Download or read book Effects of Energetic Disorder on the Optoelectronic Properties of Organic Solar Cells written by Nikolaos Felekidis and published by Linköping University Electronic Press. This book was released on 2018-09-10 with total page 60 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPVs) is a promising low-cost and environmental-friendly technology currently achieving 12-14% power conversion efficiency. Despite the extensive focus of the research community over the last years, critical mechanisms defining the performance of OPVs are still topics of debate. While energetic disorder is known to be characteristic of organic semiconductors in general, its potential role in OPV has received surprisingly little attention. In this thesis we investigate some aspects of the relation between energetic disorder and several optoelectronic properties of OPV. Charge carrier mobility is a key parameter in characterizing the performance of organic semiconductors. Analyzing the temperature dependence of the mobility is also an oftenused method to obtain (estimates for) the energetic disorder in the HOMO and LUMO levels of an organic semiconductor material. Different formalisms to extract and analyze mobilities from space charge limited conductivity (SCLC) experiments are reviewed. Surprisingly, the Murgatroyd-Gill analytical model in combination with the Gaussian disorder model in the Boltzmann limit yields similar mobilities and energetic disorders as a more elaborate drift-diffusion model with parametrized mobility functionals. Common analysis and measurement errors are discussed. All the models are incorporated in an automated analysis freeware tool. The open circuit voltage (Voc) has attracted considerable interest as the large difference between Voc and the bandgap is the main loss mechanism in bulk heterojunction OPVs. Surprisingly, in ternary devices composed of two donors and one acceptor, the Voc is not pinned to the shallowest HOMO but demonstrates a continuous tunability between the binary extremities. We show that this phenomenon can be explained with an equilibrium model where Voc is defined as the splitting of the quasi-Fermi levels of the photo-created holes and electrons in a common density of states accounting for the stoichiometry, i.e. the ratio of the donor materials and the broadening by Gaussian disorder. Evaluating the PCE, it is found that ternary devices do not offer advantages over binary unless the fill factor (FF) is increased at intermediate compositions, as a result of improved transport/recombination upon material blending. Stressing the importance of material intermixing to improve the performance, we found that the presence of an acceptor may drastically alter the mobility and energetic disorder of the donor and vice versa. The effect of different acceptors was studied in a ternary onedonor- two-acceptors system, where the unpredictable variability with composition of the energetic disorder in the HOMO and the LUMO explained the almost linear tunability of Voc. Designing binary OPVs based on the design rule that the energetic disorder can be reduced upon material blending, as we observed, can yield a relative PCE improvement of at least 20%. CT states currently play a key role in evaluating the performance of OPVs and CTelectroluminescence (CT-EL) is assumed to stem from the recombination of thermalized electron-hole pairs. The varying width of the CT-EL peak for different material combinations is intuitively expected to reflect the energetic disorder of the effective HOMO and LUMO. We employ kinetic Monte Carlo (kMC) CT-EL simulations, using independently measured disorder parameters as input, to calculate the ground-to-ground state (0-0) transition spectrum. Including the vibronic broadening according to the Franck Condon principle, we reproduce the width and current dependence of the measured CT-EL peak for a large number of donor-acceptor combinations. The fitted dominant phonon modes compare well with the values measured using the spectral line narrowing technique. Importantly, the calculations show that CT-EL originates from a narrow, non-thermalized subset of all available CT states, which can be understood by considering the kinetic microscopic process with which electron-hole pairs meet and recombine. Despite electron-hole pairs being strongly bound in organic materials, the charge separation process following photo-excitation is found to be extremely efficient and independent of the excitation energy. However, at low photon energies where the charges are excited deep in the tail of the DOS, it is intuitively expected for the extraction yield to be quenched. Internal Quantum Efficiency (IQE) experiments for different material systems show both inefficient and efficient charge dissociation for excitation close to the CT energy. This finding is explained by kinetic Monte Carlo simulations accounting for a varying degree of e-h delocalization, where strongly bound localized CT pairs (< 2nm distance) are doomed to recombine at low excitation energies while extended delocalization over 3-5nm yields an increased and energy-independent IQE. Using a single material parameter set, the experimental CT electroluminescence and absorption spectra are reproduced by the same kMC model by accounting for the vibronic progression of the calculated 0-0 transition. In contrast to CT-EL, CT-absorption probes the complete CT manifold. Charge transport in organic solar cells is currently modelled as either an equilibrium or a non-equilibrium process. The former is described by drift-diffusion (DD) equations, which can be calculated quickly but assume local thermal equilibrium of the charge carriers with the lattice. The latter is described by kMC models, that are time-consuming but treat the charge carriers individually and can probe all relevant time and energy scales. A hybrid model that makes use of the multiple trap and release (MTR) concept in combination with the DD equations is shown to describe both steady-state space charge limited conductivity experiments and non-equilibrium time-resolved transport experiments using a single parameter set. For the investigated simulations, the DD-MTR model is in good agreement with kMC and ~10 times faster. Steady-state mobilities from DD equations have been argued to be exclusively relevant for operating OPVs while charge carrier thermalization and non-equilibrium time-dependent mobilities (although acknowledged) can be disregarded. This conclusion, based on transient photocurrent experiments with ?s time resolution, is not complete. We show that non-equilibrium kMC simulations can describe the extraction of charge carriers from subps to 100 ?s timescales with a single parameter set. The majority of the fast charge carriers, mostly non-thermalized electrons, are extracted at time scales below the resolution of the experiment. In other words, the experiment resolves only the slower fraction of the charges, predominantly holes.
Download or read book Optoelectronic Properties of Organic Semiconductors written by Nasim Zarrabi and published by Springer Nature. This book was released on 2022-02-26 with total page 116 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on organic semiconductors with particular attention paid to their use as photovoltaic devices. It addresses a fundamental and hitherto overlooked concept in the field of organic optoelectronics, namely the role that sub-gap states play in the performance of organic semiconducting devices. From a technological point of view, organic semiconductor-based devices are of significant interest due to their lightweight, ease of processability, conformal flexibility, and potentially low cost and low embodied energy production. Motivated by these rather unique selling points, the performance of organic semiconductors has been a subject of multidisciplinary study for more than 60 years with steady progress in applications such as solar cells, transistors, light emitting diodes, and various sensors. The book begins with a review of the main electro-optical phenomena in organic solar cells and presents a new method for measuring exciton diffusion lengths based on a low-quencher-content device structure. Furthermore, the book reveals how mid-gap trap states are a universal feature in organic semiconductor donor–acceptor blends, unexpectedly contributing to charge generation and recombination, and having profound impact on the thermodynamic limit of organic photovoltaic devices. Featuring cutting-edge experimental observations supported with robust and novel theoretical arguments, this book delivers important new insight as to the underlying dynamics of exciton generation and diffusion, charge transfer state dissociation, and indeed the ultimate fate of photogenerated free carriers.
Download or read book Elementary Processes in Organic Photovoltaics written by Karl Leo and published by Springer. This book was released on 2016-12-20 with total page 423 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume presents the results of a multi-year research programme funded by the Deutsche Forschungsgemeinschaft (German Research Council), which explains how organic solar cells work. In this new promising photovoltaic technology, carbon-based materials are deposited by low-cost methods onto flexible substrates, thus allowing devices which open completely new applications like transparent coatings for building, solar cells integrated into clothing or packages, and many more. The investigation of organic solar cells is an interdisciplinary topic, covering physics, chemistry and engineering. The different chapters address topics ranging from the synthesis of new organic materials, to the characterization of the elementary processes such as exciton transport and separation, and the principles of highly efficient device design. /div
Download or read book Smart Concepts for Mapping Optoelectronic Properties of Organic Solar Cells Strategies for Fast and Contactless Material Optimization written by Derya Baran and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Local Imaging of Optoelectronic Properties and Film Degradation in Polymer fullerene Solar Cells with Electrostatic Force Microscopy written by Phillip Alexander Cox and published by . This book was released on 2016 with total page 90 pages. Available in PDF, EPUB and Kindle. Book excerpt: With power conversion efficiencies on the rise, organic photovoltaics (OPVs) hold promise as a next-generation thin-film solar technology. However, both device performance and stability are inextricably linked to local film structure. Methods capable of probing nanoscale electronic properties as a function of film structure are thus a crucial component of the rational design of efficient and robust devices. This dissertation describes the use of three scanning probe methods for studying local charge generation and photodegradation in polymer/fullerene solar cells. First, we show that time-resolved electrostatic force microscopy (trEFM) is capable of resolving local photocurrent from sub-bandgap excitation down to attoampere level currents, a result unattainable by traditional contact-mode methods. We find that the local charging rates measured with trEFM are proportional to external quantum efficiency (EQE) measurements made on completed devices, making trEFM images equivalent to local EQE maps across the entire solar spectrum. For both phase-segregated and well-mixed MDMO-PPV:PCBM film morphologies, we show that the local distribution of photocurrent is invariant to excitation wavelength, providing local evidence for the controversial result that the probability of generating separated charge carriers does not depend on whether excitons are formed at the singlet state or charge transfer state. Next, we describe how local dissipation imaging can be performed with commercially-available frequency-modulated electrostatic force microscopy (FM-EFM) and show that dissipation maps are highly sensitive to photo-oxidative effects in organic semiconductors. We show that photo-oxidation induced changes in cantilever energy dissipation are proportional to device performance losses. We further develop dissipation imaging by implementing ringdown imaging, which directly measures the quality factor of the cantilever, enabling quantitative dissipation mapping. Using organic photovoltaic materials as a testbed, we study macroscopic device degradation as a function of photooxidation for three different film morphologies. According to EQE measurements, we find that the stability of the macroscopic devices is very sensitive to processing conditions, with films processed with the solvent additive 1,8-diiodooctane being the most stable. At the microscopic level, we compare the evolution of cantilever power dissipation as a function of photochemical degradation for three different polymer/fullerene blend morphologies, and show that the evolution of local power dissipation correlates with device stability. Lastly, we show that cantilever power dissipation increases more rapidly over large fullerene aggregates than in well-mixed polymer/fullerene regions, suggesting that local photochemistry on the fullerene contributes strongly to the dissipation signal.
Download or read book Organic Solar Cells written by Barry P. Rand and published by CRC Press. This book was released on 2014-08-26 with total page 812 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaic (OPV) cells have the potential to make a significant contribution to the increasing energy needs of the future. In this book, 15 chapters written by selected experts explore the required characteristics of components present in an OPV device, such as transparent electrodes, electron- and hole-conducting layers, as well as electron donor and acceptor materials. Design, preparation, and evaluation of these materials targeting highest performance are discussed. This includes contributions on modeling down to the molecular level to device-level electrical and optical testing and modeling, as well as layer morphology control and characterization. The integration of the different components in device architectures suitable for mass production is described. Finally, the technical feasibility and economic viability of large-scale manufacturing using fast inexpensive roll-to-roll deposition technologies is assessed.
Download or read book Encyclopedia of Polymer Applications 3 Volume Set written by Munmaya Mishra and published by CRC Press. This book was released on 2018-12-17 with total page 2954 pages. Available in PDF, EPUB and Kindle. Book excerpt: Undoubtedly the applications of polymers are rapidly evolving. Technology is continually changing and quickly advancing as polymers are needed to solve a variety of day-to-day challenges leading to improvements in quality of life. The Encyclopedia of Polymer Applications presents state-of-the-art research and development on the applications of polymers. This groundbreaking work provides important overviews to help stimulate further advancements in all areas of polymers. This comprehensive multi-volume reference includes articles contributed from a diverse and global team of renowned researchers. It offers a broad-based perspective on a multitude of topics in a variety of applications, as well as detailed research information, figures, tables, illustrations, and references. The encyclopedia provides introductions, classifications, properties, selection, types, technologies, shelf-life, recycling, testing and applications for each of the entries where applicable. It features critical content for both novices and experts including, engineers, scientists (polymer scientists, materials scientists, biomedical engineers, macromolecular chemists), researchers, and students, as well as interested readers in academia, industry, and research institutions.
