Spectroscopic Investigations of Transfer and Transport of Charge Carriers in the Donor/Acceptor Network of Organic Solar Cells PDF Download
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Author: Helene Ahme
Publisher:
ISBN: 9783839607794
Category :
Languages : en
Pages : 137
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Author: Helene Ahme
Publisher:
ISBN: 9783839607794
Category :
Languages : en
Pages : 137
Get Book Here
Book Description
Author: Helene Ahme
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Yun Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 90
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To achieve net zero carbon emission required for a sustainable economy, global energy production requires a clean and reliable solution. Photovoltaic technology that directly converts sunlight into electricity has demonstrated its potential in contributing to a carbon free energy future. Among myriad solar technologies, photovoltaic cells based on organic semiconductors offer unique advantages of being light weight, flexible and low cost and have shown promising photovoltaic performance with efficiency climbing over 18%. In state-of-the-art organic solar cells, a mixture of polymer electron donor and electron acceptor molecules converts light energy to electrical energy. The rapid performance advancement from 11% to over 18% in recent years is largely achieved by the replacement of fullerene molecules with small molecules as electron acceptors, known as non-fullerene acceptors. These new materials not only unlock promising photovoltaic performance but more importantly pose new photophysical questions that challenge the research community’s original understanding of organic solar cells and suggest new design rules. Central to the photophysics of organic solar cells, as reviewed in Chapter 1, is the charge-transfer state formed between the electron donor molecular and the acceptor molecule. The work presented in this thesis focuses on understanding the properties of the charge-transfer state and its role in mediating energy loss in solar cells. Contrary to the traditional model in which significant driving energy is required to separate tightly bound electron-hole pair in the charge-transfer state, one surprising finding to the organic solar cell community is that the most efficient polymer/non-fullerene organic photovoltaics have negligible driving force for charge separation. Furthermore, compared to fullerene acceptors, non-fullerene acceptors have appreciable absorption, implying that charge generation via hole transfer from acceptor to donor could play an important role. In Chapter 2, via detailed time-resolved and steady state spectroscopic studies, we discover a slow yet efficient generation of the charge-transfer state and charge carriers via hole transfer using a model blend of polymer and non-fullerene acceptors. Our findings also allude to a new photophysical scheme in charge generation that was not observed in polymer/fullerene blends but important to efficient polymer/non-fullerene acceptor blends. Another remarkable property of many efficient polymer/non-fullerene blends is their high photoluminescence efficiency and consequently small non-radiative recombination loss, suggesting that "a great solar cell is also a great light emitting diode" also applies to organic solar cells and prompting research efforts on improving the luminescence efficiency of charge-transfer states. Based on Shockley-Queisser’s theoretical framework, an ideal solar cell should only suffer energy loss from radiative recombination as it is unavoidable, and that any non-radiative recombination is excess. In organic solar cells, however, due to molecular vibrations, non-radiative recombination loss contributes a significant amount to total energy loss. Current research efforts have shown that the non-radiative recombination loss follows an energy-gap law where higher gap materials have intrinsically lower loss. Moreover, photoluminescence yield of the charge-transfer state can be limited by that of the local exciton of the lower bandgap material when these states quantum mechanically mix. In Chapter 3, I combine spectroscopic methods and molecular dynamic calculations to examine in detail what molecular properties determine photoluminescence yield of the charge-transfer state and non-radiative recombination loss of the solar cell. After demonstrating an intrinsically emissive yet charge-generating small molecule blend, I show that due to wavefunction mixing between the charge-transfer state and the local exciton, both photoluminescence quantum yield and lifetime of the local exciton influences emission of the charge-transfer state. The latter is a new consideration for selecting materials for efficient organic photovoltaics and light emitting diodes. In Chapter 4, I propose and show current progress on a previously overlooked spectroscopy method directly detecting wavefunction mixing between the charge-transfer state and the local exciton of non-fullerene acceptor molecules. Our findings and proposal provide direction for molecular design and material selection to limit energy loss in organic solar cells.
