Download or read book Controlling the Morphology of Solution processed Bulk Heterojunction Photovoltaics written by Kevin Andrew Sivula and published by . This book was released on 2007 with total page 358 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Morphology Control in Polymer Light Emitting Diodes and Molecular Bulk heterojunction Photovoltaics written by Kenneth R. Graham and published by . This book was released on 2011 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The D-A-D based oligomers are observed to readily form aggregates that lead to decreases in device performance. To combat this problem, oligomers with bulky or cross-linkable end-groups are incorporated into PLEDs. Although neither strategy is shown to reduce aggregation, the cross-linkable systems allow for solution-processed multilayer PLEDs to be obtained. The family of Pt-porphyrins incorporated into PLEDs was designed with two primary purposes; extending the emission wavelength further into the near-IR and optimizing the molecular structure to both decrease aggregation and increase quantum yield. The second portion of this dissertation focuses on controlling morphology in solution-processed molecular BHJ photovoltaic cells through two different methods. The first method involves the incorporation of solvent additives with known solubility parameters to develop a predictable method of morphology control. The second method involves the use of asymmetric oligomers to more predictably control the crystallization kinetics and thus provide the ability to finely tune the film morphology.

Download or read book Optimizing Morphology of Bulk Heterojunction Polymer Solar Cells written by Jing Gao and published by . This book was released on 2014 with total page 100 pages. Available in PDF, EPUB and Kindle. Book excerpt: The performance of bulk heterojunction polymer solar cells is profoundly influenced by the spatial arrangements of microstructure at various length scales in its photo-active layer, referred to as morphology. Due to their complex chemical structures, polymers usually exhibits low crystallinity and carrier mobility, leading to a limited thickness ~100 nm of the active layer for a typical polymer solar cell. Such thin films are incompatible with the prevailing large-area coating techniques, thus increasing the difficulty to realize the high-throughput production of polymer-based photovoltaics in industry. On the other hand, for most high-performance low-band-gap polymers, during their film-casting process, processing solvent additives are usually essential for morphology optimization, which help boost device efficiency. However, most commonly-used solvent additives such as 1, 8-Diiodooctane (DIO), are disturbingly reactive to oxygen or water in air, leading to deteriorated performance of devices made under the ambient environment. Therefore, fabrication processes involving DIO have to be limited to an air-free environment, which is quite unfavorable for large-area fabrication techniques, as majority of them are carried on under the ambient environment. Therefore, an efficient air-stable solvent additive would be greatly appreciated in terms of OPV industrialization. As a result, in order to achieve thick active layers as well as to find an air-stable alternative additive for industrial applications, a thorough and systematic study on morphology is necessitated. First, via rational modification of polymer chemical structure(fine-tuning on side chains), new polymers with enhanced structure order (e.g., crystallite size increases from 35 Å to 53 Å) and higher hole mobility (from ~10-5 to ~10-4 cm2/(V*s)) are obtained, enabling thicker optimum active layers ~200 nm with a larger thickness tolerance up to ~350 nm for the corresponding bulk heterojunction devices. This result is of great potential for relaxing the required level of precision in active layer thickness, which has important industrial implications for large-area film deposition. Second, through examining those solvents with a great potential to satisfy the criteria for efficient additives, a new efficient air-stable solvent additive -1,2-dichlorobenzene (DCB) was successfully found for the Diketopyrrolopyrrole-based narrow bandgap polymer under investigation in this work, with a much larger working operation window (up to 80%) and higher device efficiency than DIO. The reason for improved performance lies in higher hole mobility due to polymer crystallinity enhancement in films cast from solution processed by both additives, as demonstrated by Transmission Electron Microscopy (TEM), photoluminescence (PL) and Grazing Incident Wide Angle X-ray Scattering (GIWAXS) results. Small Angle Neutron Scattering (SANS) and UV-visible absorption spectroscopy were also conducted on polymer structures in solution, and their results revealed a novel working mechanism of DCB for morphology control, which involves the modified solution-stage polymer conformations due to the polymer-additive interaction. Upon incorporating DCB into blend solution, the resultant polymer configurations in solution would have a high tendency to preserve into crystalline regions in the as-cast films and this unique way of tuning thin-film morphology via altering polymer conformations in solution has established a new guide for future additive selection in other polymer systems. Results of this manuscript will resolve the current obstacle for high-throughput process in industry and should be of great potential to contribute to practical OPV applications in the near future.

