Download or read book On the Exciton Blocking Layer at the Interface Organic cathode in Planar Multiheterojunction Organic Solar Cells written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Non Equilibrium Charge Motion in Organic Solar Cells written by Armantas Melianas and published by Linköping University Electronic Press. This book was released on 2017-04-18 with total page 101 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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

Download or read book Exciton Behaviour at Organic Solar Cell Interfaces written by Olivia Dinica and published by . This book was released on 2015 with total page 244 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPVs) have emerged as a promising class of materials in the production of flexible and cheap solar cells. Polymer OPVs are typically composed of a blend of a semiconducting electron donating polymer with an electron accepting fullerene derivative. This blend leads to a high donor-acceptor interfacial surface area where excitons are split apart to create free charges. The generation of free charges after photo-excitation is a main factor influencing solar cell efficiency. However, the mechanisms of charge transfer and the competing process of charge recombination at the interface are not completely clear. The understanding of these processes is essential for the rational design of materials that can maximize photovoltaic conversion efficiencies. The focus of this dissertation is on the influence that electric fields and chemical structure have on exciton issociation and recombination at the interface of donor-acceptor materials. In particular, we use mixed classical dynamical simulations and electronic structure calculations to investigate several oligomer-fullerene systems. In order to study the potential energy surfaces guiding the dynamics of electron transfer, the nuclear and electron dynamics of large systems need to be simulated. To make these calculations computationally feasible, a mixed quantum classical molecular dynamics (MQCMD) approach was taken. This technique is based on the QCFF/PI formalism first described by Warshel and Karplus and was further developed by Lobaugh and Rossky for the simulation of betaine-30. This approach divides the conjugated system into a classical and a quantum subsystem. The quantum treatment is reserved for the [greek small letter pi] electronic system described by the Pariser-Parr-Pople (PPP) Hamiltonian. The classical potential describes a fully flexible molecular backbone and is modeled using an empirical molecular mechanics force field. In the first part of the dissertation we are examining the effect of an external electric field on charge transfer pathways and rates at sexithiophene/fullerene interfaces. In the second part, we develop a rigorous parametrization technique that allows us to model push-pull polymers. These polymers include PCDTBT and KP115 which have a more complex molecular structure than homo-polymers like the one considered in the first part. We use the QCFF/PI method as well as electronic structure calculations to investigate the influence of molecular structure and donor-acceptor orientation on charge transfer and recombination. The pathways linking exciton formation, charge transfer and thermal relaxation are explored, particularly in the context of dependence in the morphology of the donor molecules as well as the non-adiabatic coupling between excited states.

Download or read book Organic Solar Cells Towards High Efficiency written by Chuandao Charlie Wang and published by Open Dissertation Press. This book was released on 2017-01-26 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: This dissertation, "Organic Solar Cells Towards High Efficiency: Plasmonic Effects and Interface Engineering" by Chuandao, Charlie, Wang, 王传道, was obtained from The University of Hong Kong (Pokfulam, Hong Kong) and is being sold pursuant to Creative Commons: Attribution 3.0 Hong Kong License. The content of this dissertation has not been altered in any way. We have altered the formatting in order to facilitate the ease of printing and reading of the dissertation. All rights not granted by the above license are retained by the author. Abstract: Organic solar cells (OSCs) are promising candidates for solar light harvesting due to their standout advantages both in material properties and manufacturing process. During past decades, remarkable progress has been achieved. Efficiency for single-junction cells over 9% and tandem cells over 10% has been reported. For high performance OSCs towards commercialization, sufficient light absorption and high quality buffer layers are still two challenges, which are addressed in this thesis by investigating the plasmonic effects on OSCs and interface engineering. Here, the mechanisms of plasmonic effects on OSC are explored by incorporating metallic Au nanoparticles (NPs) in individual anode buffer layer and active layer, respectively, and finally in both layers simultaneously. When Au NPs are incorporated into the buffer layer, surface plasmonic resonance (SPR) induced absorption enhancement due to incorporation of Au NPs is evidenced theoretically and experimentally to be only minor contributor to the performance improvement. The increased interfacial contact area between the buffer layer and active layer, together with the reduced resistance of the buffer layer due to the embedded Au NPs, are revealed to benefit hole collection and thus are main contributors to the performance improvement. When Au NPs are embedded in the active layer, Au NPs induced SPR indeed contributes to enhanced light absorption. However, when large amount of Au NPs are incorporated, the negative effects of NPs on the electrical properties of OSCs can counter-diminish the optical enhancement from SPR, which limits the overall performance improvement. When Au NPs are embedded into both layers, both advantages of incorporating NPs in individual layers can be utilized together to achieve more pronounced improvement in photovoltaic performance; as a result, accumulated enhancements in device performance can be achieved. The results herein are applicable to other metallic NPs such as Ag NPs, Pt NPs, etc. The study herein has clarified the degree of contribution of SPR effects on OSCs and revealed the mechanisms behind. It has also highlighted the importance of considering both optical and electrical effects when employing metallic NPs as strategies to enhance the photovoltaic performance of OSCs. Consequently, the study contributes both physical understanding and technological development of applying metallic NPs on OSCs. Regarding interface engineering, we first propose a simple method to modify the substrate work function for efficient hole collection by using an ultra-thin ultraviolet-ozone treated Au. The method can be used in other situations such as modifying the work function of multilayer graphene as transparent electrode. Then we propose a general method to synthesize solution-processed transition metal oxides (TMOs). Besides high material quality, desirable electrical properties, and good stability, our method stands out particular in that the synthesized TMOs can be dispersed in water-free solvents and the TMO films require only low temperature treatment, which is very compatible with the organic electronics. Our method can also be used to synthesize other TMOs other than the demonstrated molybdenum oxide and vanadium oxide. The proposed method herein is applicable in semiconductor industry. DOI: 10.5353/th_b4832965 Subjects: Solar cells

