Download or read book Molecular Engineering on Semiconducting Polymers for Enhancing Solar Cell Performance written by Wei-Hsuan Chang and published by . This book was released on 2016 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: A promising solution to address the present-day energy crisis is photovoltaic technology. Currently, the market is dominated by inorganic-based materials such as silicon, III-V semiconductors, CIGS, etc. Despite their technical maturity, the energy generated from these devices is still low. This is partially due to the high production cost of these materials. Therefore, the search for next generation photovoltaic technologies that utilize earth-abundant elements with low-cost production processes has been an intensive research area. Using solution-processable organic polymer semiconductors, polymer solar cells provide an opportunity to efficiently generate energy from sunlight at a reasonable cost. This is due to the ease of synthesis/modification of organic molecules and polymers compared to that of inorganic materials, the easily scalable solution-based fabrication process, and the use of cost-effective, environmentally friendly carbon-based elements. Owing to the vast research efforts over the past decade, the power conversion efficiencies of single- and multi-junction polymer solar cells have recently surpassed the 10% milestone. During this progression, materials development, driven by the desire to overcome the constraint of P3HT, has played a very important role in advancing the technology. To date, hundreds of photovoltaic polymers have been made through different combinations of conjugated building blocks and suitable functional groups. As a result, several state-of-the-art polymers, such as PTB7, PDPP3T, PBDTDPP and PffBT4T, have shown impressive performance. In order to keep this momentum going, further improvements and deeper insights into materials' property are certainly needed. In this dissertation, we particularly focus on improving the properties of several state-of-the-art photovoltaic polymers by resolving their shortcomings using innovative organic synthetic approaches. It is demonstrated that the materials' optoelectronic property as well as their fabrication process can be alternated through chemistry modification at a molecular scale, that is, by molecule engineering. This study paves a way not only to achieve high performance polymer solar cells, but also to provide novel synthetic strategies for researchers in the field to further push the boundaries of polymer solar cell technology in the future.
Download or read book Molecular Engineering of Polymer Semiconductors for Electronics and Photonics written by Ye-Jin Hwang and published by . This book was released on 2015 with total page 222 pages. Available in PDF, EPUB and Kindle. Book excerpt: There has been tremendous progress in the development of conjugated polymer semiconductors in the last two decades for diverse applications in organic electronics and photonics. Most notably, advances in p-type (hole-conducting) polymers have enabled the development of high-performance organic field-effect transistors (OFETs) as well as more efficient fullerene-based organic photovoltaics (OPVs). In contrast, n-type (electron-conducting) polymer semiconductors remain relatively scarce and consequently the performance of n-channel OFETs and all-polymer solar cells has lagged far behind p-channel OFETs and fullerene-based OPVs. This dissertation mainly focuses on the design and synthesis of new n-type polymer semiconductors for device applications in n-channel OFETs and non-fullerene OPVs. It aims to achieve better understanding of the relationships between molecular structure, processing, morphology, and device performance. New n-type polymer semiconductors were developed based on strong electron withdrawing naphthalene diimide (NDI) building block with various selenophene derivatives as co-monomers. The resulting highly crystalline poly(naphthalene diimide)s (PNDIs) gave the electron mobility as high as 0.24 cm2/Vs in n-channel OFET measurements in air which is comparable or even higher mobility compared to most of the p-channel transistors. Using NDI-selenophene copolymer, PNDIS-HD, as acceptor, a photovoltaic performance with a power conversion efficiency (PCE) of 3.3 % (Jsc = 7.78 mA/cm2, Voc = 0.76 V, FF = 0.55) was achieved in all-polymer solar cells, and this work has stimulated a lot of current interest in fullerene-free OPVs. In further studies in all-polymer solar cells, highly enhanced photovoltaic performance was achieved by chemical modifications of acceptor polymers and controlling self-organization kinetics of polymer/polymer blend films. From these studies, a critical role of the bulk crystallinity of acceptor polymer was revealed, and provided an important criterion for the molecular design of high performance polymer acceptors. Furthermore, all-polymer solar cells with more favorable bulk morphology by slow self-organization of polymers facilitated by room temperature film aging resulted in enhanced charge carrier mobility and photocurrent. Resulting all-polymer solar cells with PCE over 7 % showed a great potential of non-fullerene solar cells and demonstrated for the first time a viable alternative pathway to organic photovoltaics.
