Download or read book Nano Sc Ale Investigation of Structural and Electrical Properties of Self Organized Thin Films of Phthalocyanines A Progress Towards New Photovoltaic Material written by and published by . This book was released on 2008 with total page 536 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ongoing efforts to improve the efficiency of organic photovoltaic cells emphasize the significance of the architecture of molecular assemblies in thin films, at nanometer and micron length scales, to enhance both exciton diffusion and charge transport, in donor and acceptor layers. Controlled growth of molecules via self-assembly techniques presents new opportunities to develop nano-structured organic thin films for electronic devices. This thesis is focused on controlling the orientation of phthalocyanine molecular assemblies in thin films in order to demonstrate the impact of microscopic control of molecular order on electrical properties and organic solar cell device performance. The studies performed here provide insights into the self-assembling behavior, film morphology, nanoscale electrical conductivity, and photovoltaic properties of a disk-shaped peripherally substituted phthalocyanine (Pc) molecule possessing amide functional groups in the side chains. Amide functionality was integrated in the side chains of this phthalocyanine molecule with the purpose of increasing the intra-columnar interaction through formation of a hydrogen bonding network between molecules, and to guide columnar orientation in a preferred direction via specific surface-molecule interactions. It is realized that molecule-substrate interactions must dominate over molecule-molecule interactions to achieve control over the deposition of molecules in a preferred direction for organic solar cell applications. Microscopic imaging and spectroscopic studies confirm the formation of flat-lying, well ordered, layered phthalocyanine films as anticipated. The remarkable electrical conductivity of the flat-lying phthalocyanine molecules, as studied by Conducting tip Atomic Force Microscopy (C-AFM) provide the impetus for the formation of organic solar cells based on layers of these hydrogen bonding phthalocyanine molecules. The photocurrent from devices that are made with the ordered Pc molecules and disordered Pc molecules as the primary photoactive donor layer, and vacuum deposited C60 as the acceptor material, were evaluated. The results presented here demonstrate the feasibility of increasing the photogenerated current by controlling the molecular organization in the photo active layer.

Download or read book Dissertation Abstracts International written by and published by . This book was released on 2009 with total page 810 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Recent Advances in Thin Films written by Sushil Kumar and published by Springer Nature. This book was released on 2020-08-27 with total page 721 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume comprises the expert contributions from the invited speakers at the 17th International Conference on Thin Films (ICTF 2017), held at CSIR-NPL, New Delhi, India. Thin film research has become increasingly important over the last few decades owing to the applications in latest technologies and devices. The book focuses on current advances in thin film deposition processes and characterization including thin film measurements. The chapters cover different types of thin films like metal, dielectric, organic and inorganic, and their diverse applications across transistors, resistors, capacitors, memory elements for computers, optical filters and mirrors, sensors, solar cells, LED's, transparent conducting coatings for liquid crystal display, printed circuit board, and automobile headlamp covers. This book can be a useful reference for students, researchers as well as industry professionals by providing an up-to-date knowledge on thin films and coatings.

