Download or read book Improving Device Efficiencies in Organic Photovoltaics Through the Manipulation of Device Architectures and the Development of Low bandgap Materials written by Andrew Hideo Rice and published by . This book was released on 2013 with total page 94 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past two decades, vast amounts of research have been conducted in the pursuit of suitable organic semiconductors to replace inorganic materials in electronic applications due to their advantages of being lightweight, flexible, and solution-processible. However, before organic photovoltaics (OPVs) can be truly competitive and commercially viable, their efficiencies must be improved significantly. In this examination, we pursue higher efficiency OPVs in two different ways. Our attempts focus on 1) altering the microstructure of devices to improve charge dissociation, charge transport, and our understanding of how these devices function, and 2) tailoring materials to achieve optimal band gaps and energy levels for use in organic electronics. First, we demonstrate how the vertical morphology of bulk heterojunction (BHJ) solar cells, with an active layer consisting of self-assembled poly(3-hexylthiophene) (P3HT) nanowires and (6,6)-phenyl C61-butyric acid methyl ester (PCBM), can be beneficially influenced. Most device fabrication routes using similar materials employ an annealing step to influence active layer morphology, but this process can create an unfavorable phase migration where P3HT is driven toward the cathode. In contrast, we demonstrate devices that exhibit an increase in relative fullerene concentration at the top of the active layer by introducing the donor phase as a solid nanowire in the active layer solution and altering the pre-spin drying time. X-ray photoelectron spectroscopy (XPS) and conductive and photoconductive atomic force microscopy (cAFM and pcAFM) provide detailed information about how the surface of the active layer can be influenced; this is done by tracking the concentration and alignment of P3HT and PCBM domains. Using this new procedure, devices are made with power conversion efficiencies surpassing 2%. Additionally, we show that nanowires grown in the presence of the fullerene perform differently than those that are grown and mixed separately; exposure to the nanowire during self-assembly may allow the fullerene to coat nanowire surfaces and influence the photocurrent within the device. Furthermore, because we are able to carefully control the regioregularity of our P3HT, we are able to produce a series of nanowires with regioregularities ranging between 93% and 99%. X-ray diffraction (XRD) shows that as the regioregularity of the polymer increases, the coherent domain size along the long-axis of the nanowires also becomes larger. When organic field effect transistors (OFETs) are made from these materials, the hole mobility of the nanowire films also has a positive correlation with regioregularity. As the domains within the nanowires grow larger, the frequency of domain boundaries decreases, allowing charges to percolate more efficiently along the nanowire. Additionally, we show that by introducing C60 into the active layer of P3HT:PCBM devices, we can modulate the crystal habit of the PCBM domains. Using optical microscopy and UV-vis absorption spectroscopy, we demonstrate that C60 additions alter the crystal morphology and greatly reduce the size of fullerene crystallites that are observed after extended annealing times and under aggressive aging conditions. We also show by fabricating organic field-effect transistors (OFETs) from PCBM:C60 blends that the incorporation of C60 does not adversely affect the electron mobility in these films. Finally, we show that as C60 is incorporated into P3HT:PCBM OPVs, devices become more thermally stable and do not degrade in performance as rapidly as traditional P3HT:PCBM blends. Lastly, the synthesis of four alternating copolymers using benzo[2,1-b;3,4-bʹ]dithiophene (BDP) as the common donor unit is presented. Incorporating BDP, which consists of fused dithiophene units with a benzene ring, into these polymers should produce a low-lying highest occupied molecular orbital (HOMO) energy level. Low-lying HOMO levels are desirable to produce high open circuit voltages (V[subscript OC]) in organic BHJ photovoltaic devices. The preliminary results of their performance in solar cells, using PCBM as the electron acceptor, is presented. The V[subscript OC] values follow the expected trend: increasing with decreasing HOMO level of the polymer. High V[subscript OC] values of 0.81 and 0.82 V have been obtained from two polymers: PBDPBT and PBDPDPP. The highest initial power conversion efficiency (PCE) achieved in these unoptimized devices was 1.11% due to relatively low J[subscript sc] values. The variation observed in the J[subscript sc] values between the four polymers is discussed. Device performance is expected to increase with optimization of processing conditions for the devices.