Download or read book Polymer Photovoltaics written by Fei Huang and published by Royal Society of Chemistry. This book was released on 2016 with total page 422 pages. Available in PDF, EPUB and Kindle. Book excerpt: An international perspective on the latest research in polymer solar cell technology.
Download or read book Semiconducting Polymers written by Georges Hadziioannou and published by John Wiley & Sons. This book was released on 2006-12-15 with total page 786 pages. Available in PDF, EPUB and Kindle. Book excerpt: The field of semiconducting polymers has attracted many researchers from a diversity of disciplines. Printed circuitry, flexible electronics and displays are already migrating from laboratory successes to commercial applications, but even now fundamental knowledge is deficient concerning some of the basic phenomena that so markedly influence a device's usefulness and competitiveness. This two-volume handbook describes the various approaches to doped and undoped semiconducting polymers taken with the aim to provide vital understanding of how to control the properties of these fascinating organic materials. Prominent researchers from the fields of synthetic chemistry, physical chemistry, engineering, computational chemistry, theoretical physics, and applied physics cover all aspects from compounds to devices. Since the first edition was published in 2000, significant findings and successes have been achieved in the field, and especially handheld electronic gadgets have become billion-dollar markets that promise a fertile application ground for flexible, lighter and disposable alternatives to classic silicon circuitry. The second edition brings readers up-to-date on cutting edge research in this field.
Download or read book Polymer Solar Cells Molecular Design and Microstructure Control written by Kui Zhao and published by Frontiers Media SA. This book was released on 2020-12-10 with total page 106 pages. Available in PDF, EPUB and Kindle. Book excerpt: This eBook is a collection of articles from a Frontiers Research Topic. Frontiers Research Topics are very popular trademarks of the Frontiers Journals Series: they are collections of at least ten articles, all centered on a particular subject. With their unique mix of varied contributions from Original Research to Review Articles, Frontiers Research Topics unify the most influential researchers, the latest key findings and historical advances in a hot research area! Find out more on how to host your own Frontiers Research Topic or contribute to one as an author by contacting the Frontiers Editorial Office: frontiersin.org/about/contact.
Download or read book Semiconducting Polymers written by Raquel Aparecida Domingues and published by CRC Press. This book was released on 2021-06-25 with total page 220 pages. Available in PDF, EPUB and Kindle. Book excerpt: Semiconducting polymers are of great interest for applications in electroluminescent devices, solar cells, batteries, and diodes. This volume provides a thorough introduction to the basic concepts of the photophysics of semiconducting polymers as well as a description of the principal polymerization methods for luminescent polymers. Divided into two main sections, the book first introduces the advances made in polymer synthesis and then goes on to focus on the photophysics aspects, also exploring how new advances in the area of controlled syntheses of semiconducting polymers are applied. An understanding of the photophysics process in this kind of material requires some knowledge of many different terms in this field, so a chapter on the basic concepts is included. The process that occurs in semiconducting polymers spans time scales that are unimaginably fast, sometimes less than a picosecond. To appreciate this extraordinary scale, it is necessary to learn a range of vocabularies and concepts that stretch from the basic concepts of photophysics to modern applications, such as electroluminescent devices, solar cells, batteries, and diodes. This book provides a starting point for a broadly based understanding of photophysics concepts applied in understanding semiconducting polymers, incorporating critical ideas from across the scientific spectrum.
Download or read book Polymers for Energy Storage and Conversion written by Vikas Mittal and published by John Wiley & Sons. This book was released on 2013-05-13 with total page 272 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the first comprehensive books to focus on the role of polymers in the burgeoning energy materials market Polymers are increasingly finding applications in the areas of energy storage and conversion. A number of recent advances in the control of the polymer molecular structure which allows the polymer properties to be more finely tuned have led to these advances and new applications. Polymers for Energy Storage and Conversion assimilates these advances in the form of a comprehensive text that includes the synthesis and properties of a large number of polymer systems for applications in areas such as lithium batteries, photovoltaics, and solar cells. Polymers for Energy Storage and Conversion: Introduces the structure and properties of polymer hydrogel with respect to its applications for low to intermediate temperature polymer electrolyte-based fuel cells Describes PVAc-based polymer blend electrolytes for lithium batteries Reviews lithium polymer batteries based on ionic liquids Proposes the concept of the solar cell with organic multiple quantum dots (MQDs) Discusses solvent effects in polymer-based organic photovoltaic devices Provides an overview of the properties of the polymers that factor into their use for solar power, whether for niche applications or for large-scale harvesting Reviews the use of macroporous organic polymers as promising materials for energy gas storage Readership Materials scientists working with energy materials, polymer engineers, chemists, and other scientists and engineers working with photovoltaics and batteries as well as in the solar and renewable energy sectors.
