On the Generation and Fate of Free Carriers in Non-fullerene Acceptor Organic Solar Cells PDF Download
Are you looking for read ebook online? Search for your book and save it on your Kindle device, PC, phones or tablets. Download On the Generation and Fate of Free Carriers in Non-fullerene Acceptor Organic Solar Cells PDF full book. Access full book title On the Generation and Fate of Free Carriers in Non-fullerene Acceptor Organic Solar Cells by Lorena Perdigón-Toro. Download full books in PDF and EPUB format.
Author: Lorena Perdigón-Toro
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Organic solar cells offer an efficient and cost-effective alternative for solar energy harvesting. This type of photovoltaic cell typically consists of a blend of two organic semiconductors, an electron donating polymer and a low molecular weight electron acceptor to create what is known as a bulk heterojunction (BHJ) morphology. Traditionally, fullerene-based acceptors have been used for this purpose. In recent years, the development of new acceptor molecules, so-called non-fullerene acceptors (NFA), has breathed new life into organic solar cell research, enabling record efficiencies close to 19%. Today, NFA-based solar cells are approaching their inorganic competitors in terms of photocurrent generation, but lag in terms of open circuit voltage (V_OC). Interestingly, the V_OC of these cells benefits from small offsets of orbital energies at the donor-NFA interface, although previous knowledge considered large energy offsets to be critical for efficient charge carrier generation. In addition, there are several other electronic and ...
Author: Lorena Perdigón-Toro
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Organic solar cells offer an efficient and cost-effective alternative for solar energy harvesting. This type of photovoltaic cell typically consists of a blend of two organic semiconductors, an electron donating polymer and a low molecular weight electron acceptor to create what is known as a bulk heterojunction (BHJ) morphology. Traditionally, fullerene-based acceptors have been used for this purpose. In recent years, the development of new acceptor molecules, so-called non-fullerene acceptors (NFA), has breathed new life into organic solar cell research, enabling record efficiencies close to 19%. Today, NFA-based solar cells are approaching their inorganic competitors in terms of photocurrent generation, but lag in terms of open circuit voltage (V_OC). Interestingly, the V_OC of these cells benefits from small offsets of orbital energies at the donor-NFA interface, although previous knowledge considered large energy offsets to be critical for efficient charge carrier generation. In addition, there are several other electronic and ...
Author: Yun Liu
Publisher:
ISBN:
Category :
Languages : en
Pages : 90
Get Book Here
Book Description
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: Fiona Jamieson
Publisher:
ISBN:
Category :
Languages : en
Pages :
Get Book Here
Book Description
Organic photovoltaic devices are receiving extensive interest, with device efficiencies now exceeding 8%. There is increasing evidence that the efficiency of dissociation of excitons (bound electron-hole pairs) into free charge carriers is a key factor determining device performance. Dissociation of these excitons occurs at the interface between donor and acceptor molecules in the photoactive layer of the device and is driven by a favourable difference in electronic energy levels between the two materials. Several factors can potentially determine the efficiency of this process, including interfacial energetic energies, molecular structure, film microstructure and device electric fields. This thesis employs optical spectroscopic techniques, including photoluminescence quenching and transient absorption spectroscopy to assay the efficiency of charge separation for a range of donor / acceptor blend films and devices, thereby providing new insights into the factors determining the efficiency of this process. The first results chapter focuses on the experimental technique, transient absorption spectroscopy, and how this can be employed to determine the yield of dissociated charges in donor / acceptor blend films. Three materials systems are studied, firstly looking at the effects of structure of the donor material, followed by a study into the effects of the temperature on charge generation and recombination. The following two chapters investigate the effects of film morphology on charge generation, specifically focusing upon the fullerene acceptor. Aggregation of phenyl-C61-butyric acid methyl ester (PCBM) is shown to be a key factor in the generation of free charges in the blend film, leading to proposal of a model regarding the role of this aggregation in charge generation. This study has then been extended by using additives to modify the concentration threshold for PCBM aggregation by preventing the intercalation of the PCBM between the polymer side chains, and hence inducing PCBM aggregation at a lower concentration. In the final chapter, the effects of an externally applied electric field on charge generation in devices have been studied. Such electric fields have been proposed to reduce geminate recombination losses, thereby increasing the dissociation of free charges, and thus leading to an increase in the device photocurrent. Polymer and small molecule blend systems have been studied and shown to exhibit different dependences of charge generation upon applied bias depending on the donor molecule and the morphology of the blend.
Author: Masahiro Hiramoto
Publisher: Springer Nature
ISBN: 981159113X
Category : Science
Languages : en
Pages : 271
Get Book Here
Book Description
This book focuses on the essential scientific ideas and breakthroughs in the last three decades for organic solar cells that have realized practical applications. The motivation for publishing this book is to explain how those essential ideas have arisen and to provide a foundation for future progress by target readers—students, novices in the field, and scientists with expertise. The main topics covered in the book include the fundamental principles and history of organic solar cells, blended junction, nanostructure control, photocurrent generation, photovoltage generation, doping, practical organic solar cells, and possible ideas for the future. The editors enthusiastically anticipate the vigorous development of the field of organic solar cells by young scientists of the next generation.
