Download or read book Interface Studies of Organic transition Metal Oxide with Organic Semiconductors and the Interfaces in the Perovskite Solar Cell written by Chenggong Wang and published by . This book was released on 2015 with total page 201 pages. Available in PDF, EPUB and Kindle. Book excerpt: "In recent decades, research and development of organic based semiconductor devices have attracted intensive interests. One of the most essential elements is to understand the electronic structures at various interfaces involved in these devices since the interface properties control many of the critical electronic processes. It is thus necessary to study the electronic properties of the organic semiconductors with surface analytical tools to improve the understanding of the fundamental mechanisms involved in the interface formation. This thesis covers the experimental investigations on some of the most interesting topics raised in the recent development of organic electronic devices. The thesis intends to reveal the physical processes at the interface and their contribution to the device performance with photoemission and inverse photoemission investigations on the evolution of the occupied and unoccupied electronic structures. I will report a substantial difference in the electron affinity of CuPc on two substrates as the orientations of CuPc are different. I will also illustrate that the CuPc has standing up configuration on one monolayer of C60 on SiO2 while lying down on one monolayer of C60 on HOPG. Meanwhile, the CuPc on more than one monolayers of C60 on different substrates show that the substrate orientation effect vanished. Then I will propose a two-stage model to describe the bulk doping effect of C60 by molybdenum oxide. I will also demonstrate that the doping effect of C60 by ultra-thin layer molybdenum oxide is weaker than that by interface doping and bulk doping. I will demonstrate that for Au on CH3NH3PbI3, hole accumulation occurs at the vicinity of the interface, facilitating hole transfer from CH3NH3PbI3 to Au. I will show a strong initial shift of core levels to lower binding energy in C60 on CH3NH3PbI3 interface, which indicates that electrons transfer from the perovskite film to C60 molecules. I will further demonstrate that the molybdenum oxide surface can be passivated by approximately two monolayers of organic thin films against exposure to air. I will discuss the mechanism for how oxygen plasma treatment effectively recovers the high work function drop of molybdenum oxide by air exposure. I will also show that a small energy offset at Pentacen/C60heterojunction makes it easy to transfer electrons from Pentacene to C60 even under a small applied bias, facilitating the occurrence of charge generation"--Pages xi-xii.

Download or read book The Future of Semiconductor Oxides in Next Generation Solar Cells written by Monica Lira-Cantu and published by Elsevier. This book was released on 2017-09-19 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: The Future of Semiconductor Oxides in Next-Generation Solar Cells begins with several chapters covering the synthesis of semiconductor oxides for NGSCs. Part II goes on to cover the types and applications of NGSCs currently under development, while Part III brings the two together, covering specific processing techniques for NGSC construction. Finally, Part IV discusses the stability of SO solar cells compared to organic solar cells, and the possibilities offered by hybrid technologies. This comprehensive book is an essential reference for all those academics and professionals who require thorough knowledge of recent and future developments in the role of semiconductor oxides in next generation solar cells. - Unlocks the potential of advanced semiconductor oxides to transform Next Generation Solar Cell (NGSC) design - Full coverage of new developments and recent research make this essential reading for researchers and engineers alike - Explains the synthesis and processing of semiconductor oxides with a view to their use in NGSCs

