Exciton Generation And Dissociation Mechanisms In Organic Bulk Heterojunction Solar Cell Materials
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| Author | : Hemant M. Shah |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2012 |
| Genre | : Exciton theory |
| ISBN | : |
Characterization of the optical and electrical properties of organic solar cell materials is of prime importance to organic solar cell design. This thesis describes the use of capacitive photocurrent measurements to study the exciton generation and dissociation mechanisms of organic solar cell materials. The emphasis is on the study of the methanofullerene derivatives (e.g., PCBM) which act as the electron acceptor material. This is because much work has already been done studying electron donating polymers used in organic solar cells (in an effort to enhance their absorbance coefficient), but less information is available on the acceptor material. In the blend films of MDMO-PPV: PCBM, the charge generation rate in PCBM was discovered to be much higher than would be expected from the absorbance cross-section. This observation led to design of a photovoltage bleaching experiment to examine the charge generation mechanism. Here the effect of illumination by a tunable light source on the open circuit photovoltage of a MDMO-PPV: PCBM bulk heterojunction solar cell was measured. Illumination of light at the PCBM ground state singlet exciton causes a sharp decrease in the photovoltage, while illumination at the ground state MDMO-PPV exciton shows no change. A direct pathway of recombination of above gap generated charge carriers was identified. Photovoltage bleaching results suggests that excitation at the PCBM ground singlet state exciton increases the recombination rate of higher energy excitations, either by acting as a recombination center or by forcing higher energy carriers into short lived states that recombine before reaching the contacts. The fact that the photovoltage bleaching correlates with the ground state PCBM singlet exciton suggests that charge dissociation from PCBM preferentially generates long-lived localized states. Capacitive photocurrent measurements were then performed on isolated methanofullerene derivatives, with the polymer donor material absent. Several low energy transitions were resolved in the optical spectroscopy of methanofullerene derivatives. These low energy states lay below the optical energy band-gap of these materials, so that their presence was unexpected. It was determined that the low energy states overlapped with the plasmon state of the highly conducting substrates (Indium Tin Oxide) which were in close proximity with the PCBM. Plasmon states in ITO have been observed previously, but the results presented in this thesis are unique in that this is the first evidence of charge transfer from the plasmon state of ITO to a high electron affinity fullerene derivative. The results show the evidence of charge transfer from PCBM to ITO over a broad wavelength range of 400 - 2400 nm (3 eV - 0.5 eV). Few materials have been observed to have absorbance and charge transfer over such a large range of energies in the infra-red regime. These results open a new direction for development of organic solar cell design with higher power conversion efficiencies.
| Author | : George Frederick Burkhard |
| Publisher | : Stanford University |
| Total Pages | : 113 |
| Release | : 2011 |
| Genre | : |
| ISBN | : |
Finding alternatives to fossil fuel energy sources is necessary to stem global warming, to provide economic and political independence, and to keep up with increasing energy demand. Because of their low cost, flexibility, and because the material resources needed to make them are abundant, organic polymer solar cells are an attractive alternative to conventional solar technology. Organic solar technology has been developing rapidly; however, with the best power conversion efficiencies at ~8%, much improvement is needed before it can be competitive with established solar technologies. Poly-3-hexylthiophene:[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cells are the most studied type of organic solar cell. Nevertheless, their loss mechanisms are still not fully understood. In this work, we study excitonic losses in the PCBM phase of the blend. We develop a way to accurately measure internal quantum efficiencies (IQEs) and use this technique to characterize P3HT:PCBM devices. We observe spectral dependence of the IQE and conclude that a majority of excitons generated in the PCBM are lost to Auger recombination with polarons that are trapped in that phase. We also provide evidence that this process may happen in other materials and may be a critical factor in limiting exciton diffusion in organic semiconductors.
| Author | : Wallace C.H. Choy |
| Publisher | : Springer Science & Business Media |
| Total Pages | : 268 |
| Release | : 2012-11-19 |
| Genre | : Technology & Engineering |
| ISBN | : 1447148231 |
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.
