Download or read book Probing Exciton and Charge Dynamics in Organic Thin Films and Photovoltaics with Nonlinear Spectroscopy written by Thomas James McDonough and published by . This book was released on 2017 with total page 109 pages. Available in PDF, EPUB and Kindle. Book excerpt: Emerging organic solar cell technologies offer unique advantages over silicon solar cells, such as solution processability and the use of flexible substrates, but the efficiencies of these devices do not yet match the efficiency of silicon. Ultrafast nonlinear spectroscopies can probe the fates of photoexcited species on timescales in which these species are lost to channels that do not result in electric current. In the first study, I compare the ultrafast dynamics of singlet fission and charge generation in pentacene films grown on glass and graphene. The molecular orientation is different on the two substrates: the long axis of the pentacene molecules are "standing-up" (normal to the surface) on glass and "lying-down" (parallel to the surface) on graphene. By studying the fluence and polarization dependence of the transient absorption of pentacene on these two substrates, I am able to clarify previous spectral assignments. I identify a broad, isotropic absorption at 853 nm as due in significant part to hole absorption, in contrast to this feature's typical assignment to T1-T2 absorption. At high fluence, additional peaks at 614 and 688 (on glass) nm appear, whose kinetics and anisotropies are not explained by heating, which I assign to charge generation. In the second study, I utilize two-dimensional white-light spectroscopy to study the morphology dependence of exciton diffusion in semiconducting carbon nanotubes. I analyze the spectral diffusion of the S1-S1 2D-WL lineshape via the center line slope method to separate the homogeneous and inhomogeneous contributions to the lineshape in each sample. I determine a morphology independent homogeneous linewidth of ~10 meV, but I find that the inhomogeneous linewidth is sensitive to the particular sample environment. I model our experimental spectra with kinetic Monte Carlo simulations of exciton diffusion in a 1D potential. I also present preliminary bias-dependent transient absorption and 2D-WL measurements of carbon nanotube solar cell devices. I observe increasing positive trion absorption with increasing forward bias. The kinetics in the device are much different than the kinetics in the thin film, and there is an interesting change in kinetics with bias voltage that requires further investigation.
Download or read book Exciton Dynamics in Conjugated Polymer Photovoltaics written by Stephanie V. Chasteen and published by . This book was released on 2005 with total page 558 pages. Available in PDF, EPUB and Kindle. Book excerpt:
Download or read book Solar Fuels written by Theodore Goodson, III and published by CRC Press. This book was released on 2017-04-28 with total page 154 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written for use as a text and reference for those interested in how new materials may be used to capture, store, and use solar energy for alternative energy resources in everyday life, Solar Fuels: Materials, Physics, and Applications discusses the fundamentals of new materials and the physical processes involved in their mechanisms and design. This book offers clear examples of current state-of-the-art organic and inorganic solar cell materials and devices used in the field, and includes experiments testing solar capability along with standardized examples. Last, but not least, it also gives a clear outline of the challenges that need to be addressed moving forward.
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.
Download or read book Solar Fuels written by Theodore Goodson, III and published by CRC Press. This book was released on 2017-04-28 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Written for use as a text and reference for those interested in how new materials may be used to capture, store, and use solar energy for alternative energy resources in everyday life, Solar Fuels: Materials, Physics, and Applications discusses the fundamentals of new materials and the physical processes involved in their mechanisms and design. This book offers clear examples of current state-of-the-art organic and inorganic solar cell materials and devices used in the field, and includes experiments testing solar capability along with standardized examples. Last, but not least, it also gives a clear outline of the challenges that need to be addressed moving forward.
Download or read book Elementary Processes in Organic Photovoltaics written by Karl Leo and published by Springer. This book was released on 2016-12-20 with total page 423 pages. Available in PDF, EPUB and Kindle. Book excerpt: This volume presents the results of a multi-year research programme funded by the Deutsche Forschungsgemeinschaft (German Research Council), which explains how organic solar cells work. In this new promising photovoltaic technology, carbon-based materials are deposited by low-cost methods onto flexible substrates, thus allowing devices which open completely new applications like transparent coatings for building, solar cells integrated into clothing or packages, and many more. The investigation of organic solar cells is an interdisciplinary topic, covering physics, chemistry and engineering. The different chapters address topics ranging from the synthesis of new organic materials, to the characterization of the elementary processes such as exciton transport and separation, and the principles of highly efficient device design. /div
Download or read book Charge transfer and Other Excitonic State in Conjugated Polymer written by Dhanashree Moghe and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Over the last few decades there has been tremendous progress in organic photovoltaics (OPVs), with efficiencies reaching over 10%. Still, many factors including the origin and the dynamics of charge carrier involved are debatable. New and sensitive techniques are constantly being devised to identify the origin of free charges. At the same time, a lot of research has also been devoted to synthesize low bandgap material such that its absorption spectra overlap with that of the solar spectrum. The most important hindrance in organic semiconductors is the formation of bound electron-hole (exciton) charge pair upon photoexcitation. Additional energy is required to dissociate the bound pair to generate free charges for photovoltaic application. The most popular and efficient way to dissociate excitons is to fabricate a bulk heterojunction solar cell, which comprises of a blend of at least two polymers: one donor and the other