Download or read book Interfaces of Electrical Contacts in Organic Semiconductor Devices written by Korhan Demirkan and published by ProQuest. This book was released on 2008 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Progress in organic semiconductor devices relies on better understanding of interfaces as well as material development. The engineering of interfaces that exhibit low resistance, low operating voltage and long-term stability to minimize device degradation is one of the crucial requirements. Photoelectron spectroscopy is a powerful technique to study the metal-semiconductor interfaces, allowing: (i) elucidation of the energy levels of the semiconductor and the contacts that determine Schottky barrier height, (ii) inspection of electrical interactions (such as charge transfer, dipole formation, formation of induced density of states or formation of polaron/bi-polaron states) that effect the energy level alignment, (iii) determination of interfacial chemistry, and (iv) estimation of interface morphology. In this thesis, we have used photoelectron spectroscopy extensively for detailed analysis of the metal organic semiconductor interfaces. In this study, we demonstrate the use of photoelectron spectroscopy for construction of energy level diagrams and display some results related to chemical tailoring of materials for engineering interfaces with lowered Schottky barriers. Following our work on the energy level alignment of poly(p-phenyene vinylene) based organic semiconductors on various substrates [Au, indium tin oxide, Si (with native oxide) and Al (with native oxide)], we tested controlling the energy level alignment by using polar self assembled molecules (SAMs). Photoelectron spectroscopy showed that, by introducing SAMs on the Au surface, we successfully changed the effective work function of Au surface. We found that in this case, the change in the effective work function of the metal surface was not reflected as a shift in the energy levels of the organic semiconductor, as opposed to the results achieved with different substrate materials. To investigate the chemical interactions at the metal/organic interface, we studied the metallization of poly(2-methoxy-5,2'-ethyl-hexyloxy-phenylene vinylene) (MEH-PPV), polystyrene (PS) and ozone treated polystyrene (PS-O3) surfaces by thermal deposition of aluminum. Photoelectron spectroscopy showed the degree of chemical interaction between Al and each polymer, for MEH-PPV, the chemical interactions were mainly through the C-O present in the side chain of the polymer structure. The chemical interaction of Al with polystyrene was less significant, but it showed a dramatic increase after ozone treatment of the polystyrene surface (due to the formation of exposed oxygen sites). Formation of metal oxide and metal-organic compound is detected during the Al metallization of MEH-PPV and ozone-treated PS surfaces. Our results showed that the condensation of Al on polymer surfaces is highly dependent on surface reactivity. Enormous differences were observed for the condensation coefficient of Al on PS and PS-O3 surfaces. For the inert PS surface, results showed that Al atoms poorly wet the polymer surface and form distributed clusters at the surface. Results on reactive polymer surfaces suggest morphology reminiscent of a Stranski- Krastanov-type growth and high contact area. Many studies have shown that the insertion of a thin interlayer of the oxide or fluoride of alkali or alkaline metals between the low work function electrode and the organic semiconductor layers dramatically lowers the onset voltage and increases the efficiency compared to identical devices without the insulating layer. Various modes have been suggested for the mechanism of device performance enhancement. We have investigated the chemical and electrical interaction of (i) LiF with MEH-PPV, (ii) Al with MEH-PPV in the presence of a thin LiF layer at the interface, and finally (iii) the interaction of Al with LiF. AFM and XPS data showed that LiF forms island on the surface. Our data in agreement with various existing models suggested the (i) alteration in the electronic properties under applied bias, (ii) doping of the organic semiconductor, (iii) formation of metal alloy (Au-Li). In addition to the possible electrical modifications at the interface suggested previously, our data also suggest a change in the film growth on LiF modified surfaces.

Download or read book The Future of Semiconductor Oxides in Next Generation Solar Cells written by Monica Lira-Cantu and published by . This book was released on 2017 with total page 568 pages. Available in PDF, EPUB and Kindle. Book excerpt: 4.1.2 Doped NiO -- 4.1.2.1 Cu-Doped NiO -- 4.1.2.2 Li, Mg-Doped NiO -- 4.2 CuOx -- 4.3 Others -- References -- Chapter 5 Metal Oxide-Based Charge Extraction and Recombination Layers for Organic Solar Cells -- 5.1 Introduction -- 5.2 High Work-Function Metal-Oxide Hole Extraction Layers -- 5.3 Low Work-Function Metal-Oxide Electron Extraction Layers -- 5.4 Organic Multijunction Solar Cells With Metal-Oxide Recombination Layers -- 5.5 Summary and Outlook -- Acknowledgments -- References -- Chapter 6 Dye-Sensitized Solar Cells -- 6.1 Introduction and Historical Overview -- 6.2 DSSC Operation: Basic Principles -- 6.2.1 Useful Processes -- 6.2.2 Deleterious Processes -- 6.2.3 Incident Photon-to-Current Efficiency -- 6.2.3.1 Light Harvesting Efficiency -- 6.2.3.2 Electron Injection Efficiency -- 6.2.3.3 Electron Collection Efficiency -- 6.2.3.4 Sensitizer Turnover Number -- 6.2.3.5 Energy Conversion Efficiency -- 6.3 Redox Mediators in the Electrolyte -- 6.3.1 Energetics at the Adsorbed Dye-Electrolyte Interface -- 6.3.1.1 Redox Potential and Fermi Level -- 6.3.1.2 Energetics of Regeneration and Recombination at the Photoelectrode -- 6.3.2 Considerations Regarding Successful Redox Mediator Operation -- 6.3.3 Description of Some Efficient Redox Mediator Systems -- 6.3.3.1 Iodide -- 6.3.3.2 Cobalt Coordination Complexes -- 6.3.3.3 Copper Coordination Complexes -- 6.3.3.4 Nitroxide Radicals -- 6.3.3.5 Mixed Mediators -- 6.4 Organic Solid-State Charge Hole Conductors -- 6.4.1 General Considerations -- 6.4.2 Small Molecular Size Hole Conductors -- 6.4.3 Conducting Polymer Hole Conductors -- References -- Chapter 7 Semiconducting Metal Oxides for High Performance Perovskite Solar Cells -- 7.1 Introduction -- 7.2 n-i-p Structure -- 7.2.1 Evolution of Device Structure and Metal Oxide Selective Contacts

