin coating and electrospray deposition (ESD) were fabricated, tested, and modeled. A single device structure of FTO/TiO2/PTEBS/Au was used to study the effects of ESD of the PTEBS layer on device performance. ESD was found to double the short circuit current density (Jsc) by a factor of 2 while decreasing the open circuit voltage (Voc) by half compared to spin coated PTEBS films. Comparable efficiencies of 0.009% were achieved from both device construction types. Current-Voltage curves were modeled using the characteristic solar cell equation showed a similar increase in generated photocurrent with a decrease of two orders of magnitude in the saturation current in devices from ESD films. Increases in Jsc are attributed to increased interfacial contact area between the TiO2 and PTEBS layers, while decreases in Voc are from poor film quality from ESD. Polymer solar cells (PSCs) with water-soluble active layers deposited by ESD were fabricated and tested. The water soluble, bulk heterojunction active layers consisted of PTEBS and the fullerene C60 pyrrolidine tris-acid. A single device structure of ITO/PEDOT:PSS/bulk(PTEBS+C60)/Al was used to study the effect of PTEBS to C60 tris-acid ratio on photovoltaic performance. An active layer ratio of PTEBS:C60 tris-acid (1:2) achieved the highest power conversion efficiency (0.0022%), fill factor (0.25), and open circuit voltage (0.56 V). The percolation threshold of C60 was achieved between 1 part PTEBS and 2 to 3 parts C60. Increasing the C60 tris-acid ratio (1:3) improved short circuit current, but reduced the open circuit voltage enough to lower efficiency

Semiconducting Electrospun Nanofibers for Energy Conversion

Nowadays, semiconducting thin films, thanks to their unique and excellent properties, play a crucial role for the design of devices for energy conversion and storage, such as solar cells, perovskite solar cells, lithium-ion batteries (LIBs), and fuel cells. Since the nanostructured arrangements can improve the behavior of the materials in several application fields, in this chapter we propose the electrospinning process as electro-hydrodynamic deposition to obtain semiconducting materials, in the form of nanofiber mats. The nanostructured mats are able to provide high surface-area-to-volume ratio and a microporous structure, which are crucial aspects for energetic application. In this chapter, we deeply describe the electrospinning process and how nanofibers obtained can be used in energy devices, satisfying all the requirements to improve overall final performances

Tailoring interfacial interactions in fiber reinforced polymeric composites by the electrospray deposition of waterborne carbon nanotubes

The utilization of fiber reinforced polymeric composites (FRPCs) has been broadening in recent years, especially in aerospace, automobile and marine industries, sports goods and many other high-performance applications, all of which demand enhanced thermal, electrical and mechanical properties. The ultimate performance of FRPCs can be enhanced by improving the fiber-matrix interface. Using nanophase reinforcements; tailoring fiber-matrix interface with carbon nanotubes (CNTs) or other carbon nanomaterials has shown significant improvements in properties of the composite. This thesis focuses on the deposition of CNTs onto carbon fabric (CF) surface by means of electrospray deposition and airbrush coating. Unlike the state-of-the-art methods to deposit carbon nanomaterials onto fiber surfaces, this study reports the deposition of CNTs from a waterborne dispersion, eliminates the use of organic volatile solvents and offers a method that is environmentally friendly and easily adaptable to large scale composite manufacturing processes. The hybrid CF-CNT structures prepared by surface deposition were used for the manufacturing of FPRCs by the vacuum infusion process (VIP) to assess the influence of CNTs on the stress transfer between the fiber-matrix interface. The surface morphology of the hybrid CNT-CF structures was characterized using scanning electron microscopy to verify homogeneous dispersion of CNTs on CF fabrics. CNTs deliberately placed at the fiber-matrix interface are expected to serve as stress transfer bridges between the fiber and the matrix and contribute to the enhancement of interlaminar shear strength and flexural properties. As by measured Mode I and Mode II interlaminar fracture testing experiment, CNT deposition on the CF surface strengthens the attachment of the laminate plie

Voltage-Controlled Deposition of Nanoparticles for Next Generation Electronic Materials