| Author | : Tetsuo Soga |
| Publisher | : Elsevier |
| Total Pages | : 616 |
| Release | : 2006-12-14 |
| Genre | : Science |
| ISBN | : 0080468306 |
Nanostructured Materials for Solar Energy Conversion covers a wide variety of materials and device types from inorganic materials to organic materials. This book deals with basic semiconductor physics, modelling of nanostructured solar cell, nanostructure of conventional solar cells such as silicon, CIS and CdTe, dye-sensitized solar cell, organic solar cell, photosynthetic materials, fullerene, extremely thin absorber (ETA) solar cell, quantum structured solar cell, intermediate band solar cell, carbon nanotube, etc. including basic principle and the latest results. There are many books written on conventional p-n junction solar cells, but few books focus on new concepts in this area. * Focuses on the use of nanostructured materials for solar energy* Looks at a wide variety of materials and device types* Covers both organic and inorganic materials
| Author | : Oksana Ostroverkhova |
| Publisher | : Woodhead Publishing |
| Total Pages | : 914 |
| Release | : 2018-11-30 |
| Genre | : Technology & Engineering |
| ISBN | : 0081022859 |
Handbook of Organic Materials for Electronic and Photonic Devices, Second Edition, provides an overview of the materials, mechanisms, characterization techniques, structure-property relationships, and most promising applications of organic materials. This new release includes new content on emerging organic materials, expanded content on the basic physics behind electronic properties, and new chapters on organic photonics. As advances in organic materials design, fabrication, and processing that enabled charge unprecedented carrier mobilities and power conversion efficiencies have made dramatic advances since the first edition, this latest release presents a necessary understanding of the underlying physics that enabled novel material design and improved organic device design. Provides a comprehensive overview of the materials, mechanisms, characterization techniques, and structure property relationships of organic electronic and photonic materials Reviews key applications, including organic solar cells, light-emitting diodes electrochemical cells, sensors, transistors, bioelectronics, and memory devices New content to reflect latest advances in our understanding of underlying physics to enable material design and device fabrication
| Author | : Buddika KA. Abeyweera |
| Publisher | : |
| Total Pages | : 118 |
| Release | : 2013 |
| Genre | : Conjugated polymers |
| ISBN | : |
Charge transfer and charge extraction mechanisms are two prevalent issues in the growing field of organic solar cells. Due to their complexity in nature, new methods need to be involved in addressing the fundamental properties associated with organic polymer solar cells. This dissertation has focused on developing a new method to estimate the charge collection lengths and surface recombination lengths of organic polymer solar cells. Photocurrent spectra have been analyzed systematically to observe the dependence on thickness of the active material. A red shift of the peak of the normalized photocurrent with respect to the device thickness has been further analyzed for two major material systems used in organic polymer solar cells, namely MDMO-PPV: PCBM and P3HT: PCBM. A theoretical model that measures the charge extraction of bulk hetero junction solar cell structures has been used taking into account of three main parameters including charge carrier collection length, absorption variation and surface recombination. This model has led to estimate two important parameters associated with charge transfer, recombination and extraction of organic solar cells which will provide opportunities for improvements in the performance of organic electronic devices. Key results are summarized as follows. A complete analysis of photocurrent spectra has been done to see its variation with active material thickness of well-known two material systems of bulk heterojunction organic solar cells. Results of these preliminary measurements suggest that peak of the photocurrent for both systems red shift with increasing thickness. Charge extraction model is introduced to explain the initial red shift of the photocurrent. This model fits well with the experimental results. Further analysis of the model suggests that the charge collection lengths can be estimated for organic polymer structures. Theoretical model gives higher collections lengths for MDMO-PPV solar cells while a lower collection length for P3HT solar cells. This model also has the capability to estimate the surface recombination length of organic bulk heterojunction solar cells. Different interfacial layers have been used to fit to the model calculation. These results suggest that the least surface recombination lengths were achieved with solar cells of PEDOT-PSS. This method can be used to optimize the interfacial layers to improve the efficiency in organic solar cells. AC photocurrent measurements have been carried out to observe the frequency dependence of organic solar cells. Main results show that increasing response time from the light source increases the performance of the solar cells. Further analysis of these results suggests that thicker devices of organic polymer solar cells can be applied with longer response time light sources. Degradation of organic polymer solar cells over a period of several days has been carried out to observe the stability of solar cells with device thickness. Results suggest that the degradation occurs regardless of device thickness of the active material. A new probing technique called capacitive photocurrent spectroscopy (CPS) has been carried out with P3HT solar cells to observe the charge dissociation efficiency. The CPS measurements suggest that sub band gap states have higher dissociation efficiencies that may not contribute to overall photocurrent of the solar cells.
| Author | : George Frederick Burkhard |
| Publisher | : |
| Total Pages | : |
| Release | : 2011 |
| Genre | : |
| ISBN | : |
Finding alternatives to fossil fuel energy sources is necessary to stem global warming, to provide economic and political independence, and to keep up with increasing energy demand. Because of their low cost, flexibility, and because the material resources needed to make them are abundant, organic polymer solar cells are an attractive alternative to conventional solar technology. Organic solar technology has been developing rapidly; however, with the best power conversion efficiencies at ~8%, much improvement is needed before it can be competitive with established solar technologies. Poly-3-hexylthiophene:[6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PCBM) solar cells are the most studied type of organic solar cell. Nevertheless, their loss mechanisms are still not fully understood. In this work, we study excitonic losses in the PCBM phase of the blend. We develop a way to accurately measure internal quantum efficiencies (IQEs) and use this technique to characterize P3HT:PCBM devices. We observe spectral dependence of the IQE and conclude that a majority of excitons generated in the PCBM are lost to Auger recombination with polarons that are trapped in that phase. We also provide evidence that this process may happen in other materials and may be a critical factor in limiting exciton diffusion in organic semiconductors.