Download or read book Organic Photovoltaics written by Christoph Brabec and published by John Wiley & Sons. This book was released on 2011-09-22 with total page 597 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Organic Photovoltaics written by Sam-Shajing Sun and published by CRC Press. This book was released on 2017-12-19 with total page 916 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Progress in High Efficient Solution Process Organic Photovoltaic Devices written by Yang Yang and published by Springer. This book was released on 2015-02-26 with total page 417 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book presents an important technique to process organic photovoltaic devices. The basics, materials aspects and manufacturing of photovoltaic devices with solution processing are explained. Solution processable organic solar cells - polymer or solution processable small molecules - have the potential to significantly reduce the costs for solar electricity and energy payback time due to the low material costs for the cells, low cost and fast fabrication processes (ambient, roll-to-roll), high material utilization etc. In addition, organic photovoltaics (OPV) also provides attractive properties like flexibility, colorful displays and transparency which could open new market opportunities. The material and device innovations lead to improved efficiency by 8% for organic photovoltaic solar cells, compared to 4% in 2005. Both academic and industry research have significant interest in the development of this technology. This book gives an overview of the booming technology, focusing on the solution process for organic solar cells and provides a state-of-the-art report of the latest developments. World class experts cover fundamental, materials, devices and manufacturing technology of OPV technology.

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 WOLEDs and Organic Photovoltaics written by Vivian W. W. Yam and published by Springer Science & Business Media. This book was released on 2010-11-19 with total page 245 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

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 Organic Solar Cells written by Wallace C.H. Choy and published by Springer Science & Business Media. This book was released on 2012-11-19 with total page 268 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic solar cells have emerged as new promising photovoltaic devices due to their potential applications in large area, printable and flexible solar panels. Organic Solar Cells: Materials and Device Physics offers an updated review on the topics covering the synthesis, properties and applications of new materials for various critical roles in devices from electrodes, interface and carrier transport materials, to the active layer composed of donors and acceptors. Addressing the important device physics issues of carrier and exciton dynamics and interface stability and novel light trapping structures, the potential for hybrid organic solar cells to provide high efficiency solar cells is examined and discussed in detail. Specific chapters covers key areas including: Latest research and designs for highly effective polymer donors/acceptors and interface materials Synthesis and application of highly transparent and conductive graphene Exciton and charge dynamics for in-depth understanding of the mechanism underlying organic solar cells. New potentials and emerging functionalities of plasmonic effects in OSCs Interface Degradation Mechanisms in organic photovoltaics improving the entire device lifetime Device architecture and operation mechanism of organic/ inorganic hybrid solar cells for next generation of high performance photovoltaics This reference can be practically and theoretically applied by senior undergraduates, postgraduates, engineers, scientists, researchers, and project managers with some fundamental knowledge in organic and inorganic semiconductor materials or devices.

Download or read book Clean Electricity From Photovoltaics written by Mary D Archer and published by World Scientific. This book was released on 2001-06-04 with total page 870 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaic cells provide clean, reversible electrical power from the sun. Made from semiconductors, they are durable, silent in operation and free of polluting emissions. In this book, experts from all sectors of the PV community — materials scientists, physicists, production engineers, economists and environmentalists — give their critical appraisals of where the technology is now and what its prospects are./a

Download or read book Polymer polymer blends in organic photovoltaic and photodiode devices written by Yuxin Xia and published by Linköping University Electronic Press. This book was released on 2019-01-04 with total page 78 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics devices (OPV) have attracted attentions of scientist for their potential as inexpensive, lightweight, flexible and suitable for roll-to-roll production. In recent years, considerable attention has been focused on new acceptor materials, either polymeric or small molecules, to replace the once dominating fullerene derivatives. The emergence of numerous new non-fullerene materials has driven power conversion efficiency (PCE) up to 17%, attracting more and more interests of commercialization. Polymer acceptors with more morphology stability, more absorption and more desired energy levels has been intensively studied and show great potential for large area and low-cost production in the future. OPV at this moment is not yet competitive with inorganic solar cells in PCE but is more attractive in flexibility, low weight and semitransparency. In this thesis, some basic knowledges of OPV is introduced in the first few chapters, while the next chapters are focusing on polymer-polymer blends and investigating novel structures and techniques for large scale production of solar cells and photodetectors aiming at maximizing these advantages to compete with inorganic counterpart. Thermal annealing effects on polymer-polymer solar cells based is studied. Annealed devices show doubled power conversion efficiency compared to non-annealed devices. Based on the morphology—mobility examination, we conclude that the better charge transport is achieved by higher order and better interconnected networks of the bulk heterojunction in the annealed active layers. The annealing improves charge transport and extends the conjugation length of the polymers, which do help charge generation and meanwhile reduce recombination. The blend of an amorphous polymer and a semi-crystalline polymer can thus be modified by thermal annealing to double the power conversion efficiency. A novel concept of all-polymer organic photovoltaics device is demonstrated in this thesis where all the layers are made out of polymers. We use PEDOT:PSS as semitransparent anode and polyethyleneimine modified PEDOT:PSS as semitransparent cathode, both of which are slot-die printed on polyethylene terephthalate(PET). Active layers are deposited on cathode and anode surfaces by spin coating separately. These layers are then joined through a roll-to-roll compatible lamination process. This forms a semitransparent and flexible solar cell. By laminating a thin layer acceptor polymer to a thick polymer-polymer blend, we can further improve the performance by reducing traps comparing to laminating blend to blend. Flexible and semitransparent all-polymer photodiodes with different geometries can be fabricated through lamination. By choosing high band gap polymers and appropriate combination of two or more polymers, organic photodiode with low noise and high specific detectivity can be obtained. Comparison between bilayer and bulk heterojunction devices gives better understanding of the origin of noise and provides ways to improve the performance of photodiodes as detector. Noise level is a critical parameter for photodetectors. The difficulties of measuring the noise of photodetectors make some researchers prefer the estimated shot noise as the dominating one and ignore the thermal noise and 1/f noise. The latter two terms are sometimes several orders higher than the former, noting the importance of experimentally measuring noise. The use of semi-transparent photovoltaic devices causes an inevitable loss of photocurrent, as light transmitted has not been absorbed. This trivial effect also leads to a loss of photovoltage, an effect partially due to the lower photocurrent but also due to the geometry of the semitransparent photovoltaic device. We here demonstrate and evaluate this photovoltage loss in semi-transparent organic photovoltaic devices, compared with non-transparent solar cells of the same material. Semi-transparent solar cells in addition introduce photovoltage loss when formed by lamination. We document and analyze these effects for a number of polymer blends in the form of bulk heterojunctions.