acceptor. It is very well established that the presence of fullerene (acceptor) helps in transfer of the negative charges from the donor polymer to fullerene, making the exciton slightly less bound. The nanometer scale islands further help in migration of charges. A crucial aspect of our studies has been evaluating the role of various excitonic states such as charge-transfer and triplet excitonic states in device efficiencies. The focus of this work was on diketopyrrolopyrrole (DPP)- based donor-acceptor (D-A) type conjugated copolymers which have low bandgap energies and have been known to show high efficiency in organic photovoltaics. These copolymers have D-A unit present in the same chain, which lowers the optical bandgap of the material. Variation of either the donor or the acceptor fraction offers an option to tune the optical bandgap by using the same D-A chromophores. The D-A configuration also results in the separation of positive and negative charges within the same polymeric chain, which is the intramolecular charge-transfer excitonic state. We analyze the intramolecular charge-transfer state using bias dependent absorption studies, which allowed us to estimate the binding energy of intramolecular exciton. Later, we performed density functional theory (DFT) and time dependent DFT calculations to identify the origin of the intramolecular exciton absorption. Taking the copolymers as donor (and fullerene as acceptor) in an organic photovoltaic device, we probe the (intermolecular) charge-transfer states formed at the copolymer/fullerene interface . We utilize monochromatic photocurrent method and a highly sensitive (and fast) Fourier transform photocurrent spectroscopy technique to probe the intermolecular charge-transfer states in the device. Our analyses show that the optical bandgap difference between the copolymers and fullerene plays a pivotal role in stabilization /destabilization of charge - transfer states in copolymer-fullerene systems. The triplet excitons are also known to play an important role in OPV efficiency. We probe the diffusion length of triplet exciton in ladder-type polymers by devising a simple, yet efficient method using optical modulation spectroscopy (photoinduced absorption spectroscopy). The diffusion length of triplet excitons is estimated to be almost three orders of magnitude more than the singlet excitons . Further, by implementing a 1D random-walk model to the photoinduced absorption data, we estimate diffusivities of the triplet exciton in our sample.
Download or read book Nonlinear Optical and Charge Distribution Studies Probing Electric Field Effects in Polymer Thin Films for Second Order Nonlinear Optical Applications written by and published by . This book was released on 1996 with total page 35 pages. Available in PDF, EPUB and Kindle. Book excerpt: The goals of the research are two fold; First, determine the internal electric field effects from studies of charge magnitude, symmetry and distribution in dye-doped polymer systems. Second, a better understanding of the electric field effects on the chromophore mobility during and after poling. To this end, several techniques are being employed. Electrochromism technique is being used to determine the charge magnitude inside film samples. The films are 4-dimethylamino-4'-nitrostilbene and disperse red 1 chromophores doped into poly(Methyl methacrylate) guest-host systems. Charge symmetry is also being studies using thermal pulse experiments. Preliminary result show that the charges are distributed linearly in the sample. More tests will be performed in search of any local charge distribution inhomogeneities. An interferometric technique with in-situ poling was used to probe the poling field- induced molecular alignment of the chromophores as a function of temperature. Results are showing the dependence of poling on electric fields (magnitude and polarity). Integrated systems will further reveal the loses in the films due to the field Dependent chromophore orientation.
Download or read book Organic Thin Films for Photonic Applications written by Warren Herman and published by OUP USA. This book was released on 2011-01-13 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book describes recent research in materials development, characterization techniques, and device development related to organic thin films for photonic applications.
Download or read book Diradicaloids written by Jishan Wu and published by CRC Press. This book was released on 2022-04-01 with total page 638 pages. Available in PDF, EPUB and Kindle. Book excerpt: π-Conjugated molecules with an even number of π-electrons usually have a closed-shell ground state. However, recent studies have demonstrated that a certain type of molecules could show open-shell singlet ground state and display diradical-like (diradicaloid) behavior. Their electronic structure can be understood in terms of the “diradical character” and “aromaticity” concepts. They display very different electronic properties from traditional closed-shell π-conjugated molecules and could be used as next-generation molecular materials. This book provides a comprehensive review on the chemistry, physics, and material applications of open-shell singlet diradicaloids. Particularly, it elaborates the fundamental structure–diradical character–electronic property relationships both theoretically and experimentally. The book has been written by leading scientists in the field from Japan, Germany, Spain, Italy, China, and Singapore.
Download or read book Ultrafast Dynamics In Molecules Nanostructures And Interfaces Selected Lectures Presented At Symposium On Ultrafast Dynamics Of The 7th International Conference On Materials For Advanced Technologies written by Guglielmo Lanzani and published by World Scientific. This book was released on 2014-01-22 with total page 304 pages. Available in PDF, EPUB and Kindle. Book excerpt: Primary events in natural systems or devices occur on extremely short time scales, and yet determine in many cases the final performance or output. For this reason research in ultrafast science is of primary importance and impact in both fundamental research as well as its applications. This book reviews the advances in the field, addressing timely and open questions such as the role of quantum coherence in biology, the role of excess energy in electron injection at photovoltaic interfaces or the dynamics in quantum confined structures (e.g. multi carrier generation). The approach is that of a monograph, with a broad tutorial introduction and an overview of the recent results. This volume includes selected lectures presented at Symposium on Ultrafast Dynamics of the 7th International Conference on Materials for Advanced Technologies.