Download or read book Processing property performance Relationships in Solution processed Small Molecule Bulk Heterojunction Organic Solar Cells written by Alexander Sharenko and published by . This book was released on 2014 with total page 85 pages. Available in PDF, EPUB and Kindle. Book excerpt: It is well established that the specifics of the bulk heterojunction morphology (phase separation, crystallinity, etc.) profoundly affect BHJ OPV device PCE. Controlling the BHJ morphology is thus of great importance. Using in-situ thermal annealing grazing incidence wide and small angle x-ray scattering it was discovered that the driving force for phase separation in BHJ OPV systems utilizing small molecule donor materials and functionalized fullerene acceptors is the crystallization of the small molecule donor material. Additionally, it was shown that this crystallization process, and therefore the development of the bulk heterojunction morphology and device performance, can be controlled by using commercially available nucleating agents designed for the clarifying of isotactic polypropylene.

Download or read book Examining and Controlling the Morphology of the Photoactive Layer of Organic Photovoltaic Devices written by Sameer Vajjala Kesava and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Electronic devices such as solar cells, transistors and light-emitting diodes (LEDs) fabricated using organic semiconductors offer a potential feasible alternative to their inorganic counterparts due to several advantages such as ease of processing (ink-jet printing, roll-to-roll processing), flexibility and excellent control over the electronic properties through chemical modifications. Compared to the inorganic semiconductors, however, the performance of organic semiconductor-based electronic devices are much lower. For example, in the case of photovoltaic devices (solar cells), the power-conversion efficiencies are still lower (7%-10%) compared to that of inorganic solar cells (> 25%). The efficiency of a solar cell is determined, among other factors, to a significant extent by the morphology of the active layer, the thin film where photons are absorbed and charges generated. Even though significant improvement in the efficiencies have been achieved, mainly through band-gap engineering and processing optimization, a fundamental understanding of the structural and morphological effects of the active layer on the performance of organic photovoltaic devices remains obscured. In this work, the focus is on examining the structure-function relationships in solution-processed bulk-heterojunction organic photovoltaic devices and development of processing techniques for device optimization. A bulk-heterojunction device is formed by mixing of donor-acceptor semiconductors, and the subsequent structure formed in the active layer is dictated by the miscibility and crystallization of the components, which are functions of processing conditions. Excitons (electron-hole pairs bound by coulombic forces) formed in the donor semiconductor upon absorption of light have a diffusion length of around 5-10 nm before recombination occurs. Thus the structural length scales formed in the active layer determine the number of excitons that can dissociate into charges. We have examined the microstructure of poly(3-hexyl thiophene) (P3HT) donor and phenyl-C61-butyric acid methyl ester (PC61BM) acceptor mixture using grazing incidence small angle X-ray scattering (GISAXS) and energy-filtered transmission electron microscopy (EFTEM) to characterize the in-plane structural length scales for various processing conditions such as annealing temperatures and spin-casting solvents. Our results show that the structural length scales are driven by self-limiting P3HT crystallization upon thermal annealing, which correlate to the internal quantum efficiencies of the devices. In contrast, it has been reported in the case of poly[2,5-bis(3-hexadecylthiophen-2-yl)thieno[3,2-b]thiophene] (PBTTT)/ fullerene mixtures that thermal annealing results in crystallization of PBTTT with unconstrained lateral dimensions causing coarsening of the in-plane characteristic length scales. Thus the morphological evolution in polymer/fullerene solar cells, and consequently device performance, depends on the crystallization motif of the polymer. The microstructure resulting from mixing of donor-acceptor semiconductors can yield distinctive donor-acceptor interfaces that affect charge separation and recombination. Our studies utilizing a low band-gap poly[(4,4'-bis(2-ethylhexyl)dithieno[3,2-b:2',3'-d]germole)-2,6-diyl-alt-(2,1,3-benzothiadiazole)-4,7-diyl] (PGeBTBT) donor and PC71BM acceptor examine the effects of mixing on the charge generation in a device. Composition of mixed phases ascertained qualitatively and quantitatively using EFTEM and resonance soft X-ray scattering (RSOXS) show that the concentration of polymer in the mixed phase decreases as fullerene concentration in the mixture is increased. This resulted in a concomitant increase in the device performance. Similarly, photo-induced absorption studies carried out using ultrafast spectroscopy show increase in polaron concentration with increase in purity of the mixed phase. Grazing-incidence wide-angle X-ray scattering (GIWAXS) data show a change in fullerene aggregation with increase in fullerene concentration in the mixture. This indicates that adding polymer to the mixed phase results in dispersal of fullerene, and consequently, changing the local environment of the polymer affects formation of charge-transfer states and subsequent dissociation into individual charges. Thus, high interfacial area that is formed upon intimate mixing of polymer/fullerene, considered ideal for efficient exciton dissociation, counteracts through high charge recombination. Our results show that the composition of mixed phases affects charge separation at the interface consequently affecting device performance of organic photovoltaics. Another important aspect that has been shown to affect device performance of organic photovoltaics is the orientation of polymer crystals with respect to the substrate. For example, P3HT predominantly orients in an edge-on configuration, i.e., with the [pi]-[pi] bond stacking direction parallel to the substrate. It is hypothesized that out of plane [pi]-[pi] stacking, called face-on orientation, is important for effective charge transport. One way to achieve enhancement of face-on orientation is by directional crystallization which has been shown to be very effective for P3HT -- in this case, directional crystallization from solution. In this context, 'zone-annealing' is relevant as it has been employed to directionally crystallize polymers. In this work, we designed and developed the zone-annealing equipment, which can yield thermal gradients greater than 60°C/mm. Preliminary results from GIWAXS experiments on P3HT/PC61BM thin films show anisotropy in the structure and a moderate enhancement of face-on orientated P3HT crystallites. This technique was extended to organic field-effect transistors (OFET) to enhance charge mobilities through directional crystallization of organic semiconductors. In case of P3HT, the increment in charge mobilities was by a factor of 2 upon zone-annealing. However, in the case of organic small molecule semiconductor, 2,7-dioctyl[1]benzo- thieno[3,2-b][1] benzothiophene (C8-BTBT) , highly aligned crystalline domains were obtained -- a very promising result for fabricating high mobility OFETs. Thus, the zone-annealing technique provides a handle for controlling the morphology of organic thin film electronic devices.