Download or read book Transition Metal Oxides in Organic Electronics written by Mark Greiner and published by . This book was released on 2012 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book The Impact of Interfaces on the Performance of Organic Photovoltaic Cells written by Roland Steim and published by KIT Scientific Publishing. This book was released on 2010 with total page 156 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaic is an attractive technology to solve future energy supply scenarios. To further increase the potential of this technology novel absorber materials and interface materials have to be developed. In this work the paramount importance of interface materials for efficient as well as stable organic photovoltaic cells and modules is demonstrated. The general requirements of interface materials are elaborated and properties of a novel interface material which meets the demands are investigated experimentally and by simulations.

Download or read book Multifunctional Nanostructured Metal Oxides for Energy Harvesting and Storage Devices written by Vijay B. Pawade and published by CRC Press. This book was released on 2020-05-21 with total page 280 pages. Available in PDF, EPUB and Kindle. Book excerpt: Metal oxide nanoparticles exhibit potential applications in energy and environmental fields, such as solar cells, fuel cells, hydrogen energy, and energy storage devices. This book covers all points from synthesis, properties, and applications of transition metal oxide nanoparticle materials in energy storage and conversion devices. Aimed at graduate-level students and researchers associated with the energy and environment sector, this book addresses the application of nontoxic and environmentally friendly metal oxide materials for a clean environment and deals with synthesis properties and application metal oxides materials for energy conversion, energy storage, and hydrogen generation.

Download or read book Oxide Semiconductors for Solar Energy Conversion written by Janusz Nowotny and published by CRC Press. This book was released on 2016-04-19 with total page 419 pages. Available in PDF, EPUB and Kindle. Book excerpt: Oxide semiconductors, including titanium dioxide (TiO2), are increasingly being considered as replacements for silicon in the development of the next generation of solar cells. Oxide Semiconductors for Solar Energy Conversion: Titanium Dioxide presents the basic properties of binary metal oxide semiconductors and the performance-related properties

Download or read book Study of the Impact of Microstructures and Interface Energetics in Perovskite and Organic Solar Cells written by Chuanpeng Jiang and published by . This book was released on 2018 with total page 191 pages. Available in PDF, EPUB and Kindle. Book excerpt:

Download or read book Hybrid Organic Inorganic Perovskites written by Li Wei and published by John Wiley & Sons. This book was released on 2020-10-19 with total page 290 pages. Available in PDF, EPUB and Kindle. Book excerpt: Hybrid organic-inorganic perovskites (HOIPs) have attracted substantial interest due to their chemical variability, structural diversity and favorable physical properties the past decade. This materials class encompasses other important families such as formates, azides, dicyanamides, cyanides and dicyanometallates. The book summarizes the chemical variability and structural diversity of all known hybrid organic-inorganic perovskites subclasses including halides, azides, formates, dicyanamides, cyanides and dicyanometallates. It also presents a comprehensive account of their intriguing physical properties, including photovoltaic, optoelectronic, dielectric, magnetic, ferroelectric, ferroelastic and multiferroic properties. Moreover, the current challenges and future opportunities in this exciting field are also been discussed. This timely book shows the readers a complete landscape of hybrid organic-inorganic pervoskites and associated multifuctionalities.