Download or read book High Performance Organic Photovoltaics Via Novel Materials Combinations written by and published by . This book was released on 2011 with total page 12 pages. Available in PDF, EPUB and Kindle. Book excerpt: OPV cell efficiencies have increased significantly over the last decade and verified champion efficiencies are currently at 8.3% for both single and multi-junction device types. These increases in efficiency have been driven through the development and optimization of the donor and acceptor materials in bulk heterojunction active layers. Plextronics and Solarmer Energy Inc. are two of the world leading developers of these donor and acceptor materials. Solarmer Energy has reported NREL certified 6.77% efficiencies using optimized low band gap donor materials in combination with PC61BM and PC71BM acceptors and recently reported a champion NREL certified efficiency of 8.1%. Plextronics has reported Newport certified efficiencies of 6.7% using PC71BM acceptors with low band gap materials. In addition, Plextronics has also demonstrated that OPV efficiency of P3HT based materials can be improved by 50% by improving the Voc using alternative acceptors (indene substituted C60 and C70) to PC61BM and PC71BM. However, performance of these alternative acceptors in combination with low band gap materials has not been investigated and the potential for efficiency improvement is evident. In this collaboration, four low band gap donor materials from Solarmer Energy Inc were combined with Plextronics' indene-class acceptors Plextronics' indene substituted C60 and C70 acceptors to demonstrate OPV performance greater than 7%. Two main indene class C60 acceptors (codenamed Mono-indene[C60] Mono-indene[C60], Bis-indene[C60]) were screened with the Solarmer polymers. These four polymers were screened and optimized with the indene class acceptors at both Plextronics and Solarmer. A combination was identified which produced 6.7% (internal measurement) with a Solarmer polymer and a Plextronics fullerene acceptor. This was accomplished primarily by improving the Voc as well as improving the current (Jsc) and FF.

Download or read book Next Generation Multilayer Graded Bandgap Solar Cells written by A. A. Ojo and published by Springer. This book was released on 2018-08-16 with total page 262 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book will guide Photovoltaics researchers in a new way of thinking about harvesting light energy from all wavelengths of the solar spectrum. It closes the gap between general solar cells books and photovoltaics journal articles, by focusing on the latest developments in our understanding of solid-state device physics. The material presented is experimental and based on II-VI thin-film materials, mainly CdTe-based solar cells. The authors describe the use of new device design, based on multilayer graded bandgap configuration, using CdTe-based solar cells. The authors also explain how the photo-generated currents can be enhanced using multi-step charge carrier production. The possibility of fabricating these devices using low-cost and scalable electroplating is demonstrated. The value of electroplating for large area electronic devices such as PV solar panels, display devices and nano-technology devices are also demonstrated. By enabling new understanding of the engineering of electroplated semiconductor materials and providing an overview of the semiconductor physics and technology, this practical book is ideal to guide researchers, engineers, and manufacturers on future solar cell device designs and fabrications. Discusses in detail the processes of growths, treatments, solar cell device fabrication and solid state physics, improving readers’ understanding of fundamental solid state physics; Enables future improvements in CdTe-based device efficiency; Explains the significance of defects in deposited semiconductor materials and interfaces that affect the material properties and resulting device performance.

Download or read book Organic Photovoltaics written by Christoph Joseph Brabec and published by Springer Science & Business Media. This book was released on 2013-11-21 with total page 311 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.

Download or read book Organic Bulk heterojunction Photovoltaic Devices written by Margherita Bolognesi and published by . This book was released on 2013 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research on organic photovoltaic devices (OPV) has developed during the past 30 years, but especially in the last decade it has attracted scientific and economic interest triggered by a rapid increase in power conversion efficiencies. Thanks to the introduction of the bulk heterojunction (BHJ) concept, today BHJ OPV efficiencies are exceeding 9%. This thesis gives an overview on the different possible strategies that could be adopted for a further. improvement of BHJ OPV devices performances. The accurate analysis of the chemical, energetic and physical criteria governing the solar cells functioning allowed to individuate some critical aspects and apply possible solutions by a fine tuning of the materials chemical structures, device processing techniques and device architecture engineering. Even though noit in all cases the applied strategy successfully led to device efficiency improvements, the fundamental understanding of some of the efficiency limiting factors could serve as useful scientific basis for future developments.

Download or read book Photosynthesis inspired Device Architectures for Organic Photovoltaics written by Timothy David Heidel and published by . This book was released on 2010 with total page 166 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic semiconductor photovoltaics offer a promising route to low-cost, scalable, emissions-free electricity generation. However, achieving higher power conversion efficiencies is critical before these devices can play a larger role in our future energy generation landscape. Organic photovoltaic devices are currently limited by two primary challenges: (1) a trade-off between light absorption and exciton diffusion and (2) low open-circuit voltage due to charge recombination at the donor-acceptor interface. In this work, we demonstrate two new device architectures inspired by photosynthesis that aim to overcome these two challenges. First, we overcome the trade-off between light absorption and exciton diffusion by introducing an external light absorbing antenna layer. We model energy transfer from the antenna to the charge generating layers via surface plasmon polariton modes in the interfacial thin silver contact and via radiation into waveguide modes. We experimentally demonstrate devices with both single layer antennas and strongly absorbing resonant cavity antennas. We measure energy transfer efficiency from the antenna layer to the PV active layers as high as 51±10%. We discuss structural design criteria and describe ideal antenna material characteristics. Second, we reduce charge transfer state recombination in organic photovoltaics by inserting a thin interfacial layer at the donor-acceptor interface. The thin interfacial layer creates a cascade energy structure that destabilizes the Coulombically bound charge transfer state formed immediately following exciton dissociation. We nd the optimal interfacial layer thickness to be approximately 1.5 nm. In CuPc/C60 devices, under simulated solar illumination the short-circuit current increased 34%, the open-circuit voltage increased 33%, and the power conversion eciency increased 49%. Thin interfacial layers can also be used to study the physics of exciton separation.

Download or read book Photovoltaics Beyond Silicon written by Senthilarasu Sundaram and published by Elsevier. This book was released on 2024-07-01 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 The Consequences of Materials Distribution and Mixing in Bulk Heterojunction Organic Photovoltaic Devices written by Scott Alan Mauger and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPV) hold the potential to provide low-cost solar energy. OPV devices consist of several stacked layers with the active layer responsible for photon absorption. In a bulk heterojunction (BHJ) active layer, a hole-conducting polymer is intimately mixed with an electron-conducting fullerene. While many device properties are due to the bulk properties of the BHJ, the interactions between the BHJ layer and its surrounding layers also influence device electrical performance. Using multiple techniques including spectroscopic ellipsometry, neutron reflectometry, and near edge x-ray absorption fine structure spectroscopy it is shown that mixing between the BHJ and surrounding layers and the distribution of materials within the layers impact device performance metrics such as open circuit voltage (V(oc)), short circuit current density (J(sc)), and fill factor (FF). First, in a conventional device architecture, at the interface between the BHJ and the underlying poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) hole transport layer (HTL), heating is found to cause mixing and an electrochemical reaction between PEDOT:PSS and the donor polymer poly(3-hexylthiophene) (P3HT), which increases selectivity as seen by increases in V(oc) and compensation voltage. However, in an inverted device architecture this interaction does not occur because of the low PSS concentration on the bottom of the PEDOT:PSS layer. Next, a new HTL polymer is characterized and a poly-fluorinated ionomer (PFI) is used to create a thermally stable, high work function HTL. This high work function HTL is used to achieve improved energy level alignment with the large ionization potential (IP) of low-band-gap polymers. This results in increased V(oc), but J(sc), FF, and ultimately device power conversion efficiency are decreased. Finally, we investigate the role of interfaces on the vertical distribution of materials in the BHJ. High surface energy materials result in an interface that is fullerene rich. With heating, the surface energies of the adjacent layers cause a redistribution of materials in the BHJ. Additionally, metals with a work function equal to or smaller than the electron affinity (EA) of the acceptor fullerene are found to donate charge to the fullerene at the BHJ/cathode interface improving charge selectivity and power conversion efficiency.