This work presents both a feasibility study and an investigation into the voltage-controlled spray deposition of different nanoparticles, namely, carbon nanotubes (CNTs), as well as molybdenum disulfide (MoS2) and tungsten disulfide (WS2) from the transition metal dichalcogenides (TMDCs) family of materials. The study considers five different types of substrates as per their potential application to next-generation device electronics. The substrates selected for this research were: 1) aluminum as a conducting substrate, 2) silicon as a semiconducting substrate, 3) glass, silicon dioxide (SiO2), and syndiotactic poly methyl methacrylate (syndiotactic PMMA) as insulating substrates. Since the 1990’s, carbon nanotubes have been the subject of intense research due to their extraordinary properties of conductivity, strength, and thermal stability. To utilize CNTs to their full potential, it is important to analyze their characteristics with respect to their amenability to deposition onto different substrate species, as future device technologies may demand. However, prior to the actual deposition, the natural tendency of CNTs to agglomerate must be taken into account. Thus, in this study the two commonly used methods of acid refluxing and surfactant treatment were used for dispersing the CNTs. Although CNTs were successfully dispersed in preparation for the form of voltage-controlled deposition developed for this research, a deeper investigation elucidated materials processing challenges stemming from the use of acid refluxing and surfactant-based methods. Thus, alternatively, a new method of dispersing CNTs, using isopropyl alcohol (IPA) and an anionic (positively charged) surfactant has been devised for this study. This, in conjunction with the five types of substrates, provided the testbed needed to investigate the feasibility of voltage-controlled spray deposition as a means for producing the uniform coatings of CNTs, the latter having application to device processing. On the other hand, TMDCs are garnering the attention of researchers due the extraordinary electronic, catalytic, and optical properties of these materials. The two particular TMDCs chosen for this work, MoS2 and WS2, are considered to be alternatives to, if not potential replacements for, the zero band gap conductor graphene. Both MoS2 and WS2 act as direct band gap semiconductors in single layer form and as indirect band gap semiconductors in multi-layer formation. This property makes these TMDCs promising as the basis for applications in solar cells, flexible electronics, sensors, and supercapacitors. However, systematic characterization and analysis are necessary to assess the suitability of any promising electronic material. Therefore, as with the aforementioned CNTs, in this study MoS2 and WS2 are dispersed in solvent, followed by deposition and characterization. Here again, the above-mentioned five different substrates are used as the template onto which these selected TMDCs are deposited via the method of voltage controlled spray deposition. The results of spectroscopic analysis, microstructural imaging, and characterization of the morphology of the nanoparticles and films deposited for this study will be presented. The effectiveness of the voltage-controlled spraying in light of these results will be discussed. Finally, a forward-looking study into the use of WS2 in surface enhanced Raman spectroscopy (SERS) has been undertaken in support of future work. This TMDC was used in conjunction with platinum to fabricate a WS2 based SERS substrate

Modification of Oxide Surfaces with Functional Organic Molecules, Nanoparticles, and Hetero-Oxide Layers