Download or read book Interface Engineering and Morphology Study of Thin Film Organic Inorganic Halide Perovskite Optoelectronic Devices written by Lei Meng and published by . This book was released on 2017 with total page 161 pages. Available in PDF, EPUB and Kindle. Book excerpt: Solar energy harvesting through photovoltaic conversion has gained great attention as a sustainable and environmentally friendly solution to meet the rapidly increasing global energy demand. Currently, the high cost of solar-cell technology limits its widespread use. This situation has generated considerable interest in developing alternative solar-cell technologies that reduce cost through the use of less expensive materials and processes. Perovskite solar cells provide a promising low-cost technology for harnessing this energy source. In Chapter two, a moisture-assist method is introduced and studied to facilitate grain growth of solution processed perovskite films. As an approach to achieve high-quality perovskite films, I anneal the precursor film in a humid environment (ambient air) to dramatically increase grain size, carrier mobility, and charge carrier lifetime, thus improving electrical and optical properties and enhancing photovoltaic performance. It is revealed that mild moisture has a positive effect on perovskite film formation, demonstrating perovskite solar cells with 17.1% power conversion efficiency. Later on, in Chapter four, an ultrathin flexible device delivering a PCE of 14.0% is introduced. The device is based on silver-mesh substrates exhibiting superior durability against mechanical bending. Due to their low energy of formation, organic lead iodide perovskites are also susceptible to degradation in moisture and air. The charge transport layer therefore plays a key role in protecting the perovskite photoactive layer from exposure to such environments, thus achieving highly stable perovskite-based photovoltaic cells. Although incorporating organic charge transport layers can provide high efficiencies and reduced hysteresis, concerns remain regarding device stability and the cost of fabrication. In this work, perovskite solar cells that have all solution-processed metal oxide charge transport layers were demonstrated. Stability has been significantly improved compared with cells made with organic layers. Degradation mechanisms were investigated and important guidelines were derived for future device design with a view to achieving both highly efficient and stable solar devices. Organometal halide based perovskite material has great optoelectronic proprieties, for example, shallow traps, benign grain boundaries and high diffusion length. The perovskite LEDs show pure electroluminescence (EL) with narrow full width at half maximum (FWHM), which is an advantage for display, lighting or lasing applications. In chapter five, perovskite LEDs are demonstrated employing solution processed charge injection layers with a quantum efficiency of 1.16% with a very low driving voltage.

Download or read book The Physics of Solar Energy Conversion written by Juan Bisquert and published by CRC Press. This book was released on 2020-06-09 with total page 686 pages. Available in PDF, EPUB and Kindle. Book excerpt: Research on advanced energy conversion devices such as solar cells has intensified in the last two decades. A broad landscape of candidate materials and devices were discovered and systematically studied for effective solar energy conversion and utilization. New concepts have emerged forming a rather powerful picture embracing the mechanisms and limitation to efficiencies of different types of devices. The Physics of Solar Energy Conversion introduces the main physico-chemical principles that govern the operation of energy devices for energy conversion and storage, with a detailed view of the principles of solar energy conversion using advanced materials. Key Features include: Highlights recent rapid advances with the discovery of perovskite solar cells and their development. Analyzes the properties of organic solar cells, lithium ion batteries, light emitting diodes and the semiconductor materials for hydrogen production by water splitting. Embraces concepts from nanostructured and highly disordered materials to lead halide perovskite solar cells Takes a broad perspective and comprehensively addresses the fundamentals so that the reader can apply these and assess future developments and technologies in the field. Introduces basic techniques and methods for understanding the materials and interfaces that compose operative energy devices such as solar cells and solar fuel converters.