Download or read book High Efficiency Solar Cells written by Xiaodong Wang and published by Springer Science & Business Media. This book was released on 2013-11-01 with total page 664 pages. Available in PDF, EPUB and Kindle. Book excerpt: As part of the effort to increase the contribution of solar cells (photovoltaics) to our energy mix, this book addresses three main areas: making existing technology cheaper, promoting advanced technologies based on new architectural designs, and developing new materials to serve as light absorbers. Leading scientists throughout the world create a fundamental platform for knowledge sharing that combines the physics, materials, and device architectures of high-efficiency solar cells. While providing a comprehensive introduction to the field, the book highlights directions for further research, and is intended to stimulate readers’ interest in the development of novel materials and technologies for solar energy applications.
Download or read book Green solvent Processable Semiconducting Polymers Applicable in Additive free Perovskite and Polymer Solar Cells Molecular Weights Photovoltaic Performance and Thermal Stability1 written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Polymer Engineered Nanostructures for Advanced Energy Applications written by Zhiqun Lin and published by Springer. This book was released on 2017-06-16 with total page 717 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book provides a comprehensive overview of engineering nanostructures mediated by functional polymers in combination with optimal synthesis and processing techniques. The focus is on polymer-engineered nanostructures for advanced energy applications. It discusses a variety of polymers that function as precursors, templates, nano-reactors, surfactants, stabilizers, modifiers, dopants, and spacers for directing self-assembly, assisting organization, and templating growth of numerous diverse nanostructures. It also presents a wide range of polymer processing techniques that enable the efficient design and optimal fabrication of nanostructured polymers, inorganics, and organic–inorganic nanocomposites using in-situ hybridization and/or ex-situ recombination methodologies. Combining state-of-the-art knowledge from polymer-guided fabrication of advanced nanostructures and their unique properties, it especially highlights the new, cutting-edge breakthroughs, future horizons, and insights into such nanostructured materials in applications such as photovoltaics, fuel cells, thermoelectrics, piezoelectrics, ferroelectrics, batteries, supercapacitors, photocatalysis, and hydrogen generation and storage. It offers an instructive and approachable guide to polymer-engineered nanostructures for further development of advanced energy materials to meet ever-increasing global energy demands. Interdisciplinary and broad perspectives from internationally respected contributors ensure this book serves as a valuable reference source for scientists, students, and engineers working in polymer science, renewable energy materials, materials engineering, chemistry, physics, surface/interface science, and nanotechnology. It is also suitable as a textbook for universities, institutes, and industrial institutions.