Download or read book Structural Characterization of Photovoltaic Nanocrystals Single Crystals and Thin Film Semiconductors written by Erin Elizabeth Jedlicka and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: According to the U.S. Energy Information Administration, solar and wind make up over two-thirds of the 39.7 giga-watts (GW) of new energy capacity added to the grid in 2021. In addition, wind turbine service technicians and solar panel installers are ranked number one and number three respectively on the U.S. Bureau of Labors "Fastest Growing Occupations for 2019-2029". However, currently solar panels require energy-consuming manufacturing processes, are limited to inflexible substrates, and only convert around 20-30% of light into electricity. Many new alternative materials for solar cells emerged with in the past few decades with low-cost solution processing, the ability to print onto flexible substrates, and the potential to convert higher percentages of light into electricity. However, most studies focus on the improvements in performance without studying the impact that changing processing conditions and adding dopants has on the vertical composition and crystalline structure of the material. Here, we study the structural characteristics of different photovoltaic materials to determine the impact of different processing methods and dopants. First, we investigate the vertical composition in solution processed photovoltaic semiconductor materials. While solution-processed solar cells offer a low-cost and less energy consuming manufacturing method, the processing materials and method highly impact the performance of the solar cell. In Chapter 2, we investigate how changes in processing photovoltaic thin-films impacts the film morphology and vertical composition of the film. We use glow discharge optical emission spectroscopy (GDOES) coupled with scanning electron microscopy (SEM) to analyze changes in film morphology. We look at three types of semiconductor materials: polymer/quantum dot blends, kesterite, and chalcopyrite. In polymer/quantum dot blends use GDOES to confirm the depth composition from a three-dimensional reconstruction using discrete algebraic reconstruction technique (DART) from scanning electron microscopy images. We discover that a post-deposition ligand exchange directly from the native quantum dot ligands to shorter, electrically conducting ligands results in damage to film causing cracks and voids. However, using a solution-based exchange to an intermediary ligand before a post-deposition ligand prevents damage to the film and results in better device performance. Next, we use GDOES to show that Ag-doping in kesterite films results in a more homogenous composition throughout the film depth and reduces the voids in the film. Finally, we discover that the selenization copper-rich under higher pressure allows results in films with fewer voids and Na-passivated defects. Overall, we see that processing conditions impact the vertical composition and can change the performance of photovoltaic materials. In addition to changes from processing conditions, changes in material properties can be induced by doping the material. In Chapter 3, we investigate how doping changes the structure of methylammonium lead tribromide (MAPbBr3) single crystals. We observe a shift in the structural phase transition temperature as a result of bismuth incorporation into the crystal structure. Using x-ray diffraction, we discover a contraction in the lattice constant with increase bismuth concentration. We compare the lattice contraction to the effects of applying external pressure to MAPbBr3 and observe a similar shift to lower temperatures for the phase transition. We use density functional theory (DFT) simulations and determine the likely defect species to be BiPb+. In our final chapter, we investigate the impacts of a remote outreach activity on student knowledge and attitudes towards science. We use pre/post-activity surveys to evaluate changes in student understanding of Next Generation Science Standards (NGSS) aligned content about the relationship between energy production and the environment. We also use 5-point Likert-scale surveys to measure student attitudes towards STEM/STEM careers. We use quantitative statistical analysis methods such as Welch’s t-test, Mann-Whitney U test, and Wilcoxon Signed Ranked test to determine the significance of changes between pre/post-activity surveys. We find an increase in the probability of students identifying wind, hydropower, and nuclear energy as renewable resources on the post-survey. Similarly, for non-renewable resources we find an increase in the probability that students identify fossil fuels, gas, and nuclear on the post-activity survey. We observe no changes in student attitudes towards STEM/STEM careers between pre/post survey. However, we determine that teachers over-estimated the changes in student attitudes from the outreach activity. We also observe an interesting result in the post-activity surveys with a higher mean response for “I enjoyed this [outreach] activity” and compared to the mean response for “I enjoy science and engineering activities”. This discrepancy in student attitudes should be further studied, however this provides insight in how we can improve student attitudes towards science and engineering activities.

Download or read book Nanoscale investigation of the mechanical and electrical properties of polyaniline graphene oxide Composite thin films fabricated by physical mixture method written by 龍友翰 and published by . This book was released on 2020 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book A New Nanostructured Multinary Compounds Thin Film For Photovoltaics written by Fiat Varol Songul and published by LAP Lambert Academic Publishing. This book was released on 2015-07-23 with total page 64 pages. Available in PDF, EPUB and Kindle. Book excerpt: A multinary chalcopyrite compound CuInGaSeTe has been investigated and characterized as absorber layer for thin film solar cell material in this work. This work is a collaboration of multidisciplinary departments such as physics, materials science and energy systems science.The basic principles of a photovoltaic device are introduced and then material characteristics have been evaluated as structural, optical, topographical, electrical and also surface properties have been discussed. Special emphasis is laid on the complex fabrication process and its characteristic parameters for applications as PV material.