Download or read book Photovoltaic Solar Energy written by Wilfried van Sark and published by John Wiley & Sons. This book was released on 2024-07-29 with total page 645 pages. Available in PDF, EPUB and Kindle. Book excerpt: Photovoltaic Solar Energy Thoroughly updated overview of photovoltaic technology, from materials to modules and systems Volume 2 of Photovoltaic Solar Energy provides fundamental and contemporary knowledge about various photovoltaic technologies in the framework of material science, device physics of solar cells, chemistry for manufacturing, engineering of PV modules, and the design aspects of photovoltaic applications, with the aim of informing the reader about the basic knowledge of each aspect of photovoltaic technologies and applications in the context of the most recent advances in science and engineering. The text is written by leading specialists for each topic in a concise manner and includes the most recent references for deeper study. Moreover, the book gives insights into possible future developments in the field of photovoltaics. The book builds on the success of Volume 1 of Photovoltaic Solar Energy, which was published by Wiley in January 2017. As science and technology is progressing fast in some areas of photovoltaics, several topics needed to be readdressed. Volume 2 also covers some basic aspects of the subject that were not addressed in Volume 1. Sample topics covered in Photovoltaic Solar Energy include: Solar Irradiance Resources Crystalline Silicon Technologies (Cz Ingots, TOPCon, Heterojunction, Passivating contacts, Hydrogenation and Carrier Induced Degradation) Perovskite and Tandem solar cells Characterization and Measurements PV Modules PV Systems and Applications (integration in buildings, agriculture, water, vehicles) Sustainability Providing comprehensive coverage of the subject, Photovoltaic Solar Energy is an essential resource for undergraduate and graduate students in science or engineering, young professionals in PV research or the PV industry, professors, teachers, and PV specialists who want to receive updated information. A scientific or engineering degree is a prerequisite.

Download or read book Organic Solar Cells written by Wolfgang Tress and published by Springer. This book was released on 2014-11-22 with total page 474 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers in a textbook-like fashion the basics or organic solar cells, addressing the limits of photovoltaic energy conversion and giving a well-illustrated introduction to molecular electronics with focus on the working principle and characterization of organic solar cells. Further chapters based on the author’s dissertation focus on the electrical processes in organic solar cells by presenting a detailed drift-diffusion approach to describe exciton separation and charge-carrier transport and extraction. The results, although elaborated on small-molecule solar cells and with focus on the zinc phthalocyanine: C60 material system, are of general nature. They propose and demonstrate experimental approaches for getting a deeper understanding of the dominating processes in amorphous thin-film based solar cells in general. The main focus is on the interpretation of the current-voltage characteristics (J-V curve). This very standard measurement technique for a solar cell reflects the electrical processes in the device. Comparing experimental to simulation data, the author discusses the reasons for S-Shaped J-V curves, the role of charge carrier mobilities and energy barriers at interfaces, the dominating recombination mechanisms, the charge carrier generation profile, and other efficiency-limiting processes in organic solar cells. The book concludes with an illustrative guideline on how to identify reasons for changes in the J-V curve. This book is a suitable introduction for students in engineering, physics, material science, and chemistry starting in the field of organic or hybrid thin-film photovoltaics. It is just as valuable for professionals and experimentalists who analyze solar cell devices.