Download or read book Morphology Control Strategies to Enable Printable Solar Cells written by Sebastian Alexander Schneider and published by . This book was released on 2021 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Rapidly decarbonizing our way of life, parti¬cularly the way we generate power, will be critical to mitigate the potentially catastrophic effects of climate change. Time is of the essence and low-cost and scaleable energy technologies that are equitable can play a key role in these efforts. Organic photovoltaics (OPVs) are an emerging technology based on semiconducting organic polymers and molecules with many potential benefits, such as low weight, flexibility, and printability. In recent years, the performance of research level OPVs has significantly increased, closing the gap to established silicon solar cell technologies. Arguably, printability is one of the key advantages of OPVs, as it can facilitate high-throughput production at extremely low cost. Yet, producing high efficiency OPVs with scaleable production methods such as roll-to-roll (R2R) printing is a key challenge that remains on the path to commercialization and implementation of OPVs. This is largely due to the fact that the efficiency of OPVs strongly depends on the complex microstructure -- also referred to as morphology -- of the active layer that converts light into electricity. Controlling the self-assembly of the materials during printing is significantly more challenging on the industrial scale than on the lab scale. In this thesis, three morphology control strategies are developed that enable direct transfer to scaleable printing techniques while maintaining high solar cell efficiencies. The focus of this work is on developing structure-performance relationships using a suite of synchrotron X-ray scattering techniques for in-depth morphological characterizations. Further, we use these techniques to study the self-assembly of the active layer in real-time during printing and provide mechanistic insight on how different morphology control strategies can be leveraged to optimize the morphology and thereby the performance of printed OPVs. First, a high-level introduction outlines the challenge of rapid decarbonization and the role emerging solar cell technologies such as OPVs can play in addressing this challenge. Special emphasis is placed on the challenge of scaleability on the path to commercialization of OPVs. Chapter 2 provides relevant theoretical background on the three key areas relevant to this thesis research. (I) Organic solar cells, (II) X-ray characterization techniques for organic thin films, and (III) scaleable printing techniques for organic solar cells. Chapter 3 describes a systematic side-chain engineering molecular design approach to control the self-aggregation of a widely used OPV acceptor polymer enabling high performance printable all-polymer solar cells. We find that a balanced propensity of donor and acceptor to self-aggregate is key to achieve intrinsic printability for this material system. Specifically, we show a simple yet effective way to modulate the self-aggregation of the commonly used naphthalene diimide (NDI)-based acceptor polymer (N2200) by systematically replacing a certain amount of alkyl side-chains with compact bulky side-chains (CBS) resulting in a series of random copolymer (PNDI-CBSx) with different molar fractions. Both solution-phase aggregation and solid-state crystallinity of these acceptor polymers are increasingly suppressed with increasing molar fractions of the CBS side-chain. We find that balanced aggregation strength between the donor and acceptor polymers is critical to achieve high-performance (up to 8.5% efficient) all-PSCs with optimal active layer film morphology. Further, we show that balanced aggregation strength of donor and acceptor yields an active layer morphology that is less sensitive to the film deposition methods and solution coating can be achieved without performance losses. Chapter 4 showcases the systematic fluorination of a PBDB-TFy donor and PNDI-TFx acceptor polymer (x, y = 0, 50, 75, 100) and discusses the impact active layer morphology and device performance. We find that fluorination of donor and acceptor polymers does not significantly alter the crystallinity of the respective neat polymers but results in increased compatibility -- in terms of reduced Flory-Huggins interaction parameter -- of the materials. We observe a systematic increase of device performance with increased extent of fluorination. Morphological studies reveal that this improvement largely stems from a more favorable blend morphology with reduced domain size. Specifically, we characterize the domain size of the best performing blend PBDB-TF100:PNDI-TF100 in detail with RSoXS and HRTEM techniques. We observe good agreement between both techniques yielding a domain size close to 30 nm representing a significantly reduce phase separation compare to the non-fluorinated control system PBDB-TF0:PNDI-TF0. Further, we explore the device optimization of this system with the commonly used DIO additive in detail and find that DIO selectively interacts with the donor polymer leading to increased face-on texture crystallinity, further improving the fill factor of the solar cells. Chapter 5 provides in-depth mechanistic insight into the in-situ morphology evolution of all-polymers solar cell systems during scaleable printing. We demonstrate how non-covalent interactions between donor and acceptor polymers can be leveraged to achieve a morphology evolution that is insensitive to changes in the drying conditions and that translates exceptionally well to printing fabrication. Specifically, we systematically control the donor-acceptor interactions using different extents of fluorination of PDBD-TFy and PNDI-TFx (x, y = 0, 0.5, 1.0) donor and acceptor polymers. We show that donor-acceptor interactions can induce donor crystallization, facilitating a high solar cell fill factor (0.65) and excellent transferability to printing fabrication. Leveraging this molecular design strategy, we fabricate printed devices with up to 6.82 % efficiency (compared to the 3.61 % efficient control system). Chapter 6 showcases a novel solvent additive approach based on phthalate additives to control polymer crystallinity and suppress unfavorable phase separation in a representative PTB7-Th/P(NDI2OD-2T) all-polymer solar cell. The best-performing additive increased the blade-coated device performance from 2.09 to 4.50% power conversion efficiency, an over two-fold improvement, mitigating the loss in performance that is typically observed during process transfer from spin-coating to blade-coating. We find that the improved device performance stems from a finer polymer phase-separation size and overall improved active layer morphology. Real-time X-ray diffraction measurements during blade-coating provide mechanistic insights and suggest that the dioctyl phthalate additive may act as a compatibilizer, reducing the demixing of the donor and acceptor polymer during film formation, enabling a smaller phase separation and improved performance. Chapter 7 concludes this thesis with a summary of key conclusions and future directions of this work. Specifically, mixed phase characterization and morphology evolution of polymer:NFA systems, potential morphology control strategies for state-of-the-art all-polymer solar cells, and solvent quality and temperature aggregation studies are briefly discussed. Lastly, the appendix to this thesis provides an overview of selected examples of structural characterization of functional organic thin films to develop structure-property relations in organic solar cells and adjacent field such as organic field effect transistors (OFETs).