Download or read book Studies on Controlling the Morphology of an Organic Bulk heterojunction Photovoltaic Device to Improve Its Efficiency written by Kelly Rene McLeod and published by . This book was released on 2013 with total page 46 pages. Available in PDF, EPUB and Kindle. Book excerpt: A systematic study of the effects of alteration of processing parameters in combination with incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules on the properties and structure of bulk heterojunction organic photovoltaic cells made from P3HT:PCBM blends was undertaken. On implementing the correct processing protocol, incorporation of POSS molecules with specific structures resulted in considerable enhancement in cell efficiencies. Octaaminophenyl POSS incorporation resulted in a 20% increase in cell efficiency over the control and caused the formation of crystalline, fiber-like structures in the active layer of the photovoltaic cell.--P. iv.

Download or read book Loss Mechanisms in Solution Processed Small Molecule Bulk Heterojunction Solar Cells written by Christopher Michael Proctor and published by . This book was released on 2015 with total page 204 pages. Available in PDF, EPUB and Kindle. Book excerpt: Using a combination of electrical characterization techniques, it was found that two of the primary loss mechanisms in solar cells made from solution processed small molecules include field dependent generation and the recombination of free charge carriers. While field dependent generation is a significant loss mechanism in some cases, it was shown that it can also be completely overcome by careful control of the film morphology. The reduction of field dependent generation was found to be correlated with progressively purer and more ordered domains within the small molecule film.

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 Morphology Studies of Polymer Bulk Heterojunction Solar Cells written by Ji Sun Moon and published by . This book was released on 2011 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: This thesis is a study of the morphology of polymer:fullerene BHJ, one of the most critical and challenging parts of high efficiency polymer solar cells. To discover the morphology, cross-section as well as top-down transmission electron microscopy were used. The contrast was achieved by utilizing phase contrast microscopy. Thermal annealing, dependence of BHJ thickness, processing additives, solution sequential process and solution sequential process with the use of cosolvent that affects/controls the BHJ morphology are studied in detail.