Download or read book Evaluation of Chemical and Electronic Properties of Photovoltaic Materials at Interfaces in Solar Cell Devices written by Amira Ramadan Alghamdi and published by . This book was released on 2023 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic photovoltaics (OPVs) and perovskite solar cells (PSCs) have come a long way in recent years, reaching power conversion efficiencies of ~19% and 25.7%, respectively, for a single cell test. This advance was brought about by concurrent progress in materials design and synthesis and interfacial engineering. Interfaces formed between different layers in solar cells dictate device characteristics and degradation. This thesis is dedicated to interfacial engineering and the investigation of a range of materials and modifications with OPV and PSC applications front of mind. In particular, the focus is on studying the electronic properties and energy band structures at the interface's layers in OPVs and PSCs and discovering the impact of the interface on device performance. In this thesis, in terms of OPV structure, a novel potential of organic interface layers was deployed with a range of active materials as a replacement for an inorganic interface layer due to its flexibility, ease of fabrication and potentially more cost-effective design than the conventional inorganic interfaces. The electronic structure and the charge transfer mechanism at the polymer cathode interface layer (CIL)/active layers interface are discussed. A powerful combination of experimental techniques was applied to gain fundamental understanding of the chemical and electronic properties and engineering of the interfaces formed with polymer CIL and active materials. The valance electron structure of new polymer (CIL) of P(NDI3N-T-Br) with TQ1 and N2200 active layers were first investigated where a mixing of phases at the interface was determined. The results show that the dipole formation between the donor, acceptor and P(NDI3N-T-Br) was observed, which enhanced electronic structure at the interfaces and facilitated charge transport over the interface. This energy level alignment meets the expectation of using P(NDI3N-T-Br) as an interface layer in blocking the hole transfer to the interface layer while TQ1:N2200 is used as the photovoltaic active layer. Consequently, another new CIL, P(NDI3N-F8-Br), with PTB7-Th and ITIC is investigated. A comprehensive study of the energy structure of P(NDI3N-F8-Br) with PTB-Th: ITIC deposited in the case of inverted devices is constructed. The results show that P(NDI3N-F8-Br) can work as a hole-blocking layer. Simultaneously, however, the electrons transferring from ITIC were blocked by the P(NDI3N-F8-Br) interface. Investigating the electronic structure of new organic cathode materials thus lead to a better understanding of the charge energetics at the interface and down-selection of the device structure. To achieve a comprehensive understanding, comparison has been made to the interface of PTB7-Th: ITIC-incorporated zinc oxide (ZnO) as a conventional inorganic interface layer. The results show that the active layers worked proficiently with ZnO. As a result, ZnO blocks the holes and extracting the electrons from the ITIC layer, which is desired. Overall, dipole formation was observed at the interfaces of P(NDI3N-F8-Br) and ZnO with active layers. Finally, the distribution of the charge transport component of PTB7-Th: ITIC has been studied to fill the knowledge gap on this type of study in this field. Thus, the component distribution at the surface region of the PTB7-Th: ITIC blend was investigated with the effect of the additive p-anisaldehyde (AA) on the components, which formed one side of the interface of the blend with the MoOx electrode. This finding contributes to an understanding of the interaction between the donor material and the high work function electrode/interface material. Following our research on OPVs, another study on PSCs is conducted. In PSCs, sputtered NiOx (sp-NiOx) is used as hole transport material in PSCs due to the mobility of its holes, compatibility of the stability, easy fabrication and Fermi level position suitable for hole extraction. However, unavoidable defects in sp-NiOx or perovskite films can affect solar efficiency. Thus, self-assembled monolayer (SAM) MeO-2PACz was inserted between the sp-NiOx and perovskite film, which can contribute to reducing defects and improving the device's performance. The results showed that the MeO-2PACz interface enhances perovskite film quality by reducing charge recombination at the sp-NiOx/perovskite interface. It also passivates defects in the sp-NiOx surface and perovskite layer. The overall outcome resulted in an improvement in the device efficiency from 11.9% to 17.2%.