The research work described in this thesis is concerned with the modification of oxide surfaces, as reflected by its title. The surfaces and their modification have been studied using a range of experimental surface characterization tools, in particular x-ray photoelectron spectroscopy (XPS), fluorescence microscopy, scanning electron microscopy, atomic force microscopy, and scanning tunneling microscopy. A large part of the thesis is related to the modification of oxide or metal surfaces with nanoparticles. In particular, three different immobilization schemes for the coupling of molecularly imprinted polymer (MIP) nanoparticles to silicon oxide (SiO2) and gold surfaces were designed and characterized at every step. The first method reports the immobilization of MIPs using a photo-coupling agent in combination with an aminosilane compound. The second method explores an epoxysilane-based coupling agent to directly anchor the nucleophilic core-shell MIP nanoparticle to the surface. Both methods were proven to be non-destructive towards the specific binding sites of the MIP nanoparticles. The third scheme offers the immobilization of nucleophilic core-shell nanoparticles on model gold surfaces using self-assembled monolayers of 11-mercaptoundecanoic acid activated by carbodiimide/N-hydroxysuccinimide. All three coupling methods are quite versatile and can be used in biosensors to couple functional nano-objects with transducer surfaces. In addition to these investigation directly aimed at the immobilization of nanopartciles, more fundamentally oriented studies were carried out on the modification of the rutile TiO2(110) surface with silane molecules to obtain a detailed understanding of adsorption mechanism and geometry of these silanes. The deposition of a different type of nanopartciles, block copolymer reverse micelles loaded gold nanoparticles, on a titanium dioxide surface was tested using electrospray deposition. The study demonstrates that electrospray deposition is a viable method for depositing metal single-size metal nanoparticles onto a surface in vacuum, thereby retaining the clean vacuum conditions. Furthermore, it was shown that the removal of the block copolymer shell after deposition can be achieved both by atomic oxygen and an oxygen plasma, with the atomic oxygen being somewhat more efficient. Overall, it was demonstrated that a TiO2 surface decorated with narrow sized gold nanoparticles could be created, a result of importance in the catalysis domain. The last part of the thesis is concerned with the true in-situ investigation of growth of hetero-oxide layers on oxide surfaces from metal precursors. Tetraethyl orthosilicate (TEOS) was used as precursor for the chemical vapor deposition of silicon oxide on rutile TiO2(110). The growth was monitored in real time using ambient pressure XPS (APXPS), which revealed the dissociative adsorption with the formation of new species in the presence of a TEOS gas phase reservoir. Annealing results in the formation of SiO2 and of a mixed titanium/silicon oxide. Furthermore, tetrakis(dimethylamino)titanium was employed in the atomic layer deposition (ALD) of TiO2 on RuO2. The APXPS results showed evidence was for side reactions beyond the idealized scheme of ALD

Technologies for printing sensors and electronics over large flexible substrates: a review

Printing sensors and electronics over flexible substrates is an area of significant interest due to low-cost fabrication and possibility of obtaining multifunctional electronics over large areas. Over the years, a number of printing technologies have been developed to pattern a wide range of electronic materials on diverse substrates. As further expansion of printed technologies is expected in future for sensors and electronics, it is opportune to review the common features, complementarities and the challenges associated with various printing technologies. This paper presents a comprehensive review of various printing technologies, commonly used substrates and electronic materials. Various solution/dry printing and contact/non-contact printing technologies have been assessed on the basis of technological, materials and process related developments in the field. Critical challenges in various printing techniques and potential research directions have been highlighted. Possibilities of merging various printing methodologies have been explored to extend the lab developed standalone systems to high-speed roll-to-roll (R2R) production lines for system level integration

FABRICATION AND CHARACTERIZATION OF CONDUCTIVE MELT ELECTROSPUN FIBERS

Conductive polymer nanocomposites are a type of particle reinforced plastic composite where the doping material is electrically conductive. The diverse properties of an engineered composite material allow for the material properties to be fine-tuned for the specific application. This research focuses on using carbon allotropes, such as two-dimensional graphene and one-dimensional carbon nanotubes, to achieve direct current electrical conductivity through a polymer fiber. Melt electrospinning is the process used for creating the micrometer scale fibers by melting thermoplastic materials. High electrostatic fields apply a force to the polymer melt and a single fiber is drawn out. The resistivity of the bulk composite and composite fibers were characterized by four-point probe and van der Pauw resistivity measurements. Other material characterization methods such as X-ray diffraction and scanning electron microscopy were used to determine particle size and distribution in the polymer matrix. Several different polymers were used as the matrix material. Originally, the majority of the research focused on relatively low molecular weight varieties of polypropylene. Later, additional polymer samples of recycled polypropylene, polystyrene, and polyethylene terephthalate were supplied in collaboration with the Army Research Laboratory. Premade polypropylene and carbon nanotube composite material were supplied by Sandia National Laboratories and Virginia Tech. The graphene composites utilized polypropylene and polystyrene as the matrix material, and were made at Montana Tech. Recycled polyethylene terephthalate was used to create filament for rapid prototype machines