Download or read book The Non Local Density of States of Electronic Excitations in Organic Semiconductors written by Carl. R Poelking and published by Springer. This book was released on 2017-10-24 with total page 133 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book focuses on the microscopic understanding of the function of organic semiconductors. By tracing the link between their morphological structure and electronic properties across multiple scales, it represents an important advance in this direction. Organic semiconductors are materials at the interface between hard and soft matter: they combine structural variability, processibility and mechanical flexibility with the ability to efficiently transport charge and energy. This unique set of properties makes them a promising class of materials for electronic devices, including organic solar cells and light-emitting diodes. Understanding their function at the microscopic scale – the goal of this work – is a prerequisite for the rational design and optimization of the underlying materials. Based on new multiscale simulation protocols, the book studies the complex interplay between molecular architecture, supramolecular organization and electronic structure in order to reveal why some materials perform well – and why others do not. In particular, by examining the long-range effects that interrelate microscopic states and mesoscopic structure in these materials, the book provides qualitative and quantitative insights into e.g. the charge-generation process, which also serve as a basis for new optimization strategies.
Download or read book Halide Perovskites written by Tze-Chien Sum and published by John Wiley & Sons. This book was released on 2019-03-25 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: Real insight from leading experts in the field into the causes of the unique photovoltaic performance of perovskite solar cells, describing the fundamentals of perovskite materials and device architectures. The authors cover materials research and development, device fabrication and engineering methodologies, as well as current knowledge extending beyond perovskite photovoltaics, such as the novel spin physics and multiferroic properties of this family of materials. Aimed at a better and clearer understanding of the latest developments in the hybrid perovskite field, this is a must-have for material scientists, chemists, physicists and engineers entering or already working in this booming field.
Download or read book The Physics of Solar Energy Conversion written by Juan Bisquert and published by CRC Press. This book was released on 2020-06-09 with total page 686 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research on advanced energy conversion devices such as solar cells has intensified in the last two decades. A broad landscape of candidate materials and devices were discovered and systematically studied for effective solar energy conversion and utilization. New concepts have emerged forming a rather powerful picture embracing the mechanisms and limitation to efficiencies of different types of devices. The Physics of Solar Energy Conversion introduces the main physico-chemical principles that govern the operation of energy devices for energy conversion and storage, with a detailed view of the principles of solar energy conversion using advanced materials. Key Features include: Highlights recent rapid advances with the discovery of perovskite solar cells and their development. Analyzes the properties of organic solar cells, lithium ion batteries, light emitting diodes and the semiconductor materials for hydrogen production by water splitting. Embraces concepts from nanostructured and highly disordered materials to lead halide perovskite solar cells Takes a broad perspective and comprehensively addresses the fundamentals so that the reader can apply these and assess future developments and technologies in the field. Introduces basic techniques and methods for understanding the materials and interfaces that compose operative energy devices such as solar cells and solar fuel converters.
Download or read book Electrical Processes in Organic Thin Film Devices written by Michael C. Petty and published by John Wiley & Sons. This book was released on 2022-01-24 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: Electrical Processes in Organic Thin Film Devices A one-stop examination of fundamental electrical behaviour in organic electronic device architectures In Electrical Processes in Organic Thin Film Devices: From Bulk Materials to Nanoscale Architectures, distinguished researcher Michael C. Petty delivers an in-depth treatment of the electrical behaviour of organic electronic devices focused on first principles. The author describes the fundamental electrical behaviour of various device architectures and offers an introduction to the physical processes that play a role in the electrical conductivity of organic materials. Beginning with band theory, the text moves on to address the effects of thin film device architectures and nanostructures. The book discusses the applications to devices currently in the marketplace, like displays, as well as those under development (transistors, solar cells, and memories). Electrical Processes in Organic Thin Film Devices also describes emerging organic thin film architectures and explores the potential for single molecule electronics and biologically inspired devices. Finally, the book also includes: A detailed introduction to electronic and vibrational states in organic solids, including classical band theory, disordered semiconductors, and lattice vibrations Comprehensive explorations of electrical conductivity, including electronic and ionic processes, carrier drift, diffusion, the Boltzmann Transport Equation, excess carriers, recombination, doping, and superconductivity An overview of important electro-active organic materials, like molecular crystals, charge-transfer complexes, conductive polymers, carbon nanotubes, and graphene Practical considerations of defects and nanoscale phenomena, including transport processes in low-dimensional systems, surfaces and interface states In-depth examinations of metal contacts, including ohmic contacts, the Schottky Barrier, and metal/molecule contacts A systematic guide to the operating principles of metal/insulator/semiconductor structures and the field effect A set of problems (with solutions on-line) for each chapter of the book Perfect for electronics developers and researchers in both industry and academia who study and work with molecular and nanoscale electronics, Electrical Processes in Organic Thin Film Devices also deserves a place in the libraries of undergraduate and postgraduate students in courses on molecular electronics, organic electronics, and plastic electronics.
Download or read book Photovoltaics Beyond Silicon written by Senthilarasu Sundaram and published by Elsevier. This book was released on 2024-06-28 with total page 819 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaics Beyond Silicon: Innovative Materials, Sustainable Processing Technologies, and Novel Device Structures presents the latest innovations in materials, processing and devices to produce electricity via advanced, sustainable photovoltaics technologies. The book provides an overview of the novel materials and device architectures that have been developed to optimize energy conversion efficiencies and minimize environmental impacts. Advances in technologies for harnessing solar energy are extensively discussed, with topics including materials processing, device fabrication, sustainability of materials and manufacturing, and the current state-of-the-art. Contributions from leading international experts discuss the applications, challenges and future prospects of research in this increasingly vital field, providing a valuable resource for students and researchers working in this area. Presents a comprehensive overview and detailed discussion of solar energy technology options for sustainable energy conversion Provides an understanding of the environmental challenges to be overcome and discusses the importance of efficient materials utilization for clean energy Looks at how to design materials processing and optimize device fabrication, including metrics such as power-to-weight ratio, effectiveness at EOL compared to BOL, life-cycle analysis
Download or read book Conjugated Polymers written by John R. Reynolds and published by CRC Press. This book was released on 2019-03-25 with total page 909 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers properties, processing, and applications of conducting polymers. It discusses properties and characterization, including photophysics and transport. It then moves to processing and morphology of conducting polymers, covering such topics as printing, thermal processing, morphology evolution, conducting polymer composites, thin films
Download or read book Design Strategies for Controlling Optoelectronic Properties and Solid State Order of Conjugated Materials in Organic Photovoltaics written by Olivia Pei-Hua Lee and published by . This book was released on 2013 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPVs) have emerged as an alternative technology to current silicon-based systems for harvesting solar energy. The solution-processability of conjugated materials offers the potential for scalable, low-cost production of lightweight, flexible solar cells. In particular, OPVs containing a bulk-heterojunction (BHJ) architecture, where electron-donors and electron-acceptors form an interpenetrating network within the device active layer, have demonstrated high solar cell performance. The active layer components serve a crucial role in light absorption, charge generation and carrier transport. Through synthetic design and device characterization, this work focuses on