| Author | : Dibya Prakash Rai |
| Publisher | : Bentham Science Publishers |
| Total Pages | : 299 |
| Release | : 2022-09-30 |
| Genre | : Science |
| ISBN | : 9815049976 |
The discovery of new materials and the manipulation of their exotic properties for device fabrication is crucial for advancing technology. Nanoscience, and the creation of nanomaterials have taken materials science and electronics to new heights for the benefit of mankind.Advanced Materials and Nanosystems: Theory and Experiment covers several topics of nanoscience research. The compiled chapters aim to update students, teachers, and scientists by highlighting modern developments in materials science theory and experiments. The significant role of new materials in future technology is also demonstrated. The book serves as a reference for curriculum development in technical institutions and research programs in the field of physics, chemistry and applied areas of science like materials science, chemical engineering and electronics. This part covers 12 topics in these areas: - Recent advancements in nanotechnology: a human health Perspective. - An exploratory study on characteristics of SWIRL of AlGaAs/GaAs in advanced bio based nanotechnological systems. - Electronic structure of the half-Heusler ScAuSn, LuAuSn and their superlattice. - Recent trends in nanosystems. - Improvement of performance of single and multicrystalline silicon solar cell using low-temperature surface passivation layer and antireflection coating. - Advanced materials and nanosystems. - Effect of nanostructure-materials on optical properties of some rare earth ions doped in silica matrix. - Nd2Fe14B and SmCO5: a permanent magnet for magnetic data storage and data transfer technology. - Visible light induced photocatalytic activity of MWCNTS decorated sulfide based nano photocatalysts. - Organic solar cells. - Neodymium doped lithium borosilicate glasses. - Comprehensive quantum mechanical study of structural features, reactivity, molecular properties and wave function-based characteristics of capmatinib.
| Author | : Adrian Velazquez Osorio |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2021 |
| Genre | : Organic photovoltaic cells |
| ISBN | : |
The world's growing energy consumption and increasingly visible effects of climate change originated in continued dependence on fossil fuels has strengthened the push to develop cleaner and renewable sources of energy. Solar photovoltaic cells are at the forefront of an ongoing energy transition and a new generation of solar technology based on organic semiconductor materials - organic solar cells - is capturing the attention of researchers because of their unique properties. Organic solar cells are photovoltaic devices that convert radiation into electricity using carbon-abundant materials. They can be manufactured to be flexible, semi-transparent, lightweight, and inexpensively produced on a large scale by roll-to-roll processes. In this thesis work, a brief introduction on possible applications and operating principles of organic solar cells provides the background to the area. Chapter 1 describes the heart of the organic solar cell, the photoactive layer known as the bulk heterojunction, and the basics of the mechanisms behind photon harvesting via exciton generation, dissociation, and collection. The main photovoltaic metrics used to characterize these devices are also discussed. Chapter 2 provides an overview of approaches used in the design of donor and acceptor materials and mentions how computer-driven optimization is emerging as an experimental paradigm to navigate the vast variable space involved in making the bulk heterojunction. The core section of this chapter focuses on approaches to improve solution processability of PM6:BTP-BO-4Cl OPV cells. Special emphasis is given to the application of methanol-based solvent annealing treatments and their role in inducing film dewetting of the PEDOT:PSS layer. Chapter 3 continues this focus on optimization of the bulk heterojunction by discussing the application of microwave annealing of a ZR1:BTP-BO-4Cl composition. A brief critical overview on the application of microwave annealing to increase photovoltaic performance of organic solar cells is presented. Later, evaluation of different microwave annealing setups is examined.
| Author | : Md. Akhtaruzzaman |
| Publisher | : Academic Press |
| Total Pages | : 420 |
| Release | : 2021-11-18 |
| Genre | : Science |
| ISBN | : 0323858074 |
Comprehensive Guide on Organic and Inorganic Solar Cells: Fundamental Concepts to Fabrication Methods is a one-stop, authoritative resource on all types of inorganic, organic and hybrid solar cells, including their theoretical background and the practical knowledge required for fabrication. With chapters rigorously dedicated to a particular type of solar cell, each subchapter takes a detailed look at synthesis recipes, deposition techniques, materials properties and their influence on solar cell performance, including advanced characterization methods with materials selection and experimental techniques. By addressing the evolution of solar cell technologies, second generation thin-film photovoltaics, organic solar cells, and finally, the latest hybrid organic-inorganic approaches, this book benefits students and researchers in solar cell technology to understand the similarities, differences, benefits and challenges of each device. Introduces the basic concepts of different photovoltaic cells to audiences from a wide variety of academic backgrounds Consists of working principles of a particular category of solar technology followed by dissection of every component within the architecture Crucial experimental procedures for the fabrication of solar cell devices are introduced, aiding picture practical application of the technology
