Design Strategies for Controlling Optoelectronic Properties and Solid-State Order of Conjugated Materials in Organic Photovoltaics PDF Download

Author: Olivia Pei-Hua Lee
Publisher:
ISBN:
Category :
Languages : en
Pages : 174

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Book Description
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.

Author: Christoph Brabec
Publisher: John Wiley & Sons
ISBN: 3527623205
Category : Technology & Engineering
Languages : en
Pages : 597

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Book Description
Providing complementary viewpoints from academia as well as technology companies, this book covers the three most important aspects of successful device design: materials, device physics, and manufacturing technologies. It also offers an insight into commercialization concerns, such as packaging technologies, system integration, reel-to-reel large scale manufacturing issues and production costs. With an introduction by Nobel Laureate Alan Heeger.

Author: Changhe Guo
Publisher:
ISBN:
Category :
Languages : en
Pages :

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Book Description
State-of-the-art organic photovoltaics rely on kinetically trapped, partially phase-separated structures of donor/acceptor mixtures to create a high interfacial area for exciton dissociation and networks of bicontinuous phases for charge transport. Nevertheless, intrinsic structural disorder and weak intermolecular interactions in polymer blends limit the performance and stability of organic electronic devices. We demonstrate a potential strategy to control morphology and donor/acceptor heterojunctions through conjugated block copolymer poly(3-hexylthiophene)-block-poly((9,9-dioctylfluorene)-2,7-diyl-alt-[4,7-bis(thiophen-5-yl)-2,1,3-benzothiadiazole]-2',2''-diyl) (P3HT-b-PFTBT). Block copolymers can self-assemble into well-ordered nanostructures ideal for photovoltaic applications. When utilized as the photovoltaic active layer, P3HT-b-PFTBT block copolymer devices demonstrate thermal stability and photoconversion efficiency of 3% well beyond devices composed of the constituent polymer blends. Resonant soft X-ray scattering (RSOXS) is used to elucidate the structural origin for efficient block copolymer photovoltaics. Energy tuning in soft X-ray ranges gives RSOXS chemical sensitivity to characterize organic thin films with compositionally similar phases or complicated multiphase systems. RSOXS reveals that the remarkable performance of P3HT-b-PFTBT devices is due to self-assembly into nanoscale in-plane lamellar morphology, which not only establishes an equilibrium microstructure amenable for exciton dissociation but also provides pathways for efficient charge transport. Furthermore, we find evidence that covalent control of donor/acceptor interfaces in block copolymers has the potential to promote charge separation and optimize the photoconversion process by limiting charge recombination. To visualize the nanostructure in organic thin films, we introduce low energy-loss energy-filtered transmission electron microscopy (EFTEM) as an important alternative approach to generate contrast from differences in optoelectronic properties and enable chemical imaging of organic materials. The widely-studied polymer/fullerene system is used as a test sample to demonstrate the application of this technique for structure characterization in the active layer of organic solar cells. In addition, well-ordered equilibrium nanostructures and covalent control of donor/acceptor interfaces make P3HT-b-PFTBT an excellent model for studying the effect of crystalline texture in the active layer on charge transport and photovoltaic performance. Solvent additives are applied to induce a drastic texture change from mainly face-on to edge-on orientations in crystalline P3HT domains of block copolymer thin films. We find that P3HT-b-PFTBT block copolymer devices demonstrate similar optimal performance, regardless of the dramatic changes in the predominant crystalline orientations adopted in P3HT domains. Our results provide further insights into the molecular organization required for efficient charge transport and device operation.

Author: Yongfang Li
Publisher: Springer
ISBN: 3319168622
Category : Technology & Engineering
Languages : en
Pages : 402

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Book Description
This volume reviews the latest trends in organic optoelectronic materials. Each comprehensive chapter allows graduate students and newcomers to the field to grasp the basics, whilst also ensuring that they have the most up-to-date overview of the latest research. Topics include: organic conductors and semiconductors; conducting polymers and conjugated polymer semiconductors, as well as their applications in organic field-effect-transistors; organic light-emitting diodes; and organic photovoltaics and transparent conducting electrodes. The molecular structures, synthesis methods, physicochemical and optoelectronic properties of the organic optoelectronic materials are also introduced and described in detail. The authors also elucidate the structures and working mechanisms of organic optoelectronic devices and outline fundamental scientific problems and future research directions. This volume is invaluable to all those interested in organic optoelectronic materials.