elucidating design strategies and principles for the development of high-performing electron-donors for OPVs. Molecular packing parameters of conjugated materials can strongly impact charge transport in the solid state. With a model polymer backbone containing thiophene comonomers, it was shown that strategic substitution of furan for thiophene improved material solubility and allowed for the use of linear alkyl side chains to reduce insulating contents in devices. These structural modifications yielded polymers with sufficient solubility, favorable solid-state morphology, enhanced long-range packing order, and efficient OPV performance. In a separate study, conjugated small molecules were functionalized with symmetric, planar end-groups so that they could self-assemble and form an interpenetrating network with electron-acceptors in the active layer. This investigation demonstrates that directing self-assembly via end-groups is an effective strategy to enhance molecular interconnectivity and improve the performance of molecular semiconductors in organic solar cells. Alongside solid-state morphology, semiconducting materials need to exhibit optical and electronic properties that enable effective light absorption and charge generation in solar cells. We showed that incorporating antiaromatic units into conjugated molecules effectively redshifted and broadened absorption to cover a significant portion of the visible spectrum. The impact of atomic substitution on optoelectronics was also explored with the design of an electron-poor monomer, oxadiazolopyridine, which yielded efficient OPV materials upon copolymerization with electron-donors. Furthermore, gold and silver nanoparticles were embedded in one of the device interlayers to enhance light absorption via surface plasmon resonance, improving OPV performance. Finally, influence of chemical structures on photoexcited charge transfer processes was investigated in a system containing organic electron-donors and inorganic electron-acceptor. Characterization by femtosecond-stimulated Raman spectroscopy provided information on electron transfer dynamics and molecular structural changes in the excited state. The results revealed that organic molecules containing trans-double bonds could isomerize into cis-double bonds upon photoexcitation, subsequently decreasing charge separation and device efficiency.
Download or read book Handbook of Organic Materials for Electronic and Photonic Devices written by Oksana Ostroverkhova and published by Woodhead Publishing. This book was released on 2018-11-30 with total page 911 pages. Available in PDF, EPUB and Kindle. Book excerpt: Handbook of Organic Materials for Electronic and Photonic Devices, Second Edition, provides an overview of the materials, mechanisms, characterization techniques, structure-property relationships, and most promising applications of organic materials. This new release includes new content on emerging organic materials, expanded content on the basic physics behind electronic properties, and new chapters on organic photonics. As advances in organic materials design, fabrication, and processing that enabled charge unprecedented carrier mobilities and power conversion efficiencies have made dramatic advances since the first edition, this latest release presents a necessary understanding of the underlying physics that enabled novel material design and improved organic device design. Provides a comprehensive overview of the materials, mechanisms, characterization techniques, and structure property relationships of organic electronic and photonic materials Reviews key applications, including organic solar cells, light-emitting diodes electrochemical cells, sensors, transistors, bioelectronics, and memory devices New content to reflect latest advances in our understanding of underlying physics to enable material design and device fabrication
Download or read book The Molecule Metal Interface written by Norbert Koch and published by John Wiley & Sons. This book was released on 2013-02-08 with total page 257 pages. Available in PDF, EPUB and Kindle. Book excerpt: Reviewing recent progress in the fundamental understanding of the molecule-metal interface, this useful addition to the literature focuses on experimental studies and introduces the latest analytical techniques as applied to this interface. The first part covers basic theory and initial principle studies, while the second part introduces readers to photoemission, STM, and synchrotron techniques to examine the atomic structure of the interfaces. The third part presents photoelectron spectroscopy, high-resolution UV photoelectron spectroscopy and electron spin resonance to study the electronic structure of the molecule-metal interface. In the closing chapter the editors discuss future perspectives. Written as a senior graduate or senior undergraduate textbook for students in physics, chemistry, materials science or engineering, the book's interdisciplinary approach makes it equally relevant for researchers working in the field of organic and molecular electronics.
Download or read book Organic Solar Cells written by Pankaj Kumar and published by CRC Press. This book was released on 2016-10-03 with total page 325 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book contains detailed information on the types, structure, fabrication, and characterization of organic solar cells (OSCs). It discusses processes to improve efficiencies and the prevention of degradation in OSCs. It compares the cost-effectiveness of OSCs to those based on crystalline silicon and discusses ways to make OSCs more economical. This book provides a practical guide for the fabrication, processing, and characterization of OSCs and paves the way for further development in OSC technology.