Download or read book Understanding the Morphology at Donor acceptor Interfaces in Organic Semiconductors written by Zixuan Guo and published by . This book was released on 2022 with total page 0 pages. Available in PDF, EPUB and Kindle. Book excerpt: Organic electronic devices, including organic photovoltaics (OPV), organic light-emitting diodes (OLEDs), and organic field-effect transistors (OFETs), have become increasingly important in consumer electronic applications due to the development of organic semiconductors, including organic small molecules, and conjugated polymers. They have advantages such as light weight, flexibility/stretchability, and the ability for roll-to-roll manufacturing. The structure and mechanism of organic devices are analogous to inorganic semiconductor devices, where donor materials (p-type) and acceptor materials (n-type) are used to create interfaces. To build high-performance organic electronic devices, it is essential to understand functionalities of organic heterojunction because they are building blocks of electronics. Organic heterojunction is interfaces created between donor and acceptor organic semiconductors. Exciting electronic action of devices occurs at organic interfaces. From a fundamental viewpoint, the role of interfaces must have optimal electronic and physical communication to yield highly efficient devices. From a technological viewpoint, one must understand, control, and have a rational design of the desired electronic and optical properties at organic interfaces for the development of different electronics and a host of potential new device concepts that have not yet been developed or realized. In this dissertation, we will use organic semiconductors for organic photovoltaics (OPV) as an example to investigat organic heterojunction interfaces, including interface fabrication, epitaxy, morphology control, and characterization, with the aim of building high-performance devices with good stability. We begin by discussing the growth of organic single-crystalline crystals with controlled orientations. Materials used are two small molecules: zinc phthalocyanine (ZnPc, p-type) and 3,4,9,10-perylenetetracarboxylic dianhydride (PTCDA, n-type). In this study, a self-built vertical physical vapor transport (v-PVT) chamber is used for crystallization, and a graphene-coated substrate is used to control molecular packing. Although ZnPc and PTCDA have a planar molecular shape and face-on packing motif on graphene, we find that they have different growth modes. Such growth mechanism difference can be explained by competition between intermolecular and molecule-graphene interactions. We then continue the abovementioned study by building model heterojunctions on graphene substrates using ZnPc and PTCDA. We discover that thermodynamics and kinetics of the system affect P-N junction morphology. We find that ZnPc and PTCDA form the "line-on-line" organic weak epitaxy at heterojunction interfaces from X-ray studies and crystallography refinement. We also verify that P-N junctions can generate electron-hole pairs. This work will advance the knowledge and create enabling opportunities to fabricate single-crystalline-oriented nanostructures. Besides using organic small molecules, we also explore the structure-property-performance relationship of conjugated block copolymers (BCPs) for OPV applications. In this work, a new donor-acceptor BCP is synthesized and added into polymer blend solar cells. We find that adding BCP could potentially retain the relative degree of crystallinity of [pi]-[pi] stacking regions, and decrease the detrimental interaction between donor polymer and electrode under thermal stress, thus improving the solar device's thermal stability by 30%. Finally, we explore the possibility of using graphene engineering for epitaxial growth dynamics control of organic small molecules. We determine that two distinct, alternating morphologies of ZnPc crystals are simultaneously observed on a single epitaxial SiC-graphene substrate. We hypothesize that the different morphologies arise from electronic structure and surface energy differences of underlying SiC-graphene regions ZnPc is grown on. The result will enable selective patterning of organic semiconductors for use in advanced warfare device applications. We hope these studies throughout this work will advance knowledge on fundamental crystallization mechanisms, interface engineering, morphology control, and characterization in organic crystalline systems. This work could further produce various future architectures for different applications in organic electronics.

Download or read book Evaluation of Transition Metal Oxide as Carrier selective Contacts for Silicon Heterojunction Solar Cells written by and published by . This book was released on 2015 with total page 1 pages. Available in PDF, EPUB and Kindle. Book excerpt: "Reducing light absorption in the non-active solar cell layers, while enabling the extraction of the photogenerated minority carriers at quasi-Fermi levels are two key factors to improve current generation and voltage, and therefore efficiency of silicon heterojunction solar devices. To address these two critical aspects, transition metal oxide materials have been proposed as alternative to the n- and p-type amorphous silicon used as electron and hole selective contacts, respectively. Indeed, transition metal oxides such as molybdenum oxide, titanium oxide, nickel oxide or tungsten oxide combine a wide band gap typically over 3 eV with a band structure and theoretical band alignment with silicon that results in high transparency to the solar spectrum and in selectivity for the transport of only one carrier type. Improving carrier extraction or injection using transition metal oxide has been a topic of investigation in the field of organic solar cells and organic LEDs; from these pioneering works a lot of knowledge has been gained on materials properties, ways to control these during synthesis and deposition, and their impact on device performance. Recently, the transfer of some of this knowledge to silicon solar cells and the successful application of some metal oxide to contact heterojunction devices have gained much attention. In this contribution, we investigate the suitability of various transition metal oxide films (molybdenum oxide, titanium oxide, and tungsten oxide) deposited either by thermal evaporation or sputtering as transparent hole or electron selective transport layer for silicon solar cells. In addition to systematically characterize their optical and structural properties, we use photoemission spectroscopy to relate compound stoichiometry to band structure and characterize band alignment to silicon. The direct silicon/metal oxide interface is further analyzed by quasi-steady state photoconductance decay method to assess the quality of surface passivation. In complement, we construct full device structures incorporating in some cases surface passivation schemes, with measured initial conversion efficiency over 15% and evaluate the carrier transport properties using temperature-dependent current-voltage and capacitance-voltage measurements. With this detailed characterization study, we aim at providing the framework to assess the potential of a material as a carrier selective contact and the understanding of how each of the aforementioned parameters on the metal oxide films influence the full solar cell operating performances.