Author: Vivian W. W. Yam
Publisher: Springer Science & Business Media
ISBN: 3642149359
Category : Science
Languages : en
Pages : 245

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Book Description
A major global issue that the world is facing today is the upcoming depletion of fossil fuels and the energy crisis. In 1998, the global annual energy consumption was 12. 7 TW; of which 80% was generated from fossil fuels. This also translates into huge annual emissions of CO that leads to massive environmental problems, 2 particularly the global warming, which could be disastrous. Future global annual energy needs are also estimated to rise dramatically. A major challenge confronting the world is to ?nd an additional 14–20 TW by 2050 when our energy reserves based on fossil fuels are vanishing. The massive demand for energy would require materials and/or processes that would help to provide new sources of clean ren- able energy or to develop processes that would harvest energy or to better utilize energy in an ef?cient manner. The present monograph, WOLEDs and Organic Photovoltaics – Recent Advances and Applications, focuses on a very important and timely subject of topical interest that deals with the more ef?cient use of energy through white organic light-emitting diodes (WOLEDs) for solid-state lighting and the development of clean sources of renewable energy through the harvesting of light energy for conversion into electrical energy in organic photovoltaics. While LED solid-state lighting and photovoltaics have been dominated by inorganic semiconductor materials and silicon-based solar cells, there have been growing interests in the development of WOLEDs and organic photovoltaics.

Author: Paul Barber Armstrong
Publisher:
ISBN:
Category :
Languages : en
Pages : 232

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Book Description
The harvesting of solar energy using photovoltaics has the potential to provide a significant portion of the world's energy. For this to happen, the cost per watt of power produced from photovoltaics must decrease. Excitonic solar cells, including organic solar cells and dye-sensitized solar cells, have the potential to provide the necessary cost savings. However, power conversion efficiencies must be improved before these devices can become practical. This dissertation describes the implementation of several strategies to improve the efficiency of organic polymer and dye-sensitized solar cells. Chapter 1 provides an introduction to current research on excitonic solar cells with a focus on organic polymer and dye-sensitized cells. The detailed mechanisms of photocurrent generation in each type of cell are discussed, and the factors that determine efficiencies are outlined. In addition, an overview of the progress over the last decade in research on polymer photovoltaics is given. Finally, the future prospects for achieving high efficiency devices are described. Chapter 2 details a strategy for controlling the morphology of photovoltaic blends of conjugated polymers and small molecule perylene diimide dyes. Blends of these two materials are subject to excessive phase separation that decreases photovoltaic performance. The development of compatibilizers that alleviate this phase separation is described. A diblock copolymer of poly(3-hexylthiophene) (P3HT) and a perylene diimide (PDI) side chain polymer is an effective compatibilizer. Addition of this material to blends of P3HT and PDI suppresses the formation of micron-sized crystals and results in a 50% improvement in solar cell efficiency. The synthesis of a diblock copolymer of poly(3-(4-octylphenyl)thiophene) and the PDI side chain polymer is also described. This material functions as a compatibilizer, but does not allow for improved photovoltaic efficiency. Chapter 3 describes the synthesis and characterization of a low bandgap conjugated polymer with thermally removable solubilizing groups. Following solution-based deposition of thin films of this polymer, heat can induce the cleavage and evaporation of the alkyl solubilizing chains, resulting in an insoluble film. The optical properties change considerably during this process: the bandgap decreases, and the absorption coefficient increases dramatically. These properties were exploited to fabricate bilayers of the low bandgap material and a highly fluorescent commercial polymer. Fluorescence resonance energy transfer from the fluorescent material to the low bandgap polymer is efficient over 30 nm. Such a scheme could be utilized to overcome the exciton diffusion bottleneck in layered polymer solar cells. In chapter 4, the synthesis of novel n-type polymers based on PDI monomers is described. With appropriate substitution of alkyl chains, highly rigid perylene benzimidazole ladder polymers can be made soluble in common organic solvents. These materials have exceptionally low-lying LUMOs and possess unusual fluorescence properties. Fully planar perylene ethynylene polymers are also synthesized and characterized. Despite their planarity, data from absorbance and fluorescence spectra suggest that the PDI units in these polymers are poorly coupled electronically. X-Ray diffraction shows that the [pi]-stacking distance varies in these materials depending on the nature of the solubilizing groups and can be decreased through solvent annealing. Chapter 5 describes how light harvesting can be improved in dye-sensitized solar cells by adding a second dye that transfers energy to the primary sensitizing dye. In liquid cells, incorporation of a PDI dye in the liquid electrolyte solution results in a 28% improvement in power conversion efficiency. Energy transfer is at least 50% efficient despite significant quenching of the perylene dye's fluorescence by the iodide redox couple. Efforts to employ energy transfer in solid-state dye-sensitized solar cells are also described. This is more challenging because the solid-state hole transporter is an excellent quencher of fluorescent dyes. However, it is shown that this quenching can be prevented by self-assembling dyes such as fluorescein 548 into a poly(propyleneimine) dendrimer. Unfortunately, processing conditions that allow the dendrimer/dye conjugates to penetrate the pores of the cell's titania films have not yet been found.