Download or read book Handbook of Conducting Polymers Fourth Edition 2 Volume Set written by John R. Reynolds and published by CRC Press. This book was released on 2019-11-14 with total page 1488 pages. Available in PDF, EPUB and Kindle. Book excerpt: In the last 10 years there have been major advances in fundamental understanding and applications and a vast portfolio of new polymer structures with unique and tailored properties was developed. Work moved from a chemical repeat unit structure to one more based on structural control, new polymerization methodologies, properties, processing, and applications. The 4th Edition takes this into account and will be completely rewritten and reorganized, focusing on spin coating, spray coating, blade/slot die coating, layer-by-layer assembly, and fiber spinning methods; property characterizations of redox, interfacial, electrical, and optical phenomena; and commercial applications.

Download or read book Third Generation Photovoltaics written by Vasilis Fthenakis and published by BoD – Books on Demand. This book was released on 2012-03-16 with total page 248 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaics have started replacing fossil fuels as major energy generation roadmaps, targeting higher efficiencies and/or lower costs are aggressively pursued to bring PV to cost parity with grid electricity. Third generation PV technologies may overcome the fundamental limitations of photon to electron conversion in single-junction devices and, thus, improve both their efficiency and cost. This book presents notable advances in these technologies, namely organic cells and nanostructures, dye-sensitized cells and multijunction III/V cells. The following topics are addressed: Solar spectrum conversion for photovoltaics using nanoparticles; multiscale modeling of heterojunctions in organic PV; technologies and manufacturing of OPV; life cycle assessment of OPV; new materials and architectures for dye-sensitized solar cells; advances of concentrating PV; modeling doped III/V alloys; polymeric films for lowering the cost of PV, and field performance factors. A panel of acclaimed PV professionals contributed these topics, compiling the state of knowledge for advancing this new generation of PV.

Download or read book Controlled Morphology in Bulk Heterojunction Polymer and Perovskite Solar Cells written by Yan Sun and published by . This book was released on 2016 with total page 162 pages. Available in PDF, EPUB and Kindle. Book excerpt: Bulk heterojunction (BHJ) polymer solar cells constitute an emerging approach to a low cost, solution processable, and highly scalable renewable energy avenue. However, one of the major challenges limiting the broad applicability of these solar cells is their lower device efficiencies compared to their inorganic counterparts. In this regard, much effort has been dedicated to optimizing the efficiencies by developing new high-performance materials and fine tuning the BHJ blend morphology via various processing methods. This study presents a molecular level understanding of what controls the device performance.In the first part, a novel fulleropyrrolidine derivative C60-fused N-(3-methoxypropyl)-2-(carboxyethyl)-5-(4-cyanophenyl) fulleropyrrolidine (NCPF) was synthesized and blended with a conjugated polymer poly(3-hexylthiophene) (P3HT) for applications of BHJ polymer solar cells. NCPF has a good solubility in common organic solvents and comparable electronic properties with the widely used acceptor [6,6]-phenyl-C61-butyric acid methyl ester (PCBM). A short term thermal annealing induced enhancement in device performance was found to be associated with improved crystallization of polymer within blend thin films and correspondingly increased hole mobility. The long term annealing study showed that P3HT:NCPF blends had superior thermal stability compared to P3HT:PCBM blends. In the second part, we demonstrate the compatibilization effect of a rod-coil block copolymer (BCP) in different polymer:fullerene derivative blend systems. AFM results and GIWAXS analyses revealed that the addition of BCP into the blend thin films effectively altered the thin film nanostructure and polymer crystalline structure. Moreover, higher device efficiencies were obtained in blends containing block copolymer compatibilizer. The improvement in performance was then ascribed to the morphological changes in the polymer:fullerene blends.The final study deals with the application of a simple, high throughput and roll-to-roll compatible process, zone annealing, to process polymer:fullerene BHJ blends. By morphological study, we established a regime in which interpenetrating phase separated morphology was obtained via zone annealing that exhibited no overgrown fullerene crystallites. Moreover, we extend the use of zone annealing method to perovskite materials, i.e. inorganic--organic hybrid lead halide perovskites. The zone annealed perovskite film morphology exhibits a transition from densely packed structures to dendritic crystallizations with increasing sample annealing velocity. This transition shifts to lower speed in higher temperature condition. By varying temperature and the sweeping speed, large grains were observed in zone annealed samples. Collectively, these studies provide a more fundamental and deeper understanding of the relationships between materials, processing, morphology and performance of thin film solar cells.