Download or read book Organic Optoelectronic Materials written by Yongfang Li and published by Springer. This book was released on 2015-05-30 with total page 402 pages. Available in PDF, EPUB and Kindle. Book excerpt: 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.
Download or read book Halide Perovskites written by Tze-Chien Sum and published by John Wiley & Sons. This book was released on 2019-03-25 with total page 312 pages. Available in PDF, EPUB and Kindle. Book excerpt: Real insight from leading experts in the field into the causes of the unique photovoltaic performance of perovskite solar cells, describing the fundamentals of perovskite materials and device architectures. The authors cover materials research and development, device fabrication and engineering methodologies, as well as current knowledge extending beyond perovskite photovoltaics, such as the novel spin physics and multiferroic properties of this family of materials. Aimed at a better and clearer understanding of the latest developments in the hybrid perovskite field, this is a must-have for material scientists, chemists, physicists and engineers entering or already working in this booming field.
Download or read book Principles of Nonlinear Optical Spectroscopy written by Shaul Mukamel and published by Oxford University Press on Demand. This book was released on 1999 with total page 543 pages. Available in PDF, EPUB and Kindle. Book excerpt: This textbook presents a systematic and unifying viewpoint for a wide class of nonlinear spectroscopic techniques in time domain and frequency domain. It is directed towards active researchers in physics, optics, chemistry, and materials science, as well as graduate students who enter this complex and rapidly developing field. Nonlinear optical interactions of laser fields with matter provide powerful spectroscopic tools for the understanding of microscopic interactions and dynamic processes. One of the major obstacles facing researchers in this field, however, is the flood of experimental techniques and terminologies, which create a serious language barrier. The general microscopic correlation function approach to the nonlinear optical response developed in this book is essential for understanding the relationships among different techniques and a comparison of their information content, the design of new measurements, and for a systematic comparison of the optical response of different systems such as dyes in solutions, atoms and molecules in the gas phase, liquids, molecular aggregates and superlatives, and semiconductor nanostructures. The approach is based on formulating the nonlinear response by representing the state of matter by the density matrix and following its evolution on Liouville space. Current active research areas such as femtosecond time-domain techniques, semi-classical and wave-packet dynamics, pulse shaping, pulse locking, exciton confinement, and the interplay of electronic, nuclear and field coherence are emphasized. The material has been developed from the author's highly successful interdisciplinary course at the University of Rochester attended by science and engineering graduate students.
Download or read book Colloidal Quantum Dot Optoelectronics and Photovoltaics written by Gerasimos Konstantatos and published by Cambridge University Press. This book was released on 2013-11-07 with total page 329 pages. Available in PDF, EPUB and Kindle. Book excerpt: Captures the most up-to-date research in the field, written in an accessible style by the world's leading experts.
Download or read book Fundamentals of Sum Frequency Spectroscopy written by Y. R. Shen and published by Cambridge University Press. This book was released on 2016-02-18 with total page 570 pages. Available in PDF, EPUB and Kindle. Book excerpt: The first book on the topic, and written by the founder of the technique, this comprehensive resource provides a detailed overview of sum-frequency spectroscopy, its fundamental principles, and the wide range of applications for surfaces, interfaces, and bulk. Beginning with an overview of the historical context, and introductions to the basic theory of nonlinear optics and surface sum-frequency generation, topics covered include discussion of different experimental arrangements adopted by researchers, notes on proper data analysis, an up-to-date survey commenting on the wide range of successful applications of the tool, and a valuable insight into current unsolved problems and potential areas to be explored in the future. With the addition of chapter appendices that offer the opportunity for more in-depth theoretical discussion, this is an essential resource that integrates all aspects of the subject and is ideal for anyone using, or interested in using, sum-frequency spectroscopy.
Download or read book Exciton Dynamics in Lead Halide Perovskite Nanocrystals written by Bernhard Johann Bohn and published by Springer Nature. This book was released on 2021-05-18 with total page 169 pages. Available in PDF, EPUB and Kindle. Book excerpt: Less than a decade ago, lead halide perovskite semiconductors caused a sensation: Solar cells exhibiting astonishingly high levels of efficiency. Recently, it became possible to synthesize nanocrystals of this material as well. Interestingly; simply by controlling the size and shape of these crystals, new aspects of this material literally came to light. These nanocrystals have proven to be interesting candidates for light emission. In this thesis, the recombination, dephasing and diffusion of excitons in perovskite nanocrystals is investigated using time-resolved spectroscopy. All these dynamic processes have a direct impact on the light-emitting device performance from a technology point of view. However, most importantly, the insights gained from the measurements allowed the author to modify the nanocrystals such that they emitted with an unprecedented quantum yield in the blue spectral range, resulting in the successful implementation of this material as the active layer in an LED. This represents a technological breakthrough, because efficient perovskite light emitters in this wavelength range did not exist before.