Author: Jona Kurpiers
Publisher:
ISBN:
Category :
Languages : en
Pages : 0
Get Book Here
Book Description
Organic semiconductors are a promising class of materials. Their special properties are the particularly good absorption, low weight and easy processing into thin films. Therefore, intense research has been devoted to the realization of thin film organic solar cells (OPVs). Because of the low dielectric constant of organic semiconductors, primary excitations (excitons) are strongly bound and a type II heterojunction needs to be introduced to split these excitations into free charges. Therefore, most organic solar cells consist of at least an electron donor and electron acceptor material. For such donor acceptor systems mainly three states are relevant; the photoexcited exciton on the donor or acceptor material, the charge transfer state at the donor-acceptor interface and the charge separated state of a free electron and hole. The interplay between these states significantly determines the efficiency of organic solar cells. Due to the high absorption and the low charge carrier mobilities, the active layers are usually thin but also,...
Author: Helene Ahme
Publisher:
ISBN: 9783839607794
Category :
Languages : en
Pages : 137
Get Book Here
Book Description
Author: Sarah Holliday
Publisher: Springer
ISBN: 3319770918
Category : Technology & Engineering
Languages : en
Pages : 119
Get Book Here
Book Description
This book reports on the design, synthesis and characterization of new small molecule electron acceptors for polymer solar cells. Starting with a detailed introduction to the science behind polymer solar cells, the author then goes on to review the challenges and advances made in developing non-fullerene acceptors so far. In the main body of the book, the author describes the design principles and synthetic strategy for a new family of acceptors, including detailed synthetic procedures and molecular modeling data used to predict physical properties. An indepth characterization of the photovoltaic performance, with transient absorption spectroscopy (TAS), photo-induced charge extraction, and grazing incidence X-ray diffraction (GIXRD) is also included, and the author uses this data to relate material properties and device performance. This book provides a useful overview for researchers beginning a project in this or related areas.
Author: Yongfang Li
Publisher: Springer
ISBN: 3319168622
Category : Technology & Engineering
Languages : en
Pages : 402
Get Book Here
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: Armantas Melianas
Publisher: Linköping University Electronic Press
ISBN: 9176855635
Category :
Languages : en
Pages : 101
Get Book Here
Book Description
Organic photovoltaic (OPV) devices based on semiconducting polymers and small molecules allow for a low cost alternative to inorganic solar cells. Recent developments show power conversion efficiencies as high as 10-12%, highlighting the potential of this technology. Nevertheless, further improvements are necessary to achieve commercialization. To a large extent the performance of these devices is dictated by their ability to extract the photo-generated charge, which is related to the charge carrier mobility. Various time-resolved and steady-state techniques are available to probe the charge carrier mobility in OPVs but often lead to different mobility values for one and the same system. Despite such conflicting observations it is generally assumed that charge transport in OPV devices can be described by well-defined charge carrier mobilities, typically obtained using a single steady-state technique. This thesis shows that the relevance of such well-defined mobilities for the charge separation and extraction processes is very limited. Although different transient techniques probe different time scales after photogeneration, they are mutually consistent as they probe the same physical mechanism governing charge motion – gradual thermalization of the photo-generated carriers in the disorder broadened density of states (DOS). The photo-generated carriers gradually lose their excess energy during transport to the extracting electrodes, but not immediately. Typically not all excess energy is dissipated as the photo-generated carriers tend to be extracted from the OPV device before reaching quasi-equilibrium. Carrier motion is governed by thermalization, leading to a time-dependent carrier mobility that is significantly higher than the steady-state mobility. This picture is confirmed by several transient techniques: Time-resolved Terahertz Spectroscopy (TRTS), Time-resolved Microwave Conductance (TRMC) combined with Transient Absorption (TA), electrical extraction of photo-induced charges (photo-CELIV). The connection between transient and steady-state mobility measurements (space-charge limited conductivity, SCLC) is described. Unification of transient opto-electric techniques to probe charge motion in OPVs is presented. Using transient experiments the distribution of extraction times of photo-generated charges in an operating OPV device has been determined and found to be strongly dispersive, spanning several decades in time. In view of the strong dispersion in extraction times the relevance of even a well-defined time-dependent mean mobility is limited. In OPVs a continuous ‘percolating’ donor network is often considered necessary for efficient hole extraction, whereas if the network is discontinuous, hole transport is thought to deteriorate significantly, limiting device performance. Here, it is shown that even highly diluted donor sites (5.7-10 %) in a buckminsterfullerene (C60) matrix enable reasonably efficient hole transport. Using transient measurements it is demonstrated that hole transport between isolated donor sites can occur by long-range hole tunneling (over distances of ~4 nm) through several C60 molecules – even a discontinuous donor network enables hole transport
Author: Bo Wu
Publisher: Springer
ISBN: 9811020213
Category : Technology & Engineering
Languages : en
Pages : 114
Get Book Here
Book Description
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.