Download or read book Organic Photovoltaic Cell Incorporating Electron Conducting Exciton Blocking Layers written by and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: The present disclosure relates to photosensitive optoelectronic devices including a compound blocking layer located between an acceptor material and a cathode, the compound blocking layer including: at least one electron conducting material, and at least one wide-gap electron conducting exciton blocking layer. For example, 3,4,9,10 perylenetetracarboxylic bisbenzimidazole (PTCBI) and 1,4,5,8-napthalene-tetracarboxylic-dianhydride (NTCDA) function as electron conducting and exciton blocking layers when interposed between the acceptor layer and cathode. Both materials serve as efficient electron conductors, leading to a fill factor as high as 0.70. By using an NTCDA/PTCBI compound blocking layer structure increased power conversion efficiency is achieved, compared to an analogous device using a conventional blocking layers shown to conduct electrons via damage-induced midgap states.

Download or read book Interfacial Composition of the Oxide Donor Interface Probing Morphology and Charge Injection Extraction in Organic Photovoltaics written by Jeremy L. Gantz and published by . This book was released on 2014 with total page 259 pages. Available in PDF, EPUB and Kindle. Book excerpt: The role of the transparent conducting oxide (TCO) and the organic donor material interface in small molecule planar heterojunction (PHJ) and bulk heterojunction (BHJ) solar cells (OPV) was investigated and are presented as three projects: 1) the influence of the electrode surface composition and energetics on small molecule organic solar cell performance: Polar vs. non-polar donors on indium tin oxide (ITO) contacts, 2) the study of the oxide donor contact electrical properties utilizing metal-insulator-semiconductor capacitor (MIS-C) devices to probe the dark current contributions of a single interface in organic solar cells, 3) the role of the hole transport layer type and morphology in small molecule BHJ solar cells: correlating trap state density with OPV performance and d) using fluorinated subphthalocyanines as multifunctional materials in OPVs. Organic semiconductor material properties are varied and the role of each class of material functions differently when incorporated into an organic photovoltaic. Polar donor materials such as indium (III) phthalocyanine chloride (ClInPc) adopt different molecular configurations on high work function ITO electrodes as opposed to low work function electrodes which sets itself apart from non-polar electron donating materials. We find that not only does molecular orientation effect the optical properties of these thin films, but the charge transfer properties that occur at the oxide/donor interface influence the overall device performance in OPVs and can be probed using MIS-C devices and high resolution photoemission spectroscopy. We also investigate how the morphology of the hole selective interlayer in BHJ OPVs influences the resulting trap state density and OPV performance.

Download or read book Interface Passivation for Improving Performance and Stability in Organic Solar Cells written by Zhuo Xu and published by . This book was released on 2024* with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the past 30 years, the power conversion efficiency (PCE) of Organic solar cells (OSCs) has significantly improved from 1% to over 19%, positioning them as one of the promising technologies for addressing the 21st-century energy crisis. This dissertation investigates three approaches to improving the efficiency and stability of OSCs. The first part explores the blending of inorganic and organic materials to leverage their respective advantages and passivity their drawbacks, resulting in enhanced device efficiency. However, due to the intrinsic instability of the PM6:Y6 system. A widely used sunscreen material was introduced between the electron transport layer (ETL) and the active layer to block UV radiation from damaging the active layer, thereby improving device stability. This sunscreen material not only enhanced exciton extraction efficiency, increasing PCE, but also provided significant UV stability under high UV content simulated sunlight. ZnO, a popular ETL material in inverted solar cells, is not without its limitations. Post-deposition, the surface of ZnO often exhibits residual -OH groups, which have been shown to generate radicals under illumination, attacking the end groups of acceptor materials. To address this, the study introduced a self-assembled monolayer (SAM) on the ZnO surface to passivate these effects. This modification significantly improved both the efficiency and stability of the OSCs. Moreover, since these organic acids can function as both hole and electron transport layers, their application on both sides of the active layer further enhanced the device lifetime without substantial loss in PCE. In summary, this thesis demonstrates three straightforward and effective strategies for modifying charge transport materials in OSCs, addressing various challenges and enhancing both efficiency and stability. These approaches have the potential to contribute significantly to the future application of high-efficiency, stable solar cell devices.