Download or read book Rational Design of Solar Cells for Efficient Solar Energy Conversion written by Alagarsamy Pandikumar and published by John Wiley & Sons. This book was released on 2018-08-31 with total page 400 pages. Available in PDF, EPUB and Kindle. Book excerpt: An interdisciplinary guide to the newest solar cell technology for efficient renewable energy Rational Design of Solar Cells for Efficient Solar Energy Conversion explores the development of the most recent solar technology and materials used to manufacture solar cells in order to achieve higher solar energy conversion efficiency. The text offers an interdisciplinary approach and combines information on dye-sensitized solar cells, organic solar cells, polymer solar cells, perovskite solar cells, and quantum dot solar cells. The text contains contributions from noted experts in the fields of chemistry, physics, materials science, and engineering. The authors review the development of components such as photoanodes, sensitizers, electrolytes, and photocathodes for high performance dye-sensitized solar cells. In addition, the text puts the focus on the design of material assemblies to achieve higher solar energy conversion. This important resource: Offers a comprehensive review of recent developments in solar cell technology Includes information on a variety of solar cell materials and devices, focusing on dye-sensitized solar cells Contains a thorough approach beginning with the fundamental material characterization and concluding with real-world device application. Presents content from researchers in multiple fields of study such as physicists, engineers, and material scientists Written for researchers, scientists, and engineers in university and industry laboratories, Rational Design of Solar Cells for Efficient Solar Energy Conversion offers a comprehensive review of the newest developments and applications of solar cells with contributions from a range of experts in various disciplines.
Download or read book Molecular and Nanoscale Engineering of High Efficiency Excitonic Solar Cells written by and published by . This book was released on 2016 with total page 20 pages. Available in PDF, EPUB and Kindle. Book excerpt: We combined the synthesis of new polymers and organic-inorganic hybrid materials with new experimental characterization tools to investigate bulk heterojunction (BHJ) polymer solar cells and hybrid organic-inorganic solar cells during the 2007-2010 period (phase I) of this project. We showed that the bulk morphology of polymer/fullerene blend solar cells could be controlled by using either self-assembled polymer semiconductor nanowires or diblock poly(3-alkylthiophenes) as the light-absorbing and hole transport component. We developed new characterization tools in-house, including photoinduced absorption (PIA) spectroscopy, time-resolved electrostatic force microscopy (TR-EFM) and conductive and photoconductive atomic force microscopy (c-AFM and pc-AFM), and used them to investigate charge transfer and recombination dynamics in polymer/fullerene BHJ solar cells, hybrid polymer-nanocrystal (PbSe) devices, and dye-sensitized solar cells (DSSCs); we thus showed in detail how the bulk photovoltaic properties are connected to the nanoscale structure of the BHJ polymer solar cells. We created various oxide semiconductor (ZnO, TiO2) nanostructures by solution processing routes, including hierarchical aggregates and nanorods/nanotubes, and showed that the nanostructured photoanodes resulted in substantially enhanced light-harvesting and charge transport, leading to enhanced power conversion efficiency of dye-sensitized solar cells.