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 832 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 Smart Polymer Nanocomposites written by Deepalekshmi Ponnamma and published by Springer. This book was released on 2017-03-06 with total page 404 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers smart polymer nanocomposites with perspectives for application in energy harvesting, as self-healing materials, or shape memory materials. The book is application-oriented and describes different types of polymer nanocomposites, such as elastomeric composites, thermoplastic composites, or conductive polymer composites. It outlines their potential for applications, which would meet some of the most important challenges nowadays: for harvesting energy, as materials with the capacity to self-heal, or as materials memorizing a given shape.The book brings together these different applications for the first time in one single platform. Chapters are ordered both by the type of composites and by the target applications. Readers will thus find a good overview, facilitating a comparison of the different smart materials and their applications. The book will appeal to scientists in the fields of chemistry, material science and engineering, but also to technologists and physicists, from graduate student level to researcher and professional.

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 Morphology Characterization of Low Band Gap Polymer based Organic Photovoltaics written by Feng Liu and published by . This book was released on 2014 with total page 110 pages. Available in PDF, EPUB and Kindle. Book excerpt: In bulk heterojunction (BHJ) thin film organic photovoltaics (OPV), morphology control is critical to obtain good device efficiency. Nanoscale phase separation that creates bicontinuous interpenetrating structure on a size scale commensurate with exciton diffusion length (~10 nm) is thought to be the ideal morphology. Results obtained from this work indicate that morphology can be affected by chemical structure of the polymer, processing conditions, blending ratio and post treatments. Physical properties of the material, such as crystallinity, crystal orientation, material interactions and miscibility, surface energy and particle aggregations are critical for determining the morphology and thus the device performance. Previous investigations on poly(3-hexylthiophene) (P3HT) based OPV study yielded a solid structure-property relation. However, different physical properties of polymers preclude the direct transfer of P3HT knowledge to better-performing low band gap polymer OPVs, for which the morphology is directly obtained from solvent casting. This thesis discovered commonalities of low band gap polymer based OPVs. Two important photoactive polymers (PTB7 and DPP) are chosen, each with specific properties. In particular, the function of additives in morphology controls was investigated. Fibril formation at the ~10 nanometer scale proved crucial for obtaining high performance in solar cells. Besides these typical crystalline structures, mixed regions also proved important. The mesh size of the fibril network largely determined the current of the device, and thus determined the power conversion efficiency. The aggregation behavior of polymer chains also influenced the BHJ morphology. Besides the fibril network picture, we also observed multi-length scaled morphology in PTB7 based OPV systems.

Download or read book Organic Solar Cells written by Qiquan Qiao and published by CRC Press. This book was released on 2017-12-19 with total page 426 pages. Available in PDF, EPUB and Kindle. Book excerpt: Current energy consumption mainly depends on fossil fuels that are limited and can cause environmental issues such as greenhouse gas emissions and global warming. These factors have stimulated the search for alternate, clean, and renewable energy sources. Solar cells are some of the most promising clean and readily available energy sources. Plus, the successful utilization of solar energy can help reduce the dependence on fossil fuels. Recently, organic solar cells have gained extensive attention as a next-generation photovoltaic technology due to their light weight, mechanical flexibility, and solution-based cost-effective processing. Organic Solar Cells: Materials, Devices, Interfaces, and Modeling provides an in-depth understanding of the current state of the art of organic solar cell technology. Encompassing the full spectrum of organic solar cell materials, modeling and simulation, and device physics and engineering, this comprehensive text: Discusses active layer, interfacial, and transparent electrode materials Explains how to relate synthesis parameters to morphology of the photoactive layer using molecular dynamics simulations Offers insight into coupling morphology and interfaces with charge transport in organic solar cells Explores photoexcited carrier dynamics, defect states, interface engineering, and nanophase separation Covers inorganic–organic hybrids, tandem structure, and graphene-based polymer solar cells Organic Solar Cells: Materials, Devices, Interfaces, and Modeling makes an ideal reference for scientists and engineers as well as researchers and students entering the field from broad disciplines including chemistry, material science and engineering, physics, nanotechnology, nanoscience, and electrical engineering.