Author: Sam-Shajing Sun
Publisher: CRC Press
ISBN: 1351837060
Category : Technology & Engineering
Languages : en
Pages : 916

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Book Description
Recently developed organic photovoltaics (OPVs) show distinct advantages over their inorganic counterparts due to their lighter weight, flexible shape, versatile materials synthesis and device fabrication schemes, and low cost in large-scale industrial production. Although many books currently exist on general concepts of PV and inorganic PV materials and devices, few are available that offer a comprehensive overview of recently fast developing organic and polymeric PV materials and devices. Organic Photovoltaics: Mechanisms, Materials, and Devices fills this gap. The book provides an international perspective on the latest research in this rapidly expanding field with contributions from top experts around the world. It presents a unified approach comprising three sections: General Overviews; Mechanisms and Modeling; and Materials and Devices. Discussions include sunlight capture, exciton diffusion and dissociation, interface properties, charge recombination and migration, and a variety of currently developing OPV materials/devices. The book also includes two forewords: one by Nobel Laureate Dr. Alan J. Heeger, and the other by Drs. Aloysius Hepp and Sheila Bailey of NASA Glenn Research Center. Organic Photovoltaics equips students, researchers, and engineers with knowledge of the mechanisms, materials, devices, and applications of OPVs necessary to develop cheaper, lighter, and cleaner renewable energy throughout the coming decades.

Author: Jessica D. Douglas
Publisher:
ISBN:
Category :
Languages : en
Pages : 188

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Book Description
The chemical structure of conjugated semiconducting materials strongly influences the performance of organic photovoltaic (OPV) devices. Thus a good understanding of the structure-function relationships that govern the optoelectronic and physical properties of OPV materials is necessary. In this dissertation, organic polymers and small molecules are evaluated in terms of OPV device output parameters, and molecular design rules are elucidated. The development of molecules with alternating electron-rich and electron-deficient backbone units provides materials with suitable optoelectronic properties for OPVs and favorable modularity for organic semiconductor design. The choice of specific aromatic units and side chains for conjugated materials are shown to modulate the energy levels and architecture of OPV devices, affecting each of the four mechanistic steps of OPV operation. In Chapter 2, the relationship between molecular packing parameters and the bulkiness of aliphatic solubilizing group extending away from a polymer backbone is elucidated, and high-performance OPV devices are achieved. In Chapter 3, the inclusion of a post-processing functionality on a polymer side chain is found to have a positive effect on the bulk morphology and overall performance of OPV devices. In Chapter 4, the influence of electron-withdrawing and quinoidal monomers on the optoelectronic properties of conjugated polymers is established, and energy level modulation is shown to affect the electron accepting and donating capabilities of OPV materials in a blended device. In Chapter 5, small molecules are designed with complementary light absorption properties in order to investigate a rarely observed charge generation mechanism.

Author: Fei Huang
Publisher: Royal Society of Chemistry
ISBN: 1782622306
Category : Science
Languages : en
Pages : 422

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Book Description
Polymer solar cells have gained much attention as they offer a potentially economic and viable way of commercially manufacturing lightweight, flexible and low-cost photovoltaics. With contributions from leading scientists, Polymer Photovoltaics provides an international perspective on the latest research for this rapidly expanding field. The book starts with an Introduction to polymer solar cells and covers several important topics that govern their photovoltaic properties including the chemistry and the design of new light harvesting and interfacial materials and their structure-property relationship; the physics for photocurrent generation in the polymer solar cells; new characterization tools to study morphology effect on the property of donor/acceptor bulk heterojunctions; new device concepts such as tandem cells and semi-transparent cells and advanced roll-to-roll processes for large-scale manufacturing of polymer solar cells. Written by active researchers, the book provides a comprehensive overview of the recent advancements in polymer solar cell technology for both researchers and students that are interested in this field.

Author: Christoph Joseph Brabec
Publisher: Springer Science & Business Media
ISBN: 9783540004059
Category : Technology & Engineering
Languages : en
Pages : 320

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Book Description
The present volume describes and explains the fundamentals of organic/plastic solar cells in a manner accessible to both researchers and students. It provides an up-to-date and comprehensive account of these materials and corresponding devices, which will play a key role in future solar energy systems.