Download or read book Novel Materials Computational Spectroscopy and Multiscale Simulation in Nanoscale Photovoltaics written by Marco Bernardi (Ph. D.) and published by . This book was released on 2013 with total page 104 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaic (PV) solar cells convert solar energy to electricity using combinations of semiconducting sunlight absorbers and metallic materials as electrical contacts. Novel nanoscale materials introduce new paradigms for ultrathin, lightweight, solution processable PV as an alternative to conventional Si technology. For example, the ability to use deposition methods not viable in conventional inorganic PV is particularly exciting as products like paper, textiles, automobiles, and building materials could be coated with PV devices, thus making solar cells ubiquitous. In addition, the optical absorption, band gap, and charge carrier mobility of nanoscale materials can be tuned by tailoring their chemistry or using quantum confinement effects, thus creating novel opportunities for efficient and inexpensive solar cells. From the viewpoint of the fundamental processes involved in PV operation, nanoscale PV poses additional challenges due to the formation of strongly bound electron-hole pairs (excitons) upon photoabsorption requiring the presence of semiconductor heterointerfaces within the active layer to dissociate excitons and generate charge carriers. Such interfaces are known as donor-acceptor (D-A) interfaces, and their presence leads to correlated exciton and charge dynamics in nanoscale PV. Material combinations suitable for nanoscale PV can be predicted using atomistic quantum mechanical calculations, which further enable the computation of a small number of spectroscopic quantities necessary to estimate the power conversion efficiency. Our work shows the computational design of two novel classes of materials for nanoscale PV displaying optical absorption, stability, tunability, and carrier mobility superior to materials employed so far in nanoscale PV. To this end, we employed simulation techniques generally falling under the umbrella of ab initio atomistic electronic structure methods, including density functional theory (DFT) and the GW-Bethe-Salpeter approach. Proof-of-concept PV devices were fabricated and tested within our group and in collaboration with other experimental research groups. The two material families studied in this thesis include carbon based materials (both in nanoscale and bulk form) and two-dimensional monolayers such as graphene, reduced graphene oxide, boron nitride, and transition metal dichalcogenides. Our work demonstrates the feasibility of novel PV devices with a range of benefits employing such materials. It further develops a framework to accurately predict exciton dissociation at D-A interfaces and estimate efficiencies in nanoscale PV. Beyond our work on nanoscale materials, we introduce a combination of methods to enable simulation of nanoscale PV across time and length scales. We discuss modeling of subpicosecond dynamics at D-A interfaces, device-scale transport of excitons, charge carriers, and photons, and macroscopic sunlight management by arranging solar panels to best couple with the Sun's trajectory. We elaborate on the latter point and discuss our work on simulation and fabrication of macroscopic three-dimensional PV structures with promise to deliver a range of benefits for solar energy conversion, including reduced seasonal and latitude sensitivity and a doubling of peak power generation hours. Taken together, this thesis advances the computational design of nanoscale PV systems and introduces novel families of materials and PV structures with technological promise for next-generation PV. This thesis document is organized as follows: Chapter 1 and Chapter 2 introduce, respectively, nanoscale PV and ab initio atomistic simulation methods employed in this work. Chapter 3 is the core of our work on novel families of materials for nanoscale PV, and Chapter 4 illustrates multi-scale simulation methods in nanoscale PV as well as our work on three-dimensional PV. The key results are briefly summarized in Chapter 5.

Download or read book Advances in Thin Films Nanostructured Materials and Coatings written by Alexander D. Pogrebnjak and published by Springer. This book was released on 2019-02-09 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights the latest advances in chemical and physical methods for thin-film deposition and surface engineering, including ion- and plasma-assisted processes, focusing on explaining the synthesis/processing–structure–properties relationship for a variety of thin-film systems. It covers topics such as advances in thin-film synthesis; new thin-film materials: diamond-like films, granular alloys, high-entropy alloys, oxynitrides, and intermetallic compounds; ultra-hard, wear- and oxidation-resistant and multifunctional coatings; superconducting, magnetic, semiconducting, and dielectric films; electrochemical and electroless depositions; thin-film characterization and instrumentation; and industrial applications.

