Download or read book Effect of Morphology on Molecular Organic Solar Cells written by Stefan Grob and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book How Molecular Morphology Affects the Performance of Organic Solar Cells written by Jonathan Alan Bartelt and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic bulk heterojunction (BHJ) solar cells consisting of electron-donating polymers and electron-accepting fullerene derivatives garner interest because they can be manufactured inexpensively at high throughput via solution processing. The power conversion efficiency of BHJ solar cells is now above 11 and 12% in single-junction and tandem architectures, respectively. Much of the recent improvement in device performance is due to (i) the development of low band gap polymers with broad absorption capabilities, (ii) the development of polymers and fullerene derivatives with energy levels optimized for higher open-circuit voltages, and (iii) the use of solvent additives to tailor the BHJ morphology. Despite these improvements, the efficiency of single junction BHJ solar cells must surpass 15% before organic solar cells can compete with inorganic solar cells based on silicon or cadmium telluride. In this doctoral thesis, I examine how the polymer and fullerene morphology affect the performance of BHJ solar cells and determine how the efficiency of these devices can be improved. In Chapter 2, I show that the morphology of polymer-fullerene BHJs consists of three phases: pure polymer aggregates, pure fullerene clusters, and an amorphous phase consisting of polymer and fullerene mixed at the molecular level. The concentration of fullerene in the molecularly mixed phase has a strong influence on device performance. In order to have a fully percolated network of electron transporting fullerene molecules within the mixed regions, at least 20 weight percent fullerene must be mixed with the polymer. Decreasing the concentration of fullerene below this percolation threshold reduces the number of electron transport pathways within the mixed regions and creates morphological electron traps that enhance charge-carrier recombination and decrease device efficiency. In Chapter 3, I discuss how the polymer molecular weight plays a role in determining the final BHJ morphology and device efficiency. BHJs made with low molecular weight polymer have exceedingly large fullerene-rich domains. Increasing the molecular weight of the polymer decreases the size of these domains and significantly improves device efficiency. I show that polymer aggregation in solution affects the size of the fullerene-rich domains and determine that this effect is linked to the dependency of polymer solubility on molecular weight. Due to its poor solubility, high molecular weight polymer quickly aggregates in solution and forms a network that acts as a template and prevents large scale phase separation. Finally, I find that the performance of devices made with low molecular weight polymer can be improved by using solvent additives during processing to force the polymer to aggregate in solution. I examine how the efficiency of organic solar cells can be improved to 15% in Chapter 4. To surpass 15% efficiency, devices likely will need to be 300 nm thick and achieve fill factors near 0.8. Using a numerical device simulator, I show that the key to achieving these performance metrics is a high charge-carrier mobility and a low recombination rate constant. Devices with low charge-carrier mobility (10-2 cm2 V-1 s-1) suffer from high rates of bimolecular recombination because many charge carriers must reside in the device to drive a given drift current. Furthermore, I demonstrate that numerical device simulators are a powerful tool for investigating charge-carrier transport in BHJ devices and are useful for rapidly prototyping BHJ solar cells. To conclude, I discuss how researchers can improve the efficiency of organic solar cells. Researchers should aim to design molecular systems that exhibit high miscibility ( 20 weight percent fullerene in the mixed phase) or immiscibility (H" weight percent fullerene in the mixed phase). Furthermore, the synthesis of new, high molecular weight polymers with exceptionally high charge-carrier mobility and low recombination rate constants is imperative for reaching high device fill factor. With these improvements, the efficiency of organic solar cells can surpass 15%, which would allow these devices to compete with traditional inorganic solar cell technologies.