Author: Riccardo Volpi
Publisher: Linköping University Electronic Press
ISBN: 9176856194
Category :
Languages : en
Pages : 66
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With the technological advancement of modern society, electronic devices are getting progressively more integrated in our everyday lives. Their continuouslygrowing presence is generating numerous concerns about costs, efficiency and the environmental impact of the electronic waste. In this context, organic electronics is finding its way through the market, allowing for potentially low-cost, light, flexible, transparent and environmentally friendly electronics. Despite the numerous successes of organic electronics, the functioning of several categories of organic devices still represents a technological challenge, due to problems like low efficiencies and stabilities (degradation over time). Organic devices are composed by one or more organic materials depending on the particular application. The conformation and electronic structure of the organic molecules as well as their supramolecular arrangement in the single phase or at the interface are known to strongly a affect the mobility and/or the efficiency of the device. While there is consensus on the fundamental physics of organic devices, we still lack a detailed comprehensive theory able to fully explain experimental data. In this thesis we focus on trying to expand our knowledge of charge transport in organic materials through theoretical modelling and simulation of organic electronic devices. While the methodology developed is generally valid for any organic device, we will particularly focus on the case represented by organic photovoltaics. The morphology of the system is obtained by molecular dynamics simulations. Marcus theory is used to calculate the hopping rate of the charge carriers and subsequently study the possibility of free charge carriers production in an organic solar cell. The theory is then compared both with Kinetic Monte Carlo simulations and with experiments to identify the main pitfalls of the actual theory and ways to improve it. The Marcus rate between two molecules depends on the molecular orbital energies, the transfer integral between the two molecules and the reorganization energy. The orbital energies and the transfer integrals between two neighbouring molecules are obtained through quantum mechanical calculations in vacuum. Electrostatic effects of the environment are included through atomic charges and atomic polarizabilities, producing a correction both to the orbital energy and to the reorganization energy. We have studied several systems in the single phase (polyphenylene vinylene, C60, PC61BM) and at the interface between two organic materials (anthracene/C60, TQ1/PC71BM). We show how a combination of different methodologies can be used to obtain a realistic ab-initio model of organic devices taking into account environmental effects. This allows us to obtain qualitative agreement with experimental data of mobility in the single phase and to determine whether or not two materials are suitable to be used together in an organic solar cell.
Author:
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ISBN:
Category :
Languages : en
Pages :
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Author: Yuxin Xia
Publisher: Linköping University Electronic Press
ISBN: 917685146X
Category :
Languages : en
Pages : 78
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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.
Author: Bo Wu
Publisher: Springer
ISBN: 9811020213
Category : Technology & Engineering
Languages : en
Pages : 114
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This book explores the incorporation of plasmonic nanostructures into organic solar cells, which offers an attractive light trapping and absorption approach to enhance power conversion efficiencies. The authors review the latest advances in the field and discuss the characterization of these hybrid devices using a combination of optical and electrical probes. Transient optical spectroscopies such as transient absorption and transient photoluminescence spectroscopy offer powerful tools for observing charge carrier dynamics in plasmonic organic solar cells. In conjunction with device electrical characterizations, they provide unambiguous proof of the effect of the plasmonic nanostructures on the solar cells’ performance. However, there have been a number of controversies over the effects of such integration – where both enhanced and decreased performance have been reported. Importantly, the new insights into the photophysics and charge dynamics of plasmonic organic solar cells that these spectroscopy methods yield could be used to resolve these controversies and provide clear guidelines for device design and fabrication.
Author: Flurin Eisner
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Author: Robert M. Metzger
Publisher: Springer Science & Business Media
ISBN: 3642272835
Category : Science
Languages : en
Pages : 317
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Charge Transport in Organic Semiconductors, by Heinz Bässler and Anna Köhler. Frontiers of Organic Conductors and Superconductors, by Gunzi Saito and Yukihiro Yoshida. Fullerenes, Carbon Nanotubes, and Graphene for Molecular Electronics, by Julio R. Pinzón, Adrián Villalta-Cerdas and Luis Echegoyen. Current Challenges in Organic Photovoltaic Solar Energy Conversion, by Cody W. Schlenker and Mark E. Thompson.- Molecular Monolayers as Semiconducting Channels in Field Effect Transistors, by Cherie R. Kagan. Issues and Challenges in Vapor-Deposited Top Metal Contacts for Molecule-Based Electronic Devices, by Masato M. Maitani and David L. Allara. Spin Polarized Electron Tunneling and Magnetoresistance in Molecular Junctions, by Greg Szulczewski.
Author: Jessica J. Benson
Publisher:
ISBN:
Category :
Languages : en
Pages :
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