Download or read book Relating Nanoscale Structure to Electronic Function in Organic Semiconductors Using Time resolved Spectroscopy written by Christopher Grieco and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Molecular packing arrangements at the nanoscale level significantly contribute to the ultimate photophysical properties of organic semiconducting materials used in solar energy conversion applications. Understanding their precise structure-function relationships will provide insights that can lead to chemical and structural design rules for the next generation of organic solar cell materials. In this work, two major classes of materials were investigated: Singlet fission sensitizers and semiconducting block-copolymers. By exploiting chemical design and film processing techniques, a variety of controllable nanoscale structures could be developed and related to their subsequent photophysical properties, including triplet and charge transport. Time-resolved optical spectroscopies, including both absorption and emission techniques, were used to measure the population dynamics of excited states and charge carriers following photoexcitation of the semiconducting materials. Singlet fission, an exciton multiplication reaction that promises to boost solar cell efficiency by overcoming thermalization loss, has been characterized in several organic molecules. If the energetics are such that the excited state singlet energy is at least twice the triplet energy, then a singlet exciton may split into two triplet excitons through an intermolecular energy-sharing process. The thin film structure of a model singlet fission compound was exploited by modulating its crystallinity and controlling polymorphism. A combination of visible, near-infrared, and mid-infrared transient absorption spectroscopies were used to investigate the precise singlet fission reaction mechanism. It was determined that the reaction intermediates consist of bound triplet pairs that must physically separate in order to complete the reaction, which results in multiplied, independent triplet excitations. Triplet transfer, which is modulated by molecular packing arrangements that control orbital overlap coupling, was found to determine the efficacy of triplet pair separation. Furthermore, the formation of these independent triplets was found to occur on longer (picosecond) timescales than previously believed, indicating that any kinetically competing relaxation processes, such as internal conversion, need to be controlled. Last, it was found that the diffusion of the multiplied triplet excitons, and thus their harvestability in devices, is highly influenced by the crystallinity of the material. In particular, the presence of even a small amount of contaminant amorphous phase was determined to be detrimental to the ultimate triplet diffusion length. Future research directions are outlined, which will be used to develop further chemical and structural design rules for the next generation of singlet fission chromophores. Semiconducting block-copolymers, because of their natural tendency to self-assemble into ordered nanoscale structures, offer an appealing strategy for controlling phase segregation between the hole and electron transport materials in organic solar cells. Such phase segregation is important for both ensuring efficient conversion of the photogenerated excitons into charge carriers, and for creating percolation pathways for efficient transport of the charges to the device electrodes. Time-resolved mid-infrared spectroscopy was developed for monitoring charge recombination kinetics in a series of block-copolymer and polymer blend films possessing distinct, controlled nanoscale morphologies. In addition to explaining previous work that correlated film structure to device efficiency, it was revealed how the covalent linkage in block-copolymers can be carefully designed to prevent rapid recombination losses. Furthermore, novel solution-phase systems of block-copolymer aggregates and nanoparticles were developed for future fundamental spectroscopic work. Future studies promise to explain precisely how polymer chain organization, including intrachain and interchain interactions, governs their ultimate charge photogeneration and transport properties in solar cells.

Download or read book Materials Growth and Optoelectronic Properties of Nano needle Structured Sn rich SnO Thin Films written by Andrew A. Wong and published by . This book was released on 2014 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt: The rising global interest in photovoltaics and consumer electronics has heightened the demand for earth-abundant optoelectronic materials. Transparent conductive oxides (TCOs) in particular have been widely studied due to their unique material properties and versatility in a variety of applications. However, many of the common TCO materials suffer tradeoffs between cost, environmental stability, and fabrication requirements in addition to their optical and electronic properties. Tin monoxide (SnO) has become an intriguing TCO candidate due to its p-type conductivity, unique among oxide semiconductors. Yet prior studies show these materials require delicate preparation conditions and result in modest electrical and optical performance. In this study, we report a novel method of preparing Sn-rich SnO thin films using a comproportionation reaction of Sn and SnO2. These thin films are fabricated through magnetron co-sputtering of Sn and SnO2 and then undergo crystallization through thermal annealing at different temperatures and in varied ambient environments. Material properties are quantified through techniques such as X-ray diffraction, scanning electron microscopy, energy dispersive spectroscopy, electron backscatter diffraction, spectrophotometry (with integrating sphere), 4-point probe, hot probe and Hall effect measurements. This thesis reports the rapid (15-60 seconds), low temperature (210-300 °C) crystallization of these thin films to form SnO nano-needles with embedded Sn plasmonic scatters. Sn-rich SnO thin films can be laser pre-patterned to establish nucleation centers and control nano-needle size. These nanoscale features are advantageous for light-trapping in low temperature photovoltaic technologies such as a-Si or CIGS. Furthermore, parallel experimental-theoretical studies suggest that Sn-rich SnO thin films on thin film Ge could have 2-5x absorption increase the near infrared regime. This would be ideal for thermophotovoltaic and infrared-photodetector applications. We also report very high electrical conductivity (1560 S/cm), carrier concentrations (~1021 cm−3), and the highest reported p-type mobility (~100-1850 cm2/V/s) of any metal oxide thin film. The observation of strong p+ conductivity is highly unusual for oxide semiconductors. Furthermore we observe oxygen ambient-controlled ambipolar behavior in these thin films, another rare oxide feature. These findings present unique additions to scientific understanding of TCO materials and open opportunities for future experimental and theoretical research.

Download or read book New Directions in Thin Film Nanophotonics written by Sreekanth K. V. and published by . This book was released on 2019 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights recent advances in thin-film photonics, particularly as building blocks of metamaterials and metasurfaces. Recent advances in nanophotonics has demonstrated remarkable control over the electromagnetic field by tailoring the optical properties of materials at the subwavelength scale which results in the emergence of metamaterials and metasurfaces. However, most of the proposed platforms require intense lithography which makes them of minor practical relevance. Stacked ultrathin-films of dielectrics, semi-conductors, and metals are introduced as an alternative platform that perform unique or similar functionalities. This book discusses the new era of thin film photonics and its potential applications in perfect and selective light absorption, structural coloring, biosensing, enhanced spontaneous emission, reconfigurable photonic devices and super lensing.

Download or read book Advances in Thin Films Nanostructured Materials and Coatings written by Alexander D. Pogrebnjak and published by . This book was released on 2019 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This book highlights the latest advances in chemical and physical methods for thin-film deposition and surface engineering, including ion- and plasma-assisted processes, focusing on explaining the synthesis/processing–structure–properties relationship for a variety of thin-film systems. It covers topics such as advances in thin-film synthesis; new thin-film materials: diamond-like films, granular alloys, high-entropy alloys, oxynitrides, and intermetallic compounds; ultra-hard, wear- and oxidation-resistant and multifunctional coatings; superconducting, magnetic, semiconducting, and dielectric films; electrochemical and electroless depositions; thin-film characterization and instrumentation; and industrial applications.

Download or read book Metallophthalocyanine Thin Films written by Corneliu Nicolai Colesniuc and published by . This book was released on 2011 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic semiconductors represent a class of carbon-based compounds with a tremendous potential to exhibit novel physical properties, and to be used in new and important applications. They display different properties compared to their inorganic counterparts, and present many advantages such as unlimited potential to be synthesized in new molecular structures, and capability of being processed inexpensively. Metallophthalocyanines (MPc) belong to the small-molecule group of organic semiconductors, and represent a model system for the whole class of flat, organic molecules. This dissertation presents a study of the structure and the electrical and magnetic properties of thin phthalocyanine films and phthalocyanine-based devices. Chapter one gives an introduction to the general properties of organic semiconductors and the wide range of their physical properties. In particular, the metallophtalocyanines are introduced as being a model system for the small-molecule group of organic semiconductors. Metallophthalocyanines are very well suited to be grown in thin films using organic molecular beam deposition (OMBD) techniques. Chapter two discusses the fabrication of thin phthalocyanine films and devices using OMBD, and the study of their structural properties using a wide range of experimental methods. The molecular shape anisotropy, combined with the interplay between intermolecular and the molecule-substrate interactions, determine different thin film structures that can be controlled by the fabrication conditions. The structure of phthalocyanine thin films determines their electrical transport properties. Chapter three investigates the electrical transport properties of hybrid metal-organic sandwich devices. These properties are controlled not only by the organic film, but also by the metal-organic interfaces. It was found that the low-voltage regime is linear, i.e. Ohmic, for a wide range of temperatures and organic layer thicknesses. The conductance increases exponentially with the temperature and decreases exponentially with the thickness. This behavior was explained with a model that incorporates tunneling between localized states with thermally-induced overlap. Chapter 4 studies the magnetic properties of MPcs. They are controlled by the central metal ion, and the type of molecular stacking in thin films, and were studied using DC magnetometry and magneto-optical techniques. Experimental data suggest the existence of two different magnetic regimes as a function of temperature.

Download or read book Correlating Nanoscale Optoelectronic and Mechanical Properties of Solution Processable Thin Film Photovoltaic Materials Using Scanning Probe Microscopy written by Sarah M. Vorpahl and published by . This book was released on 2017 with total page 150 pages. Available in PDF, EPUB and Kindle. Book excerpt: Solution processable materials present a competitive alternative to traditional silicon solar cells based on inexpensive processing and flexible form factors. Several competing technologies have entered the market in the past few years, including cadmium telluride and copper, indium, gallium, sulfur (CIGS) alloys. In addition to this nascent commercialized product, several emerging technologies also offer promising alternatives. Copper, zinc, tin, sulfur (CZTS) kesterite materials offers an earth abundant option, moving away from more price volatile minerals such as the indium used in CIGS. Hybrid perovskites (HPs) have been revealed as one of the most exciting new solution processable materials, with efficiency improving exponentially in just the past several years. This dissertation explores the underlying electrical and mechanical properties of both CZTS and HP thin films using scanning probe microscopy (SPM). Using several correlated SPM techniques, local functional properties are related to bulk performance as a way to help understand the fundamental properties that drive material characteristics.

Download or read book Nanostructured Photovoltaic Devices for Next Generation Solar Cell written by Sung Jin Kim and published by . This book was released on 2008 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: As the search for alternative sources of energy other than petroleum continues to expand, solar energy conversion has already been identified as one of the most promising technologies. In the past few years there has been extensive research focused on the next generation solar cells that can exceed the Shockley-Queisser limit (a model that predicts the maximum achievable efficiency for a given material with a given bandgap). Moreover, nanoengineering approaches to enhance solar power conversion efficiency have started to receive considerable interest. Even in the most efficient commercially available solar devices utilizing crystalline silicon, a major portion of the absorbed ultraviolet photon energy is wasted as heat. Furthermore, this heat is detrimental to device reliability. Colloidal nanocrystal quantum dots (NQDs) offer the exciting prospect of simultaneously manipulating device and material structures and processes to enable more efficient solar energy conversion. Most importantly, these colloidal nanocrystal quantum dots are amenable to inexpensive fabrication techniques such as dip coating or spray coating of the constituent nanoscale materials onto various substrates. This dissertation focuses on the development of nanostructured photovoltaic devices, that exhibit multiple exciton generation, and that exploit the wide absorption spectra enabled by the quantum dots for next generation highly efficient, low cost, solar cells. Firstly, multiple exciton generation and subsequent electrical extraction from a thin film photoconductive device constructed from PbSe NQDs is demonstrated. As an extension of this work, this PbSe NQD photoconductor was used in a tandem structure with a polymer solar cell to demonstrate multiple carrier extraction the application of an external electric field. This structure exhibited improved device durability from UV irradiation due to the self-passivating effect provided by the PbSe layer. In order to achieve better exciton dissociation and charge transport, novel NQDs with functionalized ligands were developed. This research included the development of an approach to produce predefined patterns of quantum dots and multipod nanocrystals. The technique used optical lithography for direct writing of device structures for optoelectronic and electronic devices as well as the ability to change the ligand properties by using heat treatment. CdSe, CdTe, and PbSe nanocrystals were all functionalized by the incorporation of the functional ligand t -butoxycarbonyl (t -BOC). The ability to modify ligands of spin-casted nanocrystal layers by heating enables the fabrication of multi-layered structures. Moreover, the direct photopatterning of nanocrystal device structures was facilitated by the incorporation of a photo acid generator with the t -BOC functionalized nanocrystals. Finally, three different approaches that were recently developed to use t -BOC protected NQDs for photovoltaic devices will be discussed. The three types of devices that were developed include: (1) a multi-layered NQD all inorganic heterojunction photovoltaic devices; (2) a Schottky junction solar cell using a metal electrode on a NQD thin film; and (3) a hybrid (NQD/Polymer) bulk heterojunction device. Detailed characterization of these devices demonstrated that the t -BOC protected NQDs can be used to boost device performance (as compared to devices made from NQD with other ligands). This result provides significant advantages for realizing complicated device structures in the future.

Download or read book Nanoscale Properties of Low Dimensional Crystalline Organic Semiconductor Films written by Alexander Buyanin and published by . This book was released on 2016 with total page 98 pages. Available in PDF, EPUB and Kindle. Book excerpt: The self-assembly and optoelectronic properties of model crystalline organic semiconductor films was studied by atomic force microscopy (AFM) techniques. Small molecule organic semiconductors serve as model systems for the active materials in organic electronic devices. Applications such as organic solar cells and light-emitting diodes rely on organic polymers and small molecules for their properties but the performance of these organic devices could still yet be improved compared to the inorganic-based devices. The aim of this work is to study different structure-property relationships in model organic systems to gain a better understanding for designing organic electronic material. Other spectroscopic and structural techniques are used to complement the spatial mapping capability of AFM, providing a more comprehensive view of the fundamental processes governing organic semiconductor films. First, self-assembled oligothiophenes with different surface functionalization are studied for the role humidity has on the electronic properties of a monolayer film. In-situ AFM and x-ray photoelectron spectroscopy (XPS) show that the water vapor is found to change the electronic properties of films with hydrophilic surface termination groups leaving hydrophobic films unaffected. Next, different indigo small molecules are self-assembled at the air-water interface into crystalline structures. The role of intermolecular interactions is found to play a critical role in the indigo crystal morphology. The self-assembled indigo crystals are studied by photoluminescence (PL) spectroscopy revealing the presence of H-aggregate formation during self-assembly. Further studies of the electronic properties of the indigo crystal films are performed using electrical AFM techniques and field-effect transistors. Finally, a scheme for the fabrication of flat field-effect transistors using graphene photolithography is presented. Graphene field-effect transistors are fabricated and tested providing a platform to study more accurately thin organic semiconducting films. This dissertation demonstrates the advantage of studying model systems of organic semiconductors with nanoscale precision with the aim of designing better performing organic electronic devices.

Download or read book Novel Nanostructured Thin Film Heterostructures Growth Nanoscale Characterization and Properties written by and published by . This book was released on 2004 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: During my graduate study, I have been involved in the growth of new nano heterostructures grown by Pulsed Laser Deposition and by Laser MBE with the emphasis on understanding the thin film growth process by a new paradigm of Domain Matching Epitaxy (DME) and to integrate them on substrates like silicon, sapphire and new metallic substrates like Ni RaBiTS with exciting technological applications. The DME involves matching of integral multiples of lattice planes (diffracting as well as nondiffracting) between the film and the substrate, and this matching could be different in different directions. The idea of matching planes is derived from the basic fact that during thin film growth lattice relaxation involves generation of dislocations whose Burgers vectors correspond to missing or extra planes, rather than lattice constants. In the DME framework, the conventional lattice matching epitaxy (LME) becomes a special case where matching of lattice constants results from matching of lattice planes with a relatively small misfit of less than 7-8%. In large lattice mismatch systems, epitaxial growth of thin films is possible by matching of domains where integral multiples of lattice planes match across the interface. The work done in my doctoral study is divided into two main segments, a) Growth of layered nanostructures and b) growth of nanostructured composite thin films. The three systems studied under the first segment are 1) Growth of epitaxial self-aligned insulating films on metals (Cu) and its integration with Si (100). 2) Growth and integration of LSMO with Si (100). 3) Growth of Si on Ni substrates (highly textured) with TiN as a buffer layer. The heterostructures studied under the second part are 1) Role of Self-assembled Gold Nanodots in Improving the Electrical and Optical Characteristics of Zinc Oxide Films and 2) Growth of high quality epitaxial ZnO-Pt Nanocomposite and ZnO/Pt, Nanolayer Structures on Sapphire (0001). The epitaxial growth of these heterostruc.