Download or read book Functional Supramolecular Nanoassemblies of Conjugated Molecules written by Penglei Chen and published by Frontiers Media SA. This book was released on 2020-01-13 with total page 159 pages. Available in PDF, EPUB and Kindle. Book excerpt: Π-conjugated systems of delocalized aromatic electrons along their backbones, including conjugated small molecules, oligomers, polymers, and carbonaceous materials, etc., have received considerable attention from a wide variety of scientific and technical communities. Compared to inorganic materials, the advantages of those based on π-tectons lie in their broad diversity, flexibility, and tunability with regard to structure/geometry/morphology, processability, composition, functionality, electronic/band structure, etc. In terms of sophisticated molecular engineering, these features endow them not only with excellent self-assembly properties but also with unique optical, electrical, mechanical, photophysical, photochemical, and biochemical attributes. This renders them promising scaffolds for advanced functional materials (AFMs) in numerous areas of general interest such as electronics, optics, optoelectronics, photovoltaics, magnetic and piezoelectric devices, sensors, catalysts, biomedicines, and others. With regard to the design/synthesis of novel π-tectons, the launch of diverse assembly/fabrication protocols, theoretical calculations, etc., the past several decades have witnessed tremendous advancements along this direction. Thus far, a vast array of high-performance π-tectons-based AFMs have been initiated. To some extent, the cooperative principle of π-πstacking and other noncovalent interactions has been revealed, and the structure-property relationships have been disclosed. Despite the existing progress, this field still faces challenges, for example: (i) the need for scalable assembly/manufacture under ambient conditions—with low-cost, facile, environmentally-friendly protocols (ii) clearer correlations bridging the underlying intricate relationships of each successive step in assembly/manufacture (iii) corresponding theoretical calculations for guiding the rational design of π-tectons that elucidate the cooperative principle of π-π stacking and other noncovalent interactions, as well as the principle of structure-performance correlation (iv) stability and durability, among the most important concerns regarding their commercialization The advancements accumulated during the past decades have established a solid foundation for the further development of π-conjugated systems-based AFMs. We believe that with unrelenting efforts from both scientific and technical communities of various backgrounds, their practical applications will eventually be fulfilled. This Research Topic aims to address the above-mentioned challenges
Download or read book Encyclopedia of Renewable Energy Sustainability and the Environment written by and published by Elsevier. This book was released on 2024-08-09 with total page 4061 pages. Available in PDF, EPUB and Kindle. Book excerpt: Encyclopedia of Renewable Energy, Sustainability and the Environment, Four Volume Set comprehensively covers all renewable energy resources, including wind, solar, hydro, biomass, geothermal energy, and nuclear power, to name a few. In addition to covering the breadth of renewable energy resources at a fundamental level, this encyclopedia delves into the utilization and ideal applications of each resource and assesses them from environmental, economic, and policy standpoints. This book will serve as an ideal introduction to any renewable energy source for students, while also allowing them to learn about a topic in more depth and explore related topics, all in a single resource.Instructors, researchers, and industry professionals will also benefit from this comprehensive reference. - Covers all renewable energy technologies in one comprehensive resource - Details renewable energies' processes, from production to utilization in a single encyclopedia - Organizes topics into concise, consistently formatted chapters, perfect for readers who are new to the field - Assesses economic challenges faced to implement each type of renewable energy - Addresses the challenges of replacing fossil fuels with renewables and covers the environmental impacts of each renewable energy
Download or read book Solution Processable Organic Semiconducting Materials for Thin Film Transistors and Photovoltaic Applications written by Sang-wŏn Ko and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic transistors and solar cells offer the potential advantages of low-cost, large-scale fabrication by solution processing techniques, and compatibility with both flexible and lightweight plastic substrates. Continuous development of new organic materials has improved their performance, thus enabling the commercialization of these conducting polymers in recent years. However, understanding the relationship between polymer packing structures and mobilities is still lacking. Furthermore, to enable a polymer to serve as an effective donor material in bulk heterojunction (BHJ) solar cells, several important properties have to be considered, such as band gap, absorption coefficient, effective charge transport, and a relatively deep HOMO. Needless to say, careful balancing of these properties remains challenging. Thus, this thesis aims to gain a better understanding of materials design rules to address the above issues using two types of