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 Understanding the Impact of Molecular Reorganization on Morphology Formation and Charge Transfer in Organic Solar Cells written by Stefan Wedler and published by . This book was released on 2021 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Correlating structure and function in small molecule organic solar cells by means of scanning probe and electron microscopy written by Michael Scherer and published by BoD – Books on Demand. This book was released on 2016-07-20 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this work nanoscale properties in active layers of small molecule organic solar cells are studied regarding their impact on device performance. For this, the effect of variations in stack design and process conditions is examined both electrically and with high resolution imaging techniques. Two topics are addressed: (i) the visualization of charge extraction/injection properties of solar cell contacts and (ii) the tailoring of structural properties of co-evaporated material blends for bulk heterojunction (BHJ) organic solar cells. (i) We study the impact of controlled contact manipulation on the internal electric potential distribution of fluorinated zincphtalocyanine (F4ZnPc)/fullerene (C60) organic solar cells under operating conditions. In a detailed analytical study using photoelectron spectroscopy and in-operando scanning Kelvin probe microscopy it is demonstrated that the electric field distribution of organic solar cells at the maximum power point depends in an overproportional manner on contact properties and ranges from bulk to contact dominated even for solar cells with decent device performance. (ii) The morphology of co-evaporated active layer blends depends on both substrate and substrate temperature. Here we study the morphology of F4ZnPc:C60 blends with analytical transmission electron microscopy. For all substrates used is found that co-evaporation of the materials at elevated substrate temperature (100° Cel) induces a distinct phase segregation of F4ZnPc and C60. However, only when using a C60 underlayer, as in inverted devices, also the crystallinity of the segregated C60 phase increases. There is only a slight increase in crystallinity when F4ZnPc acts as an underlayer, as typically for non-inverted devices. Solar cell characterization reveals that the crystalline C60 domains are the main driving force for enhanced free charge carrier generation and higher power conversion efficiencies. With this we could provide a novel explanation why record efficiencies of small molecule organic solar cells are realized in inverted device architecture only.

Download or read book The Influence of Morphology and Molecular Orientation on the Efficiency and Lifetime of Organic Solar Cells written by Sibi Sutty and published by . This book was released on 2015 with total page 148 pages. Available in PDF, EPUB and Kindle. Book excerpt: One of the reasons for the low efficiency of organic solar cells (OSCs) is because the relationship between morphology and molecular orientation of the organic semiconductors and the performance and lifetime of the OSC is not well understood. Theoretically, the morphology and molecular orientation of organic semiconductors influence the three major processes that determine the performance of an OSC. These processes are i) light absorption, ii) exciton dissociation and iii) charge transport. The general objective of this research work is to understand how the morphology of the active layers in an OSC affects these three processes with the aim of gaining insights that can be used to improve OSC efficiency and lifetime. The relationship between device physics and morphology is studied by analyzing the photovoltaic performance, external quantum efficiency, UV/visible absorption, charge conductivity and surface morphology of the fabricated OSCs and relevant organic semiconductor active layers. Chapters 5 and 6 in this work study the impact of varying the donor-acceptor ratio in OSCs. The best OSC performance was found to occur at high fullerene concentrations due to increased fullerene aggregation resulting in larger absorption and exciton dissociation in the OSC. Building on this insight, OSCs comprising a mixed layer with high fullerene content followed by a neat fullerene layer, was identified to possess the highest performance of all other device architectures due to balanced charge generation and charge collection. Chapters 7 and 8 in this work study the impact of varying the molecular orientation of phthalocyanine donor materials using templating layers on the performance and lifetime of planar heterojunction OSCs. Templating layers force the phthalocyanine molecules to lie flat on the substrate affecting the three main OSC processes. Depending on the combination of the templating layer and phthalocyanine, different aspects of the OSC device physics are altered leading to large differences in performance gains obtained from templating. Finally, it was found that the morphology of the donor material affects the morphology of fullerene acceptor deposited on top, which results in substantial variation in the lifetimes of phthalocyanine/fullerene planar heterojunction OSCs.

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 Organic Solar Cells written by Ingmar Bruder and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Organic and Hybrid Solar Cells written by Hui Huang and published by Springer. This book was released on 2014-11-25 with total page 342 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book delivers a comprehensive evaluation of organic and hybrid solar cells and identifies their fundamental principles and numerous applications. Great attention is given to the charge transport mechanism, donor and acceptor materials, interfacial materials, alternative electrodes, device engineering and physics, and device stability. The authors provide an industrial perspective on the future of photovoltaic technologies.

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 338 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.

Download or read book Stability and Degradation of Organic and Polymer Solar Cells written by Frederik C. Krebs and published by John Wiley & Sons. This book was released on 2012-04-23 with total page 375 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPV) are a new generation of solar cells with the potential to offer very short energy pay back times, mechanical flexibility and significantly lower production costs compared to traditional crystalline photovoltaic systems. A weakness of OPV is their comparative instability during operation and this is a critical area of research towards the successful development and commercialization of these 3rd generation solar cells. Covering both small molecule and polymer solar cells, Stability and Degradation of Organic and Polymer Solar Cells summarizes the state of the art understanding of stability and provides a detailed analysis of the mechanisms by which degradation occurs. Following an introductory chapter which compares different photovoltaic technologies, the book focuses on OPV degradation, discussing the origin and characterization of the instability and describing measures for extending the duration of operation. Topics covered include: *Chemical and physical probes for studying degradation *Imaging techniques *Photochemical stability of OPV materials *Degradation mechanisms *Testing methods *Barrier technology and applications Stability and Degradation of Organic and Polymer Solar Cells is an essential reference source for researchers in academia and industry, engineers and manufacturers working on OPV design, development and implementation.

Download or read book Small Molecule Semiconductors for High Efficiency Organic Solar Cells written by Chuanlang Zhan and published by Frontiers Media SA. This book was released on 2019-08-15 with total page 184 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Effects of Molecular Structure and Processing on Morphology and Performance of Small Molecule Solar Cells written by John A. Love and published by . This book was released on 2015 with total page 202 pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation is concerned with the materials properties of conjugated molecules and their application in bulk heterojunction (BHJ) type solar cells with particular attention paid to the role of processing in determining morphology and device performance. Utilizing alternating electron rich and electron deficient moieties in the conjugated backbone results in tunable energy levels allowing molecules to be tailored to achieve desired optoelectronic characteristics. Two high performance materials in particular are studied in detail with respect to their physical and electronic properties. Specifically, high-resolution transmission electron microscopy, atomic force microscopy, UV-viable absorption spectroscopy and x-ray diffraction are used to examine the BHJ nanostructure in conjunction with current voltage measurements to elucidate structure property relationships. A series of molecules designed for specific goals such as improved absorption and electronics are also each briefly described. Though none of these materials give high efficiencies in BHJ solar cells compared with the first two materials, these smaller studies help demonstrate the intricacies of controlling morphology and how it can affect device performance.

Download or read book High Performance Organic Solar Cells written by Huawei Hu and published by . This book was released on 2017 with total page 143 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Phthalocyanines written by Leznoff, C. C. (Clifford C.) and published by New York : VCH, 1989-c1996.. This book was released on 1989 with total page 328 pages. Available in PDF, EPUB and Kindle. Book excerpt: Up-to-date and written by leading experts, this book is unique in a rapidly expanding field. It provides in-depth discussions and descriptions of the materials, electronic properties and applications of phthalocyanines. Aspects of phthalocyanines covered include * synthesis * polymer aspects * electronic spectroscopy * excited state chemistry and physics * chemical sensors * biological aspects (e.g. photodynamic therapy of cancer) The numerous tables, chemical structures, and references are particularly handy source materials for both the novice and experienced researcher and industrial practitioner interested in phthalocyanines.

Download or read book Organic Solar Cells written by Wolfgang Tress and published by Springer. This book was released on 2014-11-22 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers in a textbook-like fashion the basics or organic solar cells, addressing the limits of photovoltaic energy conversion and giving a well-illustrated introduction to molecular electronics with focus on the working principle and characterization of organic solar cells. Further chapters based on the author’s dissertation focus on the electrical processes in organic solar cells by presenting a detailed drift-diffusion approach to describe exciton separation and charge-carrier transport and extraction. The results, although elaborated on small-molecule solar cells and with focus on the zinc phthalocyanine: C60 material system, are of general nature. They propose and demonstrate experimental approaches for getting a deeper understanding of the dominating processes in amorphous thin-film based solar cells in general. The main focus is on the interpretation of the current-voltage characteristics (J-V curve). This very standard measurement technique for a solar cell reflects the electrical processes in the device. Comparing experimental to simulation data, the author discusses the reasons for S-Shaped J-V curves, the role of charge carrier mobilities and energy barriers at interfaces, the dominating recombination mechanisms, the charge carrier generation profile, and other efficiency-limiting processes in organic solar cells. The book concludes with an illustrative guideline on how to identify reasons for changes in the J-V curve. This book is a suitable introduction for students in engineering, physics, material science, and chemistry starting in the field of organic or hybrid thin-film photovoltaics. It is just as valuable for professionals and experimentalists who analyze solar cell devices.

Download or read book Role of Molecular Architecture and Interface Morphology on the Performance of Organic Solar Cells written by and published by . This book was released on 2005 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: