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 On Exciton Vibration and Exciton Photon Interactions in Organic Semiconductors written by Antonios M. Alvertis and published by Springer Nature. This book was released on 2021-10-25 with total page 213 pages. Available in PDF, EPUB and Kindle. Book excerpt: What are the physical mechanisms that underlie the efficient generation and transfer of energy at the nanoscale? Nature seems to know the answer to this question, having optimised the process of photosynthesis in plants over millions of years of evolution. It is conceivable that humans could mimic this process using synthetic materials, and organic semiconductors have attracted a lot of attention in this respect. Once an organic semiconductor absorbs light, bound pairs of electrons with positively charged holes, termed `excitons’, are formed. Excitons behave as fundamental energy carriers, hence understanding the physics behind their efficient generation and transfer is critical to realising the potential of organic semiconductors for light-harvesting and other applications, such as LEDs and transistors. However, this problem is extremely challenging since excitons can interact very strongly with photons. Moreover, simultaneously with the exciton motion, organic molecules can vibrate in hundreds of possible ways, having a very strong effect on energy transfer. The description of these complex phenomena is often beyond the reach of standard quantum mechanical methods which rely on the assumption of weak interactions between excitons, photons and vibrations. In this thesis, Antonios Alvertis addresses this problem through the development and application of a variety of different theoretical methods to the description of these strong interactions, providing pedagogical explanations of the underlying physics. A comprehensive introduction to organic semiconductors is followed by a review of the background theory that is employed to approach the relevant research questions, and the theoretical results are presented in close connection with experiment, yielding valuable insights for experimentalists and theoreticians alike.

Download or read book Studies of Singlet Exciton Fission in Perylenediimide Films and Triplet Exciton Transfer at Organic inorganic Interfaces written by Jon Alexander Bender and published by . This book was released on 2020 with total page 392 pages. Available in PDF, EPUB and Kindle. Book excerpt: Herein, I showcase three studies that have formed the backbone of my work at UT Austin. First, we studied singlet exciton fission (SF) in a common perylenediimide (PDI) derivative often used as a molecular organic semiconductor, C8-PDI, using pump-probe spectroscopy to model SF and singlet-singlet annihilation (SSA). Therein, we were surprised to report a SF rate orders of magnitude slower than predicted by computational studies of PDI dimers. In Chapter 3, we study a suite of six PDI derivatives that adopt different crystal structures to further assess the nature of SF in polycrystalline films grown on sapphire and fused-quartz. We developed a kinetic model across the PDI series based on the analysis of time-resolved photoluminescence, free from SSA contributions to kinetics that must otherwise be carefully modelled for TA data of these films. We confirm that Redfield theoretic approximations of the SF rate in these materials better captures the trend in kinetics implying the important role the charge-transfer character in these excitons play in mediating the process. The variation in intermolecular organization and associated changes in the Coulombic and exchange coupling between nearest-neighbor molecules correctly captures a qualitative trend in the observed SF rate, though the observed rates are an order of magnitude smaller than expected. We propose this discrepancy arises because the PDI dimer model we use for our predictive model for polycrystalline PDI thin films neglects changes in the excited state character/energetics that become important in strongly interacting molecular solids. The contents of Chapter 4 are then a study of colloidal suspensions of PbS nanocrystals (NC) decorated with a TIPS-pentacene ligand, 2-CP. We set out to search for evidence of the formation of spin-triplet excitons on the 2-CP ligands after photoexcitation of the PbS NC. Triplet exciton formation is observed with no clear observation of an intermediate charge separated species. However, an intermediary state is observed and carefully assigned to a surface associated state on the PbS NC. This hypothesis is further supported by the presence of a multitude of triplet excited states found in constrained DFT computations and fluence dependent pump-probe data providing evidence for the photopassivation the intermediate surface state. In totality, my studies have elucidated excited state dynamics in singlet fission capable polycrystalline films of perylenediimide molecules and contributed to our growing understanding of triplet exciton transfer between PbS NCs and molecular ligands