Download or read book Interface Engineering and Electrode Engineering for Organic Solar Cells written by Dazheng Chen and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Interface engineering and electrode engineering play important roles in the performance improvement for organic solar cells (OSCs). We here would investigate the effect of various cathode modifying layers and ITO-free electrodes on the device performance. First, for inverted organic solar cells (IOSCs) with a poly (3-hexylthiophene-2,5-diyl):[6,6]-phenyl C61 butyric acid methyl ester blend, an aqueous solution method using low temperatures is adopted to deposit a ZnO interlayer in IOSCs. When the ZnO annealing temperature is above 80°C, the corresponding IOSCs show senior PCEs over 3.5%. Meanwhile the flexible devices based on poly(ethylene terephthalate) substrate display a PCE of 3.26% and good flexibility. Second, the performance of IOSCs based on AZO cathode and Ca modifier are studied. The resulted IOSCs with an ultrathin Ca modifier (~1 nm) could achieve a senior PCE above 3%, and highly efficient electron transport at AZO/Ca/organic interface, which obviously weakens the light soaking issue. Third, by introducing a 2 nm MoO3 interlayer for Ag anode deposition, the obtained OSCs show an improved PCE of 2.71%, and the flexible device also achieves a comparable PCE of 2.50%. All these investigations may be instructive for further improvement of device performance and the possible commercialization in the future.

Download or read book Organic Solar Cells Performances Improvement Induced by Interface Buffer Layers written by J. C. Bernède and published by . This book was released on 2010 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic Solar Cells Performances Improvement Induced by Interface Buffer Layers.

Download or read book Organic Solar Cells written by Modest Voronov and published by Nova Science Publishers. This book was released on 2017 with total page 127 pages. Available in PDF, EPUB and Kindle. Book excerpt: The last two decades have seen unprecedented research progress made in the fabrication and testing of organic solar cell (OSC) devices due to, among other things, rapid growth of interest in the development of organic materials for photovoltaic applications, the ease of processing, and the prospect of achieving high power conversion efficiency (PCE) cost effectively. The effects of impurity doping at the ppm level in photovoltaic organic semiconductors, including: (i) "Seven-nines" purification of organic semiconductors, (ii) pn-control of single and co-deposited organic semiconductors by impurity doping, (iii) ionization sensitization of doping showing the doping efficiency of 100%, (iv) ppm-doping effects in the simplest n+p-homojunction organic photovoltaic cells, and (v) the Hall effect of bulk-doped organic single crystals, are discussed in Chapter One. In Chapter Two the fabrication and characterization of perovskite-type solar cells are reviewed and summarized such as CH3NH3PbI3, [HC(NH2)2]PbI3, and CsSnI3, which are expected for solar cell materials. Chapter Three proposes an experimental method to tailor SDE and optimize the power conversion efficiency (PCE), based on the electrical transport curve. Chapter Four provides a brief history of organic photovoltaic cell devices, factors limiting stability and power conversion efficiency, fundamental parameters that have been reported to improve the general performance of the devices, and recent developments in organic solar cell devices.

Download or read book Schottky Behavior of Organic Solar Cells with Different Cathode Deposition Methods written by Laxman Anishetty and published by . This book was released on 2011 with total page 66 pages. Available in PDF, EPUB and Kindle. Book excerpt: During the last decade, organic photovoltaic research has attracted attention and power conversion efficiencies have shown strong growth. This growth has attracted economic and scientific interest towards organic solar cell. This attention was possible due to the introduction of new polymer materials, inorganic molecules, sophisticated methods of fabrication, and improved material technologies. Bulk-Hetero Junction solar cells achieved 7 % efficiency with the introduction of inorganic small molecules in organic polymers. Organic solar cells of 12% efficiency are targeted. However, the degradation of organic semiconductors due to the environment and the effect of cathode deposition make the organic solar cells inferior to silicon solar cells. In this thesis, the effect of cathode deposition with various deposition methods was studied. The Dark Capacitance-Voltage characteristics and Capacitance-Frequency characteristics Of MEH PPV (Poly (p-phenylene vinylene) (PPV)) Solar cell with sputtering and thermal evaporation of the aluminum cathode are reported here. Capacitances are measured at different temperatures using cryogenic testing. Interface state densities and their time constants are calculated and analyzed. The variance of depletion width, interface state densities and time constants with two different processes is discussed here. The observations indicated that rf sputtering deposition of cathode is introduces greater interface densities compared to thermal evaporation devices.