conjugated polymers. First, new donor-acceptor copolymers were designed and synthesized to gain insights into designing efficient donor materials in BHJ solar cells. Second, poly(3,4-disubstituted thiophene) derivatives were designed and synthesized to study relationships between structural design, packing, charge transport property, and solar cell performance. In the first part of my thesis, I have prepared vinylene linked co-polymers in order to achieve low bandgap polymers by extending [Pi]-conjugation lengths. I found that the hole mobilities of the polymers scaled with the molecular weights in these amorphous polymers. Optical absorption at longer wavelengths was improved by eliminating torsions along the polymer backbones. Current density (Jsc) in BHJ solar cells depended on the overall intensity of absorption and hole mobility of donor materials. Comparing to the amorphous vinylene linked co-polymers, charge carrier mobility could be enhanced by employing thienopyrazine based co-polymers, which contain rigid fused aromatic rings promoting well ordered inter-chain packing. Removing of the adjacent thiophene groups around the thienopyrazine acceptor core markedly increased the optical absorption of the polymer and raised its ionization potential, resulting in power conversion efficiency (PCE) of 1.57%. This investigation on the new co-polymers could provide a useful guideline for designing efficient donors for BHJ solar cells. In the second part of my thesis, I designed and synthesized polythiophene derivatives to understand structure-property relationships in detail. Despite their slightly larger band gaps, polythiophene derivatives are nonetheless important active materials due to their high absorption coefficients and high charge transport mobilities. Furthermore, their facile synthesis and ease of structural modifications with various substituents are the advantages of using polythiophene derivatives as model conjugated polymer systems. To examine the influence of backbone twisting on performance of transistors and BHJ solar cells, I systematically imposed twists within the conjugated backbones of poly(3,4-disubtituted thiophene (P34AT) using a unsubstituted thiophene spacer of varying sizes. When a moderate twist was introduced to the P34AT backbone, a 19% enhancement in the open-circuit voltage vs. poly(3-hexylthiopene) based devices and high PCE (4.2%) were achieved without sacrificing the short-circuit current density and the fill factor. Despite the high charge transport mobility (0.17 cm2/Vs), P34AT hardly showed [Pi]-[Pi] stacking in X-ray diffraction, suggesting that a strong [Pi]-[Pi] stacking is not always necessary for high charge carrier mobility; in which other potential polymer packing motifs (in addition to the edge-on structure) can lead to a high device performance. To gain further knowledge in structure-property relationships of the less explored 3,4-disubstituted polythiophene system, various P34AT derivatives were prepared and their opto-electronic property, packing structure, and device performance were studied. Among P34AT derivatives containing fused thiophene rings, a higher PCE was achieved with a benzodithiophene based polymer (PDHBDT) having a larger absorption coefficient, higher hole mobility, and deeper HOMO. The PDHBDT also exhibited a thermotropic phase transition behavior, leading to mobility up to 0.46 cm2/Vs where the polymer backbones adapt an edge-on lamellar packing structure. In the last part of this thesis, low band gap P34AT derivatives, which incorporate electron withdrawing groups, were prepared to improve photocurrent. However, I observed that a low absorption coefficient and a low hole mobility limited current density in solar cells. Thus, this indicates that low band gap polymers with strong absorption properties and good charge transports are critical towards molecular design for achieving high PCE. Collectively, through rational design and characterization of these novel polymers, this thesis has illustrated that better understanding of molecular design rules for engineering opto-electronic properties and packing behavior, will lead to higher device performance.
Download or read book Molecular Devices for Solar Energy Conversion and Storage written by Haining Tian and published by Springer. This book was released on 2017-09-14 with total page 539 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book shows the different molecular devices used for solar energy conversion and storage and the important characterization techniques for this kind of device. It has five chapters describing representative molecule-based solar cells, such as organic solar cells, dye-sensitized solar cells and hybrid solar cells (perovskite solar cell and quantum dots solar cells). It also includes two chapters demonstrating the use of molecular devices in the areas of solar fuel, water splitting and carbon dioxide reduction. There are further two chapters with interesting examples of solar energy storage related devices, like solar flow battery, solar capacitor and solar energy-thermal energy storage. Three chapters introduce important techniques used to characterize, investigate and evaluate the mechanism of molecular devices. The final chapter discusses the stability of perovskite solar cells. This book is relevant for a wide readership, and is particularly useful for students, researchers and industrial professionals who are working on molecular devices for solar energy utilization.