Download or read book Singlet Exciton Fission written by Nicholas John Thompson and published by . This book was released on 2014 with total page 147 pages. Available in PDF, EPUB and Kindle. Book excerpt: Singlet exciton fission transforms a single molecular excited state into two excited states of half the energy. When used in solar cells it can double the photocurrent from high energy photons increasing the maximum theoretical power efficiency to greater than 40%. The steady state singlet fission rate can be perturbed under an external magnetic field. I utilize this effect to monitor the yield of singlet fission within operating solar cells. Singlet fission approaches unity efficiency in the organic semiconductor pentacene for layers more than 5 nm thick. Using organic solar cells as a model system for extracting photocurrent from singlet fission, I exceed the convention limit of 1 electron per photon, realizing 1.26 electrons per incident photon. One device architecture proposed for high power efficiency singlet fission solar cells coats a conventional inorganic semiconducting solar with a singlet fission molecule. This design requires energy transfer from the non-emissive triplet exciton to the semiconducting material, a process which has not been demonstrated. I prove that colloidal nanocrystals accept triplet excitons from the singlet fission molecule tetracene. This enables future devices where the combine singlet fission material and nanocrystal system energy transfer triplet excitons produced by singlet fission to a silicon solar cell.

Download or read book Emerging Strategies to Reduce Transmission and Thermalization Losses in Solar Cells written by Jonas Sandby Lissau and published by Springer Nature. This book was released on 2021-10-13 with total page 348 pages. Available in PDF, EPUB and Kindle. Book excerpt: The book describes emerging strategies to circumvent transmission and thermalization losses in solar cells, and thereby redefine the limits of solar power conversion efficiency. These strategies include the use of organic molecules and rare-earth metal materials. Approaches to augment the efficiency of these processes via near-field enhancement are described as well. This book includes a discussion of state-of-the-art implementations of these emerging strategies in solar cells, both internally, as in molecular intermediate band and charge carrier multiplication, and externally, such as photon up- and down-conversion. Tools for characterization are also provided. Written by leading researchers in the field, this book can be useful to both beginners and experienced researchers in solar energy.

Download or read book Singlet Exciton Fission in Unconventional Systems written by Andrew Musser and published by . This book was released on 2014 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Theories of Molecular Reaction Dynamics written by Niels E. Henriksen and published by Oxford University Press, USA. This book was released on 2008 with total page 391 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book deals with a central topic at the interface of chemistry and physics - the understanding of how the transformation of matter takes place at the atomic level. Building on the laws of physics, the book focuses on the theoretical framework for predicting the outcome of chemical reactions. The style is highly systematic with attention to basic concepts and clarity of presentation. Molecular reaction dynamics is about the detailed atomic-level description of chemical reactions. Based on quantum mechanics and statistical mechanics or, as an approximation, classical mechanics, the dynamics of uni- and bi-molecular elementary reactions are described. The book features a detailed presentation of transition-state theory which plays an important role in practice, and a comprehensive discussion of basic theories of reaction dynamics in condensed phases. Examples and end-of-chapter problems are included in order to illustrate the theory and its connection to chemical problems.

Download or read book Photosynergetic Responses in Molecules and Molecular Aggregates written by Hiroshi Miyasaka and published by Springer Nature. This book was released on 2020-09-05 with total page 593 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book compiles the accomplishments of the recent research project on photochemistry “Photosynergetics”, supported by the Ministry of Education, Culture, Sports, Science and Technology of Japan, aiming to develop and elucidate new methods and molecules leading to advanced utilization of photo-energies. Topics include photochemical responses induced by multiple excitation, multiphoton absorption, strong modulation of electronic states, developments of new photofunctional molecules, mesoscopic actuations induced by photoexcitation, and novel photoresponses in molecules and molecular assemblies. The authors stress that these approaches based on the synergetic interaction among many photons and many molecules enable the expansion of the accessibility to specific electronic states. As well, they explain how the development of reaction sequences and molecules/molecular assemblies ensure “additivity” and “integration” without loss of the photon energy, leading to new photoresponsive assemblies in meso- and macroscopic scales.