Download or read book Organic Solar Cells Towards High Efficiency written by Chuandao Wang (Charlie) and published by . This book was released on 2012 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book P3HT PCBM based Organic Solar Cells written by Burak Yahya Kadem and published by . This book was released on 2017 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Organic Solar Cells Towards High Efficiency written by Chuandao Wang (Charlie) and published by . This book was released on 2012 with total page 330 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Correlating High Power Conversion Efficiency of PTB7 written by and published by . This book was released on 2015 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Advances in materials design and device engineering led to inverted organic solar cells (i-OSCs) with superior power conversion efficiencies (PCEs) to their conventional counterparts, in addition to the well-known better ambient stability. Despite the significant progress, however, it has so far been unclear how the morphologies of the photoactive layer and its interface with the cathode modifying layer impact device performance. Here, we report an in-depth morphology study of the i-OSC active and cathode modifying layers, employing a model system with the well-established bulk-heterojunction, PTB7:PC71BM as the active layer and poly-[(9,9-bis(3 -(N, N-dimethylamino)propyl)-2,7-fluorene)-alt-2,7-(9,9-dioctylfluorene)] (PFN) as the cathode surface modifying layer. We have also identified the role of a processing additive, 1,8-diiodooctane (DIO), used in the spin-casting of the active layer to increase PCE. Using a variety of characterization techniques, we demonstrate that the high PCEs of i-OSCs are due to the smearing (diffusion) of electron-accepting PC71BM into the PFN layer, resulting in improved electron transport. The PC71BM diffusion occurs after spin-casting the active layer onto the PFN layer, when residual solvent molecules act as a plasticizer. The DIO additive, with a higher boiling point than the host solvent, has a longer residence time in the spin-cast active layer, resulting in more PC71BM smearing and therefore more efficient electron transport. This work provides important insight and guidance to further enhancement of i-OSC performance by materials and interface engineering.

Download or read book Understanding Exciton Diffusion in Organic Solar Cells written by Amy Illingworth and published by . This book was released on 2012 with total page 174 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Transient Optical Studies of Exciton Dynamics in Organic Solar Cells written by Luke X. Reynolds and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: There is increasing evidence that the initially generated excited state species in bulk heterojunction solar cell photoactive layers are critical to device performance. At present however, an understanding of the nature and dynamics of such excited states still remains limited. This thesis presents a study of the ultrafast exciton dynamics in bulk heterojunction organic and hybrid organic-inorganic solar cells. Fluorescence upconversion is used to elucidate the dynamics of such transient species allowing internal properties of the blend systems to be probed including changes in film morphology and ultrafast energy loss mechanisms. An understanding of such processes is an important step forward in the evolution of molecular semiconductor based solar cells. The first chapter focuses on the main experimental technique, fluorescence upconversion, and how this can be employed to study excited states. In particular, this section addresses one of the main unanswered questions in the field and attempts to correlate the exciton dynamics with the structure of the common photoactive polymer poly(3-hexylthiophene) (P3HT). Three structural variations of P3HT are studied and their exciton dynamics associated with differing internal processes occurring within the polymers. These include self localisation, and different types of long-range energy transfer mechanisms. The following two chapters build upon the knowledge of exciton dynamics obtained from the first chapter. First, a study is made of amorphous polymers with different acceptors, all based on phenyl-C61-butyric acid methyl ester (PCBM). The distinct interactions of the PCBM-type molecules with the polymer results in different electron transfer dynamics, from which the exciton diffusion length of the polymer in real bulk heterojunction blends is extracted using a simple model. Second, the ultrafast excited state dynamics of a crystalline polymer with the same PCBM-type acceptors is studied. Correlation of these dynamics with thermal analysis of the blend films allows the morphology of the films to be extracted and allows two different mechanisms of microstructure development to be identified. In the final chapter, the effect of acceptor aggregation on exciton dynamics and charge generation yields in hybrid organic-inorganic blend films has been studied. Such aggregation has been shown to be essential for efficient charge generation in all-organic solar cells but has often been assumed to be less important in such inorganic hybrids. More aggregated acceptor nanoparticles are shown to not only result in greater than expected exciton quenching but are also shown to result in a greater yield of long-lived charges. This study is extended to show that in-situ grown inorganic nanoparticles exhibit superior performance to standard pre-synthesised inorganics.