Download or read book Singlet Exciton Fission in a Linear Tetracene Tetramer1 written by and published by . This book was released on 2018 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advances in Chemical Physics Volume 162 written by Stuart A. Rice and published by John Wiley & Sons. This book was released on 2017-10-09 with total page 371 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Advances in Chemical Physics series provides the chemical physics field with a forum for critical, authoritative evaluations of advances in every area of the discipline. • This is the only series of volumes available that presents the cutting edge of research in chemical physics. • Includes contributions from experts in this field of research. • Contains a representative cross-section of research that questions established thinking on chemical solutions • Structured with an editorial framework that makes the book an excellent supplement to an advanced graduate class in physical chemistry or chemical physics

Download or read book Singlet Exciton Fission a Multi exciton Generation Process in Organic Semiconductor Solar Cells written by Priyadarshani Jadhav and published by . This book was released on 2012 with total page 115 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic semiconductor photovoltaics hold the promise of cheap production and low manufacturing setup costs. The highest efficiency seen in research labs, ~10% today, is still too low for production. In this work we explore implementations of a multiple exciton generation process, singlet exciton fission, to work around the Shockley-Queisser limit, according to which, all single junctions cells have a theoretical efficiency limit of 33.7%. This is the first implementation of a singlet fission photovoltaic. We measured a singlet fission efficiency of 72% at room temperature. We showed that singlet fission can be implemented in bulk heterojunction photovoltaics, which is an important result since some of the highest efficiency organic photovoltaics in the last 5 years have been bulk heterojunction structures. Secondly, we showed that the magnetic field effect can be used as a probe to investigate triplet dissociation in singlet fission devices. Thirdly, we implemented singlet fission photovoltaics, using the singlet fission material pentacene as donor and low bandgap infrared-absorptive lead chalcogenide quantum dots as acceptors. Singlet fission can enhance the efficiency of organic photovoltaics only if the fission material is paired with an absorptive low-energy-gap material. We find that pentacene triplet excitons dissociate at the pentacene/quantum dot heterojunctions with an internal quantum efficiency of 35%. Lastly, we investigate a series of materials to find a better acceptor in singlet fission photovoltaics using the methods and some results from the previous two investigations. We investigate device structures that pair pentacene and 6,13 diphenyl-pentacene as singlet fission donors with C60 , perylene diimides, PbS quantum dots and PbSe quantum dots as acceptors.

Download or read book Singlet Exciton Fission in Perylenediimide Thin Films written by Aaron Kristopher Le and published by . This book was released on 2019 with total page 340 pages. Available in PDF, EPUB and Kindle. Book excerpt: Singlet exciton fission (SF) is a process where a singlet exciton splits its energy with a neighboring molecule to form two lower energy triplet excitons. This is a process unique to organic molecules, and while intersystem crossing is typically slow in organic molecules due to small spin orbit coupling SF does not require a flip in spin to form these lower energy excitons and can occur on timescales extending from 10s of femtoseconds to nanoseconds. SF becomes efficient when the triplet energy is half of the energy of the singlet energy and occurs on timescales that outcompete deactivation pathways of the singlet exciton such as fluorescence. Efficient SF, or unity singlet to triplet interconversion via SF, has potential applications in improving the efficiencies of photovoltaic devices. Thermalization of high energy excitations in semiconductor photovoltaics pose a major loss channel for device efficiencies. An SF sensitizer can be incorporated into the device to absorb high energy excitations and following down conversion via SF to lower energy excitations thermalization losses can be mitigated. In this work we investigate SF in the perylenediimides (PDIs) in the solid state using ultrafast spectroscopy. The PDIs are deposited as polycrystalline thin films and structurally characterized to determine how the PDIs arrange in the thin films. SF is highly dependent on the intermolecular geometry of the of the participating chromophores, and the PDIs investigated in this work adopt different crystal structures in the solid state. This provides a platform to study the structure-function relationship of intermolecular geometry and SF. SF rates and triplet yield maxima are extracted from time-resolved emission and transient absorption spectroscopy with the aid of a kinetic models. The linear absorption and emission spectra suggest the singlet energy of the polycrystalline PDI films is lower than the monomeric PDIs due to aggregation. The potential disruption to the energetic requirement that the triplet energy be half the singlet would imply SF is an activated process in PDI thin films. We use a combination of temperature dependent time resolved emission and transient absorption spectroscopy to determine SF is endoergic in the PDI studied

Download or read book Singlet Exciton Fission in Acene Dimer and Diradicaloid Molecules written by Steven Lukman 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 Theory of Molecular Excitons written by A. Davydov and published by Springer. This book was released on 2013-11-11 with total page 319 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Advanced Concepts in Photovoltaics written by Arthur J. Nozik and published by Royal Society of Chemistry. This book was released on 2014-07-10 with total page 631 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaic systems enable the sun’s energy to be converted directly into electricity using semiconductor solar cells. The ultimate goal of photovoltaic research and development is to reduce the cost of solar power to reach or even become lower than the cost of electricity generated from fossil and nuclear fuels. The power conversion efficiency and the cost per unit area of the phototvoltaic system are critical factors that determine the cost of photovoltaic electricity. Until recently, the power conversion efficiency of single-junction photovoltaic cells has been limited to approximately 33% - the so-called Shockley-Queisser limit. This book presents the latest developments in photovoltaics which seek to either reach or surpass the Shockley-Queisser limit, and to lower the cell cost per unit area. Progress toward this ultimate goal is presented for the three generations of photovoltaic cells: the 1st generation based on crystalline silicon semiconductors; the 2nd generation based on thin film silicon, compound semiconductors, amorphous silicon, and various mesoscopic structures; and the 3rd generation based on the unique properties of nanoscale materials, new inorganic and organic photoconversion materials, highly efficient multi-junction cells with low cost solar concentration, and novel photovoltaic processes. The extent to which photovoltaic materials and processes can meet the expectations of efficient and cost effective solar energy conversion to electricity is discussed. Written by an international team of expert contributors, and with researchers in academia, national research laboratories, and industry in mind, this book is a comprehensive guide to recent progress in photovoltaics and essential for any library or laboratory in the field.

Download or read book Radiationless Transitions written by Sheng Lin and published by Elsevier. This book was released on 2012-12-02 with total page 440 pages. Available in PDF, EPUB and Kindle. Book excerpt: Radiationless Transitions is a critical discussion of research studies on the theory and experiments in radiationless transitions. This book is composed of nine chapters, and begins with discussions on the theory and experiment of photophysical processes of single vibronic levels and/or single rovibronic levels. The subsequent chapters deal with the spectroscopic investigations of intramolecular vibrational relaxation; the dynamics of molecular excitation by light; and the photophysical processes of small molecules in condensed phase. The discussions then shift to the high pressure effects on molecular luminescence and the internal conversion involving localized excitations, presenting one qualitative and one quantitative example, as well as the intersystem crossing with localized excitations. A chapter explores the energy transfer processes that occur after a molecule in solution is excited by light, with an emphasis on solid solutions in which the large amplitude molecular motion is largely quenched. This chapter also looks into the liquid solutions in which the molecules can translate and rotate under the influence of fluctuating forces from the liquid. The concluding chapter focuses on ultrafast processes. Researchers in the fields of physics, chemistry, and biology will benefit from this book.

Download or read book Electronic Processes in Organic Crystals written by Martin Pope and published by Oxford University Press. This book was released on 1982 with total page 821 pages. Available in PDF, EPUB and Kindle. Book excerpt: