Segui questo link per vedere altri tipi di pubblicazioni sul tema: P3HT polymer.
Tesi sul tema "P3HT polymer"
Cita una fonte nei formati APA, MLA, Chicago, Harvard e in molti altri stili
Vedi i top-50 saggi (tesi di laurea o di dottorato) per l'attività di ricerca sul tema "P3HT polymer".
Accanto a ogni fonte nell'elenco di riferimenti c'è un pulsante "Aggiungi alla bibliografia". Premilo e genereremo automaticamente la citazione bibliografica dell'opera scelta nello stile citazionale di cui hai bisogno: APA, MLA, Harvard, Chicago, Vancouver ecc.
Puoi anche scaricare il testo completo della pubblicazione scientifica nel formato .pdf e leggere online l'abstract (il sommario) dell'opera se è presente nei metadati.
Vedi le tesi di molte aree scientifiche e compila una bibliografia corretta.
1
Mulderig, Andrew J. "Performance and Active Layer Morphology of P3HT-PCPDTBT Organic Photovoltaic Cells". University of Cincinnati / OhioLINK, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1457619609.
Testo completo
2
Yu, Fei. "Graphene-enhanced Polymer Bulk-heterojunction Solar Cells". University of Cincinnati / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=ucin1439310775.
Testo completo
3
Xu, Yifan. "Studies on field effect transistors with conjugated polymer and high permittivity gate dielectrics using pulsed plasma polymerization". Connect to resource, 2005. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1124219179.
Testo completoAbstract (sommario):
Thesis (Ph. D.)--Ohio State University, 2005.Title from first page of PDF file. Document formatted into pages; contains xx, 187 p.; also includes graphics (some col.). Includes bibliographical references (p. 174-187). Available online via OhioLINK's ETD Center
4
Agumba, John O. [Verfasser], e Günter [Akademischer Betreuer] Reiter. "Formation and optical characterization of single crystals of poly(3-hexylthiophene)(P3HT), a model conjugated polymer". Freiburg : Universität, 2016. http://d-nb.info/1119717477/34.
Testo completo
5
Livingstone, Veronica Jean. "One-Pot In-Situ Synthesis of Conductive Polymer/Metal Oxide Composites". University of Toledo / OhioLINK, 2020. http://rave.ohiolink.edu/etdc/view?acc_num=toledo158860469194691.
Testo completo
6
Wang, Wenfeng. "Investigation of Energy Alignment Models at Polymer Interfaces". Scholar Commons, 2014. https://scholarcommons.usf.edu/etd/5148.
Testo completoAbstract (sommario):
The presented study investigated the Induced Density of Interface States (IDIS) model at different polymer interfaces by using photoemission spectroscopy in combination with electrospray deposition.
In recent years, organic electronics have attracted considerable attention due to their advantages of low-cost and easy-fabrication. The performance of such devices crucially depends on the energy barrier that controls the interface charge transfer. A significant effort has been made to explore the mechanisms that determine the direction and magnitude of charge transfer barriers in these devices. As a result of this effort, the IDIS model was developed to predict the energy alignment at metal/organic and organic/organic interfaces. The validity of the IDIS model on molecular interfaces was confirmed by the results of a series of experiments with small molecular materials, which are in good agreement with the theoretical calculations from the IDIS model. The charge neutrality level (CNL) and screening factor for various organic materials can be determined from the linear correlation between the hole injection barrier at metal/organic interface and the work function of its corresponding metal substrate, which stands as one of the most important features of the IDIS model.
The study presented here explores whether the IDIS model is also valid for polymer interfaces. Two prototypical polymer materials: poly(3-hexylthiophene) (P3HT) and poly[2-methoxy-5-(2'-ethylhexyloxy)-p-phenylene vinylene] (MEH-PPV) were selected for the investigation. In the first part of this study, a series of metal/polymer interfaces were prepared using electrospray and investigated with photoemission
spectroscopy. The linear relationship between the hole barriers extracted from the metal/polymer interface and the work function of its respective metal substrate suggests that the IDIS model is also valid for metal/polymer interfaces. The CNLs and the screening factors of P3HT and MEH-PPV are determined respectively. The experiment results are also discussed with regard to the Integer Charge Transfer (ICT) model. The comparison between the two models suggests that the IDIS model should be applied to interfaces prepared in vacuum while the ICT model works on interfaces with an ambient contamination layer present. The second part of the dissertation discusses the photoemission results of the MEH-PPV/P3HT heterojunction from the perspectives of the two models. The results indicate that the IDIS model is valid for polymer/polymer heterojunctions. The IDIS model more accurately predicted the measured orbital line up by using its principles for organic/organic heterojunction than the ICT model.
7
Hon, Sherman Siu-Man. "Calcium vapour deposition on semiconducting polymers studied by adsorption calorimetry and visible light absorption". Thesis, University of British Columbia, 2007. http://hdl.handle.net/2429/863.
Testo completoAbstract (sommario):
A novel UHV microcalorimeter has been used to study the interaction between
calcium and three polymers: MEH-PPV, MEH-PPP and P3HT. All three polymers
behave differently in their reaction kinetics with calcium. On MEH-PPV we measure
45 μJ/cm² of heat generated in excess of the heat of bulk metal growth, 120 μJ/cm²
for MEH-PPP, and 100 μJ/cm² for P3HT. Comparison of the MEH-PPV and MEHPPP
data indicate that the initial reaction of calcium with MEH-PPV occurs at the
vinylene group. We propose, based on hypothetical models, that calcium reacts with
the vinylene groups of MEH-PPV with a reaction heat of 360 kJ/mol and at a
projected surface density of 1.7 sites/nm², while it reacts with the phenylene groups
of MEH-PPP in a two-step process with reaction heats of 200 and 360 kJ/mol
respectively, at a projected surface density of 3.5 sites/nm².
Optical absorption experiments, using either a 1.85 eV diode laser or a xenon lamp
coupled to a scanning monochromator, have also been performed using the same
calorimeter sensor. In the case of MEH-PPV, using the laser we find an optical
absorption cross-section of 3E-¹⁷ cm² per incident calcium atom at low coverages.
The change in absorptance at higher coverages correlates perfectly with the
population of reacted Ca atoms determined calorimetrically. The size of the
absorbance cross-section, and its position just within the band gap of the polymer, are
consistent with the reaction being one of polaron formation. Calcium does not appear
to dope P3HT, while the photon energy range of 1.5 to 3.75 eV used in these
experiments is likely too small for probing polaronic energy states in MEH-PPP.
8
Zellmeier, Matthias. "Characterization of hybrid solar cells prepared from poly-thiophenes and silicon". Doctoral thesis, Humboldt-Universität zu Berlin, Mathematisch-Naturwissenschaftliche Fakultät, 2016. http://dx.doi.org/10.18452/17666.
Testo completoAbstract (sommario):
Das Hauptaugenmerk dieser Arbeit liegt auf der Entwicklung einer Hybridsolarzelle, in der der anorganische Halbleiter Silizium, das organische Polymer und das Kontaktsystem so aufeinander abgestimmt sind, dass ihre Kombination zu einem Bauelement mit hohem Wirkungsgrad führt. Um dieses Ziel zu erreichen wurden verschiedene Maßnahmen ergriffen. Neue Polymermaterialien, abgeleitet von dem prototypischen organischen Halbleiter poly(3-hexylthiophen 2,5 diyl) (P3HT), namentlich poly(3-[3,6-dioxaheptyl]-thiophen) (P3DOT) und poly(3-[2,5,8-trioxanonyl]-thiophen) (P3TOT), wurden umfassend hinsichtlich ihrer Struktur untersucht. Poly thiophen/c-Si hybride Solarzellen, hergestellt aus diesen neuen Polymeren, erreichten Effizienzen bis zu 11 %. Die vollständigen Banddiagramme dieser Poly thiophen/c-Si Hybridgrenzflächen wurden mittels Photoelektronenspektroskopie aufgenommen. Außerdem wurde der Einfluss des Kontaktsystems auf die darunter liegenden Schichten mittels Oberflächenspannungsspektroskopie untersucht. Das Resultat dieser Messungen weißt eine Inversionslage unter der Siliziumoberfläche nach, die sich aufgrund des verwendeten semitransparenten Metallkontaktes formt. Dadurch lassen sich diese Bauteile als MIS Inversionsschicht Solarzelle kategorisieren. Um die Hybridsolarzellen weiter zu verbessern, wurde versucht den semitransparenten Metallkontakt durch Graphen zu ersetzen. Das Graphen wurde durch einen CVD-Prozess gewachsen und erreichte eine laterale Ausdehnung von bis zu 1 cm2. Der Übertrag auf die Solarzelle erfolgte mittels eines Wasser und Zerstörungsfreiem Transferprozess. Trotz dem erfolgreichen Aufbringen des Graphen limitierte ein geringer Füllfaktor aufgrund der geringen Ladungsträgerdichte im Graphen den Wirkungsgrad der Solarzelle. In einem letzten Schritt wurde das Polymer P3HT zum ersten Mal mit polykristallinen Siliziumabsorbern kombiniert. Die invertierte Zellstruktur, die hierbei zu Anwendung kam, erhöhte die Lebensdauer der Solarzelle erheblich.The scope of this thesis was the development of a hybrid solar cell based on silicon in which the inorganic semiconductor, the organic polymer and the contact system are combined in such a manner to result in a photovoltaic device with high power conversion efficiency. To reach this goal several measures were taken. New polymer materials derived from the prototypical organic semiconductor poly(3-hexylthiophene 2,5 diyl) (P3HT), namely poly(3-[3,6-dioxaheptyl]-thiophene) (P3DOT) and poly(3-[2,5,8-trioxanonyl]-thiophene) (P3TOT), were extensively characterized regarding its structural properties. Poly thiophene/c-Si hybrid solar cells fabricated from these new polymers exhibited power conversion efficiencies up to 11 %. The energy level alignment of these poly thiophene/c Si hybrid interfaces was studied using photoelectron spectroscopy. Furthermore, the influence of the contact system on the underlying wafer is investigated with surface photovoltage measurements. The measurements revealed the formation of an inversion layer beneath the silicon surface due to the semitransparent metal contact used in the devices. Therefore, these devices can be classified as MIS inversion layer solar cells. To further improve the hybrid poly thiophene/c-Si solar cells by substituting the semitransparent metal contact, graphene was implemented in the device design as a transparent front contact. The CVD grown graphene sheet had a lateral size of up to 1 cm2 and was applied onto the solar cell using a non-destructive and water-free transfer process. However, despite the successful transfer the power conversion efficiency was restricted by the low fill factor due to a low charge carrier density in the graphene. As a last step, hybrid solar cells in the combination P3HT/polycrystalline silicon absorbers on glass were fabricated for the first time. The inverted device structure used for these solar cells proved beneficial for the lifetime. These devices were stable for up to 3 months.
9
Chapa, Garza Jose L. "A Comparative Study of the Morphology of Flow and Spin Coated P3HT:PCBM Films". University of Akron / OhioLINK, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=akron1374520548.
Testo completo
10
Aiyar, Avishek R. "Understanding the impact of polymer self-organization on the microstructure and charge transport in poly(3-hexylthiophene)". Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/43574.
Testo completoAbstract (sommario):
Conjugated polymers represent the next generation of conducting materials that will enable technological devices incorporating thin film transistors, photovoltaic cells etc., in a cost-effective roll-to-roll manner. Given the importance of microstructure on charge transport, ordered self-assembly in polymeric semiconductors assumes paramount relevance. This thesis thus focuses on a fundamental investigation of the correlations between the morphology and microstructure of the first high mobility solution processable semiconducting polymer, poly(3-hexylthiophene)(P3HT), and its corresponding charge transport properties. The evolution of polymer chain conformations is first studied, leading up to the formation of the conducting channel. An intermediate lyotropic liquid crystalline phase is identified, characterized by anisotropic ordering of the polymer chains. Methods for tuning the microstructure of P3HT thin films are also discussed, with an emphasis on understanding the role of molecular parameters, such as regioregularity and process parameters such as the film formation method. An ultrasound based technique for inducing the formation of ordered π-stacked molecular aggregates is also introduced. The results presented here not only provide understanding of microstructure-charge transport correlations, but also the very process of film formation in solution processable organic semiconductors, which could in turn hold the key to approaching the mobility benchmark represented by single crystals.
11
Olson, Grant T. "Improving Hybrid Solar Cells: Overcoming Charge Extraction Issues In Bulk Mixtures of Polythiophenes and Zinc Oxide Nanostructures". DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1257.
Testo completoAbstract (sommario):
Organic photovoltaics (OPVs) have received a great deal of focus in recent years as a possible alternative to expensive silicon based solar technology. Current challenges for organic photovoltaics are centered around improving their lifetimes and increasing their power conversion efficiencies. One approach to improving the lifetime of such devices has been the inclusion of inorganic metal oxide layers, but interaction between the metal oxides and common conjugated polymers is not favorable. Here we present two methods by which the interactions between polythiophenes and nanostructured ZnO can be made to be more favorable. Using the first method, direct side on attachment of polythiophene to ZnO nanowires via chemical grafting, we demonstrate chemical linkage between the polymer and ZnO phases. The attachment was confirmed to affect the morphological properties of the polymer layer as well, inducing highly ordered regions of the polymer at the ZnO surface via chemical attachment and physical adsorption. Using the second method to improve polythiophene ZnO interactions, we have functionalized ZnO nanowires with organic molecules that favorably interact with conjugated polymer and organic solvents. Photovoltaic devices were made using a blended active layer of functionalized ZnO nanowires and P3HT. Electrical analysis of the resultant devices concluded that the devices were functional photovoltaic cells and isolated the dominant loss mechanisms for further device improvement.
12
Maciel, Alexandre de Castro. "Fabricação e estudo das propriedades de transporte de transistores de filmes finos orgânicos". Universidade de São Paulo, 2012. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-18122012-114317/.
Testo completoAbstract (sommario):
A eletrônica digital desempenha papel essencial no desenvolvimento e manutenção dos padrões de vida em prática hoje no mundo. A peça fundamental para a criação desta era tecnológica é sem dúvidas o transistor. Com o advento de novos materiais, a busca por transistores que oferecem novas oportunidades de processamento e aplicação permitiu que uma nova área fosse criada: a eletrônica orgânica. Transistores de efeito de campo baseados em filmes finos de materiais orgânicos têm recebido grande atenção nas últimas décadas. Apresentamos um estudo experimental e teórico de transistores de efeito de campo a base de filmes finos orgânicos. Foram caracterizados transistores usando um derivado do pentaceno (TMTES-pentaceno) como camada ativa em um dispositivo feito sobre Si/SiO2. Mostramos que a inclusão do semicondutor orgânico em uma matriz polimérica isolante ajuda a manter a estabilidade termo mecânica do dispositivo. Foi desenvolvido um modelo que levasse em conta as resistências parasíticas para explicar o comportamento do transistor em função da temperatura. Também foram construídos e caracterizados transistores usando rr-P3HT como semicondutor e PMMA como isolantes. Apresentamos transistores do tipo Top-Gate e Bottom-Gate com mobilidade máxima de 7 x 10-3 cm2/V.s. Valores de razão ON/OFF de ~ 900 foram encontrados nos transistores otimizados. O comportamento dos transistores é analisado em função da temperatura e os modelos de aproximação de canal gradual e de Vissenberg-Matters foram aplicados para extração dos parâmetros de interesse. Por fim, apresentamos um modelo de corrente de canal baseado na resolução 2D numérica da equação de Poisson usando as idéias de Vissenberg-Matters para a concentração de cargas em função do potencial local. O modelo, embora ainda nos primeiros estágios de desenvolvimento, prevê a saturação da corrente nas curvas de saída simuladas sem limitações de regime de validade.Digital electronics plays an essential role in the development and maintenance of living standards into practice in the world today. The cornerstone for the creation of this technological age is undoubtedly the transistor. With the advent of new materials, the search for transistors that offer new opportunities in processing and application allowed a new area to be created: the organic electronics. Field effect transistors based on organic thin films have received great attention in recent decades. We report an experimental and theoretical study of field effect transistors based on organic thin films. We characterized transistors manufactured using a derivative of pentacene (TMTES-pentacene) as the active layer in a device and using Si/SiO2 as gate and insulator. We show that the inclusion of the organic semiconductor in an insulating polymeric matrix helps to maintain the termo-mechanical stability of the device. A model was developed that take into account the parasitic resistances and to explain the behavior of the transistor as a function of temperature. We also present the manufacturing and characterization process of transistors using rr-P3HT as semiconductor and PMMA as insulator. We report Top-Gate and Bottom-Gate transistors with maximum mobility of 7 x 10-3 cm2/V.s. The maximun ON/OFF ratio of ~ 900 was found for the optimized transistors. The behavior of the transistors was analyzed as a function of temperature and both gradual channel approximation and Vissenberg-Matters models were applied for extracting the parameters. Finally, we present a channel current model based on the resolution of 2D numerical Poisson equation using the ideas of Vissenberg-Matters to the calculate the concentration of charges due to the local potential. The model, although still in the early stages of development, predicts the saturation current at output simulated curves with no limitation of regime validity.
13
Bump, Buddy J. "Synthesis and Characterization of CdSe/ZnS Core/Shell Quantum Dot Sensitized PCPDTBT-P3HT:PCBM Organic Photovoltaics". DigitalCommons@CalPoly, 2014. https://digitalcommons.calpoly.edu/theses/1309.
Testo completoAbstract (sommario):
Durable, cheap, and lightweight polymer based solar cells are needed, if simply to meet the demand for decentralized electrical power production in traditionally “off-grid” areas. Using a blend of Poly(3-hexylthiophene-2,5-diyl) (P3HT), Phenyl-C61-butyric acid methyl ester (PCBM), and the low band-gap polymer Poly[2,6-(4,4-bis-(2- ethylhexyl)-4H-cyclopenta [2,1-b;3,4-b′]dithiophene)-alt-4,7(2,1,3-benzothiadiazole)] (PCPDTBT), we have fabricated devices with a wide spectral response and 3% power conversion efficiency in AM 1.5 conditions; however, this thin film system exhibits only 0.43 optical density at 500 nm. To improve the performance of this polymer blend photovoltaic, we aim to increase absorption by adding CdSe(ZnS) core (shell) quantum dots. Four groups of devices are fabricated: a control group with an active polymer layer of 16 mg/mL P3HT, 16 mg/mL PCBM, and 4 mg/mL PCPDTBT; and three groups with dispersed quantum dots at 4 mg/ml, 1 mg/mL, and 0.25 mg/mL. The (CdSe)ZnS quantum dots are coated with octadecylamine ligands and have a peak absorbance at 560 nm and peak emission at 577 nm. The active layer was dissolved in chlorobenzene solvent and spun on glass substrates, patterned with indium tin oxide. The devices were then annealed for fifteen minutes at 110° C, 140° C, and 170° C. Current-voltage characteristic curves v and optical density data were taken before and after the anneal step. Finally, surface characterization was conducted with atomic force microscopy and electrostatic force microscopy. When compared to the control, the sensitized devices exhibited increased absorption and depressed electrical performance with increasing quantum dot loading. The surface morphology, both electrical and physical, showed deviation from the typical values and patterns shown by the control that increased with quantum dot loading. When the degrading electrical characteristics, increasing optical absorbance, and surface changes, are considered together, it becomes likely that the quantum dots interact in a significant manner with the morphology of the P3HT phase, which leads to an overall decrease in performance.
14
Huq, Abul Fatha Md Anisul. "Interfacial and Solvent Processing Control of Phenyl-C61-Butyric Acid Methyl Ester (PCBM) Incorporated Polymer Thin Films". University of Akron / OhioLINK, 2015. http://rave.ohiolink.edu/etdc/view?acc_num=akron1427746818.
Testo completo
15
Chiu, Yu-Jui. "Wet Organic Field Effect Transistor as DNA sensor". Thesis, Linköping University, The Department of Physics, Chemistry and Biology, 2008. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-11761.
Testo completoAbstract (sommario):
Label-free detection of DNA has been successfully demonstrated on field effect transistor (FET) based devices. Since conducting organic materials was discovered and have attracted more and more research efforts by their profound advantages, this work will focus on utilizing an organic field effect transistor (OFET) as DNA sensor.
An OFET constructed with a transporting fluidic channel, WetOFET, forms a fluid-polymer (active layer) interface where the probe DNA can be introduced. DNA hybridization and non-hybridization after injecting target DNA and non-target DNA were monitored by transistor characteristics. The Hysteresis area of transfer curve increased after DNA hybridization which may be caused by the increasing electrostatic screening induced by the increasing negative charge from target DNA. The different morphology of coating surface could also influence the OFET response.
16
Baughman, Jessi Alan. "Solid-State NMR Characterization of the Structure and Morphology of Bulk Heterojunction Solar Cells". University of Akron / OhioLINK, 2012. http://rave.ohiolink.edu/etdc/view?acc_num=akron1343136219.
Testo completo
17
Alet, Pierre-Jean. "Cellules photovoltaïques en couches minces à base de silicium nanostructuré et de polymère semiconducteur". Palaiseau, Ecole polytechnique, 2008. http://www.theses.fr/2008EPXX0055.
Testo completoAbstract (sommario):
Cette thèse présente un travail exploratoire sur des cellules solaires hybrides, basées sur un matériau inorganique (le silicium) et un polymère (le P3HT). Cette structure a été imaginée pour améliorer les cellules à bas coûts à base de matériaux organiques. Nous démontrons ici sa faisabilité expérimentale et analysons son fonctionnement. L'hétérojonction entre le silicium et le P3HT a été étudiée sur des dispositifs en bicouches planes. Nous montrons qu'elle fournit de l'énergie électrique et que les deux matériaux peuvent contribuer au photocourant. Des rendements de 1,6 % ont été obtenus. Un effort constant a été fait pour simplifier et fiabiliser les procédés de fabrication. Deux nouveaux types de silicium nano-structuré ont été développés. Des ``nano-éponges'', dont la taille typique des pores est de 20 nm, ont été obtenues à l'aide de catalyseurs métalliques par dépôts assistés par plasma à 175 °C. Des nanofils de silicium ont été formés par un procédé inédit : les substrats sont des oxydes transparents conducteurs, les catalyseurs sont générés in situ et la température de croissance est inférieure à 300 °C. La phase würtzite a été mise en évidence dans certains fils, et divers modes de croissance ont été observés. Ces deux nouveaux types de couches minces pourront aussi être utilisées dans des cellules solaires inorganiquesThis thesis presents an exploratory work on a new design of hybrid solar cells, which are based on a junction between an inorganic material (silicon) and a polymer (P3HT). This structure is intended to improve the efficiency of organic based solar cells while maintaining low costs. Here, we investigate its experimental feasibility, and we analyze its performance. The hetero-junction between silicon and P3HT has been studied on bilayer devices. We have shown that this junction generates electrical power under illumination, and that both silicon and P3HT can contribute to the photocurrent. Power conversion efficiencies up to 1. 6% have been obtained. A large amount of work has been done to simplify the fabrication process and to improve its reliability. Two new nano-structured silicon layers have been developed. “Nanosponge” layers, where the typical dimension of pores is 20nm, have been obtained by metal-catalyzed plasma-enhanced CVD at 175C°. Silicon nanowires have been grown by a completely new process: the substrates are transparent conductive oxides, the catalysts are generated in situ, and the growth temperature is below 300C°. The würtzite (Si-IV) phase has been identified in some wires, and various growth modes are observed. Both kinds of layers may also find applications in inorganic solar cells
18
Sfuncia, Gianfranco. "Preparation and Characterization of Single Walled Carbon Nanotubes Poly(3-hexylthiophene) Nanohybrids". Doctoral thesis, Università di Catania, 2014. http://hdl.handle.net/10761/1520.
Testo completoAbstract (sommario):
In this work a purification method for carbon nanotubes was first developed. Purified nanotubes were characterized by AFM, TGA, RAMAN, NIR-PL and then used to prepare composite materials in conjunction with semiconducting polymers. Electrical and optical properties of this composite material were investigated and finally a nanostructuring technique able to create thin hybrid films with nanoscale phase separation was developed.
19
Yang, Lei. "Hole Transport Materials for Solid-State Mesoscopic Solar Cells". Doctoral thesis, Uppsala universitet, Fysikalisk kemi, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:uu:diva-232271.
Testo completoAbstract (sommario):
The solid-state mesoscopic solar cells (sMSCs) have been developed as a promising alternative technology to the conventional photovoltaics. However, the device performance suffers from the low hole-mobilities and the incomplete pore filling of the hole transport materials (HTMs) into the mesoporous electrodes. A variety of HTMs and different preparation methods have been studied to overcome these limitations. There are two types of sMSCs included in this doctoral thesis, namely solid-state dye-sensitized solar cells (sDSCs) and organometallic halide perovskite based solar cells. Two different types of HTMs, namely the small molecule organic HTM spiro-OMeTAD and the conjugated polymer HTM P3HT, were compared in sDSCs. The photo-induced absorption spectroscopy (PIA) spectra and spectroelectrochemical data suggested that the dye-dye hole conduction occurs in the absence of HTM and appears to be of significant importance to the contribution of hole transport. The PIA measurements and transient absorption spectroscopy (TAS) indicated that the oxidized dye was efficiently regenerated by a small molecule organic HTM TPAA due to its excellent pore filling. The conducting polymer P3HT was employed as a co-HTM to transfer the holes away from TPAA to prohibit the charge carrier recombination and to improve the hole transport. An alternative small molecule organic HTM, MeO-TPD, was found to outperform spiro-OMeTAD in sDSCs due to its more efficient pore filling and higher hole-mobility. Moreover, an initial light soaking treatment was observed to significantly improve the device performance due to a mechanism of Li+ ion migration towards the TiO2 surface. In order to overcome the infiltration difficulty of conducting polymer HTMs, a state-of-the-art method to perform in-situ photoelectrochemical polymerization (PEP) in an aqueous micellar solution of bis-EDOT monomer was developed as an environmental-friendly alternative pathway with scale-up potential for constructing efficient sDSCs with polymer HTMs. Three different types of HTMs, namely DEH, spiro-OMeTAD and P3HT, were used to investigate the influence of HTMs on the charge recombination in CH3NH3PbI3 perovskite based sMSCs. The photovoltage decay measurements indicate that the electron lifetime (τn) of these devices decreases by one order of magnitude in the sequence τspiro-OMeTAD > τP3HT > τDEH.
20
Skrypnychuk, Vasyl. "Vertical charge transport in conjugated polymers". Doctoral thesis, Umeå universitet, Institutionen för fysik, 2017. http://urn.kb.se/resolve?urn=urn:nbn:se:umu:diva-133180.
Testo completoAbstract (sommario):
Conjugated polymers are novel organic electronic materials highly important for organic photovoltaic applications. Charge transport is one of the key properties which defines the performance of conjugated polymers in electronic devices. This work aims to explore the charge transport anisotropy in thin films of P3HT, one of the most common conjugated polymers. Using X-ray diffraction techniques and charge transport measurements, the relation between vertical charge transport through thin P3HT films and structure of the films was established. It was shown that particular orientations of crystalline domains of P3HT, namely face-on and chain-on, are beneficial for vertical charge transport. These orientations provide the efficient pathways for the charges to be transported vertically, either via π-π stacking interaction between the adjacent conjugated chains, or via the conjugated chain backbones. It was also demonstrated that particular orientations of crystallites are favourable for the formation of interconnected percolated pathways providing enhanced vertical charge transport across the film. Deposition of P3HT on most commonly used silicon substrates typically results in the formation of mostly edge-on orientation of crystallites which is unfavourable for vertical charge transport. Nanoimprint lithography was demonstrated as a powerful processing method for reorienting the edge-on crystalline domains of P3HT into chain-on (vertical) orientation. It is also shown that thin P3HT films with preferentially face-on orientations of crystallites can be deposited on graphene surface by spin coating. Using patterning of thin P3HT films by nanoimprint lithography, unprecedentedly high average vertical mobilities in the range of 3.1-10.6 cm2 V-1 s-1 were achieved in undoped P3HT. These results demonstrate that charge transport in thin films of a relatively simple and well-known conjugated polymer P3HT can be significantly improved using optimization of crystallinity,orientation of crystallites, polymer chain orientation and alignment in the films.
21
Stinson, Jelynn A. "The Electroanalytical Performance of Sonogel Carbon Titanium (IV) Oxide Electrodes versus Conducting Polymer Electrodes in the Electrochemical Detection of Biological Molecules". Wright State University / OhioLINK, 2007. http://rave.ohiolink.edu/etdc/view?acc_num=wright1181068417.
Testo completo
22
Cunha, Giovanni Paro da. "Estudo da microestrutura e dinâmica molecular do Poly(3-(2\'-ethylhexyl)thiophene)(P3EHT) via ressonância magnética nuclear". Universidade de São Paulo, 2016. http://www.teses.usp.br/teses/disponiveis/76/76132/tde-17052016-093742/.
Testo completoAbstract (sommario):
O estudo da microestrutura e dinâmica molecular de polímeros conjugados é de grande importância para o entendimento das propriedades físicas desta classe de materiais. No presente trabalho utilizou-se técnicas de ressonância magnética nuclear em baixo e alto campo para elucidar os processos de dinâmica molecular e cristalização do polímero Poly(3-(2’-ethylhexyl)thiophene) - P3EHT. O P3EHT é um polímero modelo para tal estudo, pois apresenta temperatura de fusão bem inferior a sua temperatura de degradação. Esta característica permite acompanhar os processos de cristalização in situ utilizando RMN. Além disso, sua similaridade ao já popular P3HT o torna um importante candidato a camada ativa em dispositivos eletrônicos orgânicos. O completo assinalamento do espectro de 13C para o P3EHT foi realizado utilizando as técnicas de defasamento dipolar e HETCOR. Os processos de dinâmica molecular, por sua vez, foram sondados utilizando DIPSHIFT. Observou-se um gradiente de mobilidade na cadeia lateral do polímero. Além disso, os baixos valores de parametros de ordem obtidos em comparação a experimentos similares realizados no P3HT na literatura indicam um aparente aumento no volume livre entre cadeias consecutivas na fase cristalina. Isso indica que a presença do grupo etil adicional no P3EHT causa um completo rearranjo das moléculas e dificulta seu empacotamento. Constatou-se ainda pouca variação das curvas de DIPSHIFT para os carbonos da cadeia lateral como função do método de excitação utilizado, o que aponta para um polímero que apresenta cadeia lateral móvel mesmo em sua fase cristalina. Os dados de dinâmica molecular foram corroborados por medidas de T1, T1ρ e TCH. Utilizando filtros dipolares em baixo campo observou-se três temperaturas de transição para o P3EHT: 250 K, 325 K e 350 K. A cristalização desse material é um processo lento. Verificou-se que o mesmo pode se estender por até até 24h a temperatura ambiente. Mudanças no espectro de 13C utilizando CPMAS em alto campo indicam um ordenamento dos anéis tiofeno (empacotamento π – π) como o principal processo de cristalização para o P3EHT.The study of the microstructure and molecular mobility of conjugated polymers is of the utmost importance for the understanding of the physical properties of this class of materials. In the current work we employed nuclear magnetic resonance techniques to shed light into the processes of molecular dynamics and crystallization of the polymer Poly(3-(2’-ethylhexyl)thiophene) - P3EHT. The P3EHT is a model polymer for such a study since it displays a melting temperature well below it’s degradation temperature, this allowed us to probe the crystallization process in situ using NMR. Furthermore it’s similarity to the already popular P3HT makes it a good candidate to active layer in organic electronic devices. A complete assignment of the 13C spectrum was achieved for the P3EHT, using the dipolar dephasing and HETCOR techniques. The molecular movements were probed by DIPSHIFT. We observed a mobility gradient along the side-chain of the material. The low values obtained for the order parameter in comparison to similar experiments done on the P3HT on the literature indicate a apparent increase in the free volume between consecutive chains in the crystalline phase, this is a strong indicative that the addition of the ethyl group to the repetitive unit strongly rearranges the molecules, difficulting packing. Moreover the depth of the DIPSHIFT curves for the side-chain carbons at half the rotor period don’t seem to be a function of the excitation method employed, this points to a polymer that is throughout mobile, i.e. that has carbons with a high degree of mobility even in it’s crystalline phase. This results were corroborated by measurements of T1, T1ρ e TCH. Employing dipolar filters at low field three transition temperatures were observed: 250 K, 325 K and 350K. The crystallization of the P3EHT is a slow process. We found that it took up to 24h for the material to fully recrystallize from the melting at room temperature. Changes in the 13C CPMAS spectra at high fields indicate a ordering of the thiophene rings (π – π stacking) as the primary method for the crystallization in the P3EHT.
23
Diarra, Cheick Oumar. "Modélisation par dynamique moléculaire ab initio du transport des excitons et du transport thermique dans les semiconducteurs organiques pour la collecte d'énergie". Electronic Thesis or Diss., Strasbourg, 2024. http://www.theses.fr/2024STRAD013.
Testo completoAbstract (sommario):
L'exciton joue un rôle clé dans le fonctionnement des cellules solaires organiques (OSCs). Comprendre sa dynamique dans les semiconducteurs organiques est essentiel, notamment pour améliorer la longueur de diffusion, une propriété déterminante pour la performance des hétérojonctions planaires, envisagées comme une alternative plus stable aux hétérojonctions en volume (BHJ). Dans la première partie de cette thèse, nous avons développé une approche méthodologique robuste et polyvalente pour évaluer la longueur de diffusion de l'exciton dans les semiconducteurs organiques. Cette approche, basée sur AIMD-ROKS, a été validée avec succès dans le cas du polymère P3HT. Elle a également été appliquée à l'accepteur NFA O-IDTBR, révélant des longueurs de diffusion prometteuses, mais encore insuffisantes pour les hétérojonctions planaires. Dans la deuxième partie de la thèse, le transfert de chaleur dans les semiconducteurs organiques a été exploré, élément crucial pour la performance des dispositifs thermoélectriques. Ces études se sont concentrées sur le P3HT, un matériau utilisé en thermoélectricité. Dans un premier temps, la conductivité thermique au sein des chaînes de P3HT a été étudiée, révélant l'influence de la longueur des chaînes de polymère. Ensuite, les transferts de chaleur entre ces chaînes ont également été examinésThe exciton plays a central role in the functioning of organic solar cells (OSCs). Understanding its dynamics in organic semiconductors is essential, particularly to optimize the diffusion length, a key property for the performance of planar heterojunctions, which are considered as a potentially more stable alternative to bulk heterojunctions (BHJ) in certain contexts. In the first part of this thesis, we developed a robust and versatile methodological approach to evaluate the exciton diffusion length in organic semiconductors. This method, based on AIMD-ROKS, was successfully validated for the P3HT polymer. It was also applied to the NFA O-IDTBR acceptor, revealing promising diffusion lengths, though still insufficient for planar heterojunctions. The second part of the thesis explores heat transfer in organic semiconductors, a crucial element for the performance of thermoelectric devices. These studies focused on P3HT, a material used in thermoelectricity. First, the thermal conductivity within P3HT chains was studied, revealing the influence of polymer chain length. Then, heat transfers between these chains were also examined
24
Sharma, Kartikeya. "Structural modifications of polyester fibres induced by thermal and chemical treatments to obtain high-performance fibres". Thesis, KTH, Fiber- och polymerteknologi, 2021. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-296254.
Testo completoAbstract (sommario):
Del A: Polyetylentereftalat fibrer I detta arbete presenteras olika metoder för att framställa monofilament av polyetylentereftalat (PET) (diameter: 30-50 µm) med en radiell gradient. Nyutvecklad Raman-spektroskopiteknik har använts för att kartlägga dessa inducerade radiella gradienter i t.ex. kristallinitet. På liknande sätt har FTIR-ATR teknik modifierats och anpassats för att studera ytegenskaperna hos dessa filament. Industriella filamentprover och egna smältspunna PET-filament har framgångsrikt modifierats med användning av olika termiska och kemiska behandlingar för att erhålla fibrer med förbättrade mekaniska egenskaper och minskad fibrillering. De strukturella förändringar som uppträdde i filamenten på mikroskopisk nivå karakteriserades med bl a infraröd analys, termisk analys, Raman-mikroskopi och röntgenteknik (SAXS och WAXD). Tester av fibrilleringsegenskaper utfördes av industriella partners med egenutvecklad teknik följt av testning av masterbatch-fibrer på en vävningssimulator. Resultaten i laboratorieskala avslöjade fibrernas strukturella anisotropi och radiella gradienter, vilka visade en minskad fibrillering med en viss inverkan på de mekaniska egenskaperna. Del B: Poly(3-hydroxybutyrat) fibrer Detta arbete presenterar studier av poly(3-hydroxybutyrat) (P3HB) fibrer med reversibla strukturförändringar. Tidigare studier har visat att kristallisationen hos P3HB fibrer i huvudsakligen sker i ortorombisk α-kristallform. Stress-anlöpning resulterar dock i en förändring i beteendet hos P3HB-materialet. Strukturen hos P3HB fibrer består av amorfa och kristallina regioner samt en mesofas. Mesofasen antas vara belägen mellan α-kristallerna och uppträder som starkt orienterade bindningskedjor, s k “tie-chains”. Denna studie syftar till att observera effekten av stress-anlöpning på mesofasen och dess beroende av anlöpningsförhållandena. Förändringarna i mesofasen observeras med en anpassad och polariserad Attenuated Total Reflection Fourier Transform Infrared Spectroscopy (ATR-FTIR) samt med Differential Scanning Calorimetry (DSC). Resultaten från ATR-FTIR visar att mesofasen är närvarande i spunna och högt stress-anlöpta fibrer, medan den är frånvarande i fibrer som är lågt stress-anlöpta. Mesofasen kan emellertid återupptas i lågt stress-anlöpta fibrer genom dragning. In situ ATR-FTIR användes för att studera förändringarna i materialbeteendet under en dragningsprocess för att observera periodiciteten i förekomsten av mesofasen. Det visade sig att förekomsten av mesofasen är en starkt reversibel process som observeras som en funktion av topparnas intensitet i ATR-FTIR.Part A: Poly(ethylene terephthalate) fibres In this work, various methods to produce Poly(ethylene terephthalate) (PET) monofilaments (diameter: 30-50µm) with a radial gradient are presented along with a newly developed Raman spectroscopy technique to map these induced radial gradients in e.g. crystallinity. On similar lines, FTIR-ATR technique has been modified and adapted to study the surface properties of these fine filaments. Industrial filament samples and in-house melt-spun PET filaments have been successfully modified using various thermal and chemical treatments to obtain fibres with improved mechanical properties and reduced fibrillation. The structural changes occurring in the filaments on the microscopic level were characterized using infrared analysis, thermal analysis, Raman microscopy and X-ray techniques (SAXS and WAXD) among others. The fibrillation properties were tested by the industrial partners using a technique developed in-house followed by testing of masterbatch fibres on a weaving simulator. Lab-scale results revealed the structural anisotropy and radial gradient maps of the fibres which also demonstrated reduced fibrillation with some impact on mechanical properties also being observed. Part B: Poly(3-hydroxybutyrate) fibres This work presents studies on poly(3-hydroxybutyrate) (P3HB) fibres with reversible structural changes. Previously reported literature shows that crystallization of P3HB fibres takes place majorly in the orthorhombic α-crystal form. However, the stress-annealing results in a change of the material behaviour of P3HB. P3HB fibres compose of amorphous regions, crystalline regions and mesophase in their structure. The mesophase is supposed to be located in between the α-crystals of the material as highly oriented tie-chains. This study targets to observe the effect of stress-annealing of the mesophase present in the P3HB fibres and its dependence on the annealing conditions. The changes in the mesophase content are observed with the help of a highly adapted polarized Attenuated Total Reflection Fourier Transform Infrared spectroscopy (ATR-FTIR) and Differential Scanning Calorimetry (DSC). The presented results from polarized ATR-FTIR show that the mesophase is present in as-spun and high stress annealed fibres while it is absent in fibres annealed with low stress. However, the mesophase can be re-obtained in low stress annealed fibres through tensile drawing. In-situ ATR-FTIR was utilized to study the changes in the material behaviour during a tensile drawing process to observe the cyclicity in the occurrence of the mesophase. It was found that the existence of mesophase is a highly reversible process observed as a function of the peak intensities of the polarized ATR-FTIR spectroscopy.
25
Nguyen, Vu Anh. "Blends of Polydioctylfluorene (PFO) with polymeric and monomeric energy acceptors: correlation of fluorescence energy transfer and film morphology in breath figures and films". Diss., Atlanta, Ga. : Georgia Institute of Technology, 2008. http://hdl.handle.net/1853/24609.
Testo completoAbstract (sommario):
Thesis (Ph.D.)--Chemistry and Biochemistry, Georgia Institute of Technology, 2008.Committee Chair: Tolbert, Laren; Committee Member: Collard, David; Committee Member: Lyon, Andrew; Committee Member: Srinivasarao, Mohan; Committee Member: Wilkinson, Angus
26
Vecchiola, Aymeric. "Développement d’une imagerie de résistance électrique locale par AFM à pointe conductrice en mode contact intermittent". Thesis, Paris 11, 2015. http://www.theses.fr/2015PA112058/document.
Testo completoAbstract (sommario):
Le microscope à force atomique (AFM) permet de caractériser avec une excellente résolution spatiale les surfaces d’échantillons de différentes natures et peut être mis en œuvre dans des milieux variés. Cette versatilité a favorisé le développement d’un grand nombre de techniques dérivées, destinées à investiguer diverses propriétés physiques locales. Le LGEP a ainsi réalisé un module, le Résiscope, capable de mesurer la résistance électrique locale à la surface d’un échantillon polarisé en continu, sur une gamme de 11 décades. Mise au point en mode contact, où la pointe exerce en permanence une force sur l’échantillon, cette technique fonctionne très bien sur des matériaux durs, mais trouve ses limites sur des échantillons mous ou fragiles puisque dans certaines conditions, la pointe peut altérer leur surface. Pour de tels échantillons, un mode contact intermittent, dans lequel la pointe vient à intervalles réguliers toucher très brièvement la surface, est plus approprié, mais complique la réalisation des mesures électriques. Le but de la thèse consistait à lever cette difficulté en modifiant le Résiscope pour pouvoir l’associer au « Pulsed Force Mode », mode intermittent où la pointe oscille à une fréquence de 100Hz à 2000Hz.Différentes évolutions matérielles et logicielles ont été apportées pour permettre le suivi temporel détaillé du signal de résistance électrique à chaque établissement/rupture de contact (indispensable pour passer en revue les phénomènes liés à l’intermittence), de même que pour pouvoir travailler à des vitesses de balayage acceptables. Pour l’imagerie, les meilleurs contrastes ont été obtenus grâce à une électronique de synchronisation et de traitement prenant en compte les valeurs de résistance électrique à des moments bien précis. Pour tester ce nouveau système, nous avons dans un premier temps comparé les courbes de résistance et de déflexion que nous obtenons par ce mode avec celles considérées classiquement dans le mode approche-retrait. Nous avons ensuite étudié l’influence des principaux paramètres (fréquence et amplitude d’oscillation, force d’appui, type de pointe, etc.) sur les mesures topographiques et électriques, en utilisant le HOPG comme matériau de référence. Ces essais ont notamment permis de mettre en évidence un retard quasi systématique du signal électrique par rapport au signal de déflexion (autre que le temps de mesure propre au Résiscope), dont nous n’avons pu élucider l’origine. Une fois ces connaissances acquises, nous avons étudié deux types d’échantillons organiques, l’un à caractère académique – des monocouches auto-assemblées d’alcanethiols (SAMs), l’autre à finalité plus applicative – des couches minces formées d’un réseau interpénétré de deux constituants (P3HT:PCBM) destinées aux cellules photovoltaïques. Dans les deux cas nous avons montré la pertinence de l’outil Résiscope en mode intermittent pour obtenir des informations qualitatives et quantitatives. Parallèlement à ces travaux sur matériaux fragiles, nous avons mené une étude annexe sur un phénomène de croissance de matière à caractère isolant constaté dans des conditions particulières sur différents matériaux durs, qui a été interprété comme la formation de polymère de friction sous l’effet des nano-glissements répétés associés à la déflexion du levier.Ces travaux ont été réalisés dans le cadre d’une convention CIFRE avec la société Concept Scientifique Instruments, adossée au projet ANR « MELAMIN » (P2N 2011)The atomic force microscope (AFM) allows to characterize with excellent spatial resolution samples of different types of surfaces and can be implemented in various environments. This versatility has encouraged the development of a large number of derivative technics, intended to investigate various local physical properties. The LGEP thus achieved a module, the Résiscope, capable of measuring the local electrical resistance on the surface of a sample polarized continuously, on a range of 11 decades. Developed in contact mode, where the tip continuously exerts a force on the sample, this technic works well on hard materials, but finds its limits on soft or fragile samples since under certain conditions, the tip can alter the surface. For such samples, an intermittent contact mode, in which the tip comes at regular intervals touch very briefly the surface, is more appropriate, but complicates the achievement of electrical measurements. The aim of this thesis was to overcome this difficulty by changing the Résiscope to be able to join the "Pulsed Force Mode", intermittent mode where the tip oscillates at a frequency of 100Hz to 2000Hz. Different hardware and software changes have been made to permit the detailed temporal monitoring of the electrical resistance signal to each make / break contact (necessary to review the phenomena related to intermittency), as well as to be able to work in acceptable scan speeds. For imaging, the best contrasts were obtained through an electronic timing and treatment taking into account the electrical resistance values at specific times.To test this new system, we have initially compared resistance and deflection curves we get by this mode with those considered classically in the force-distance curves mode. We then investigated the influence of main parameters (frequency and amplitude of oscillation, setpoint, coating of the tips, etc.) on the topographical and electrical measurements, using the HOPG as reference material. These tests resulted to highlight a nearly systematic delay of the electrical signal relative to the deflection signal (other than the Resiscope measure time), which we were not able to elucidate the origin. Once these knowledge acquired, we studied two types of organic samples, one in academic nature - Self-Assembled Monolayers of alkanethiols (SAMs), the other more applicative purpose – formed of thin layers of an interpenetrating network of two components (P3HT:PCBM) for photovoltaic cells. In both cases we have shown the relevance of the Resiscope tool in intermittent mode to obtain qualitative and quantitative information. In addition to these work on fragile materials, we conducted an annex study on a phenomenon of growth material of insulating nature found in special conditions on various hard materials, which has been interpreted as the friction polymer formation as a result of repeatedly nano-sliding associated with the deflection of the cantilever. These investigations were conducted under a CIFRE agreement with the Concept Scientific Instruments company, backed by the ANR MELAMIN» (P2N 2011) project
27
Chen, Po-yu, e 陳柏佑. "P3HT/PCBM/PMMA blended polymer solar cell study". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/99636896502278923581.
Testo completoAbstract (sommario):
碩士明道大學
光電暨能源工程學系碩士班
98
In this study, the P3HT/PCBM active layer was used in an organic solar cell, and then we blended different ratio of the PMMA. A key factor of power efficiency was ratio of the PMMA. The measurement of I-V characteristic curve was performed, in order to calculate the power conversion efficiency of an organic solar cell. When the ratio of P3HT:PCBM:PMMA was 5:4.8:0.2, we could get the best performance power conversion efficiency of solar cell. The open circuit voltage (VOC) was 0.38 V and the short circuit current (JSC) was increased from 4.91 to 10.1(mA/cm2). Finally, the power efficiency is increased from 0.73% to 1.58%.
28
Chen, Dian. "Organic photovoltaics based on P3HT/PCBM: correlating efficiency and morphology". 2011. https://scholarworks.umass.edu/dissertations/AAI3482595.
Testo completoAbstract (sommario):
Controlling the morphology of thin films is key in optimizing the efficiency of polymer-based photovoltaic (PV) devices. The morphology and interfacial behavior of the multicomponent active layers confined between electrodes are strongly influenced by the preparation conditions. Results obtained in this work quantitatively show the photovoltaic device performance is strongly affected by the nanoscopic morphology, crystal orientation, composition distribution and the interdiffusion behavior of the photoactive layer. To better understand the physics of the photoactive layer in the organic photovoltaic devices, it is necessary to gain a quantitative understanding of the morphology and the manner in which it develops. A key element in the kinetics associated with the structure development is the interdiffusion of the components. To that end we used poly(3-hexylthiophene) (P3HT) / [6,6]-phenyl C61-butyric acid methyl ester (PCBM) bilayers as a model to investigate the interdiffusion of the components and its role in the development of the morphology. A detailed description of the diffusion behavior and the morphology developed from a layer of P3HT in contact with a layer of PCBM during thermal annealing is given. Amorphous P3HT and PCBM are shown to be highly miscible and PCBM can penetrate into the P3HT layer through the P3HT amorphous region and form the bulk heterojunction structure within a few second of annealing at 150°C. The results indicated that one phase is a pure P3HT crystal domain and the other phase is the mixture of amorphous P3HT and PCBM, which is not consistent with a phase separation of the components by a spinodal decomposition mechanism. We put forth an alternative mechanism, namely a competitive crystallization/diffusion argument, to describe the origin of the morphology. These findings provide new insights and guidance in the generation of active layers in organic photovoltaics that are crucial in enhancing the device performance. Textured organic solar cells were also studied, providing another route to fabricate higher performance devices.
29
Liu, Tai-Chun, e 劉泰均. "Fluorescence Characterization of Isolated P3HT Polymer Chains by Scanning Near-Field Optics Microscopy". Thesis, 2016. http://ndltd.ncl.edu.tw/handle/37397467466754432508.
Testo completoAbstract (sommario):
碩士國立東華大學
材料科學與工程學系
104
Conjugated polymers are important materials for organic light emitting diodes (OLED) and organic solar cells. The optoelectronic properties are strongly influenced by their chain conformations, inter-chain stacking, and intermolecular aggregations. In this thesis, we investigate the correlation between the morphology and fluorescence property of P3HT (poly (3-hexylthiophene-2,5-diyl)) polymer by both far-field and near-field optical methods. Macroscopically, we use homemade optical microscope to study the fluorescence spectroscopy of liquid and thin film samples prepared at different concentrations. From the surface morphologies revealed by an atomic force microscope (AFM), different areas of stacking aggregations, tangled bundles, and even extended single chains were observed. Not only we could prepare various film morphologies by tuning different preparation conditions but also the corresponding fluorescence spectrum could be obtained. Microscopically, a scanning near-field optical microscope (SNOM) system is utilized to obtain the surface morphology and fluorescence spectroscopy simultaneously. We modified the optical path and feedback controlling system thus successfully enhances the collection efficiency and the stability of the whole system. The optical resolution achieved 60 nm. By these improvements, we can visualize the effect of aggregation size on the fluorescence intensity, peak position, and spectral half width. Generally, stronger fluorescence is observed in larger aggregates. However, bright fluorescence also happens in case of some extended single chains. These results suggest that fluorescence would be reduced by the formation of excimer in the bundle of polymer chains. With the increasing size of aggregation, more polymer chains are presented so that fluorescence intensity increases with aggregation size. The simultaneous measurement of near-field fluorescence and morphology provide microscopic information with great resolution, which is a very important technology for understanding materials for optoelectronic applications.
30
Liu, Hung-Wei, e 劉虹薇. "Thermal stability enhancement of P3HT/PCBM solar cells by controlling the polymer regioregularity". Thesis, 2009. http://ndltd.ncl.edu.tw/handle/y759hj.
Testo completoAbstract (sommario):
碩士國立臺北科技大學
有機高分子研究所
97
Polymer solar cells based on poly(3-hexylthiophene) (P3HT)/[6,6]-phenyl C61 butyric acid methyl ester blends recently have attracted great research interests due to their high energy conversion efficiency. Although the efficiency of these cells can be usually optimized by a thermal annealing process, they are also very sensitive to the environmental temperature. In this study, a series of solar cells with a structure of ITO/PEDOT:PSS/P3HT:PCBM/Al were fabricated by adding a small amount of low-regioregularity P3HT into the P3HT/PCBM blends as photoactive material. After thermal annealing the device at 150OC for 10 min, the thermal stability of the cell was carried out at either 150OC or 90OC. Experimental results indicate that the presence of these low-regioregularity P3HT effectively suppressed the degradation of the cell efficiency upon heating. Furthermore, the morphology and the optical properties of P3HT/PCBM were characterized by OM, TEM, AFM, UV-vis absorption and photoluminescence. All data clearly revealed the low-regioregularity P3HT can greatly lowered the occurrence of macroscopic phase separation between P3HT and PCBM.
31
Lu, Hsuan-Tzu, e 盧宣慈. "Control the Molecular Diffusion of Optically Excited Conjugated Polymer P3HT via Masked Light Absorption". Thesis, 2017. http://ndltd.ncl.edu.tw/handle/an2k4t.
Testo completo
32
張智鴻. "Optoelectronic enhancements by molecular stretching of conjugated polymer P3HT: Local deformation and thin film dewetting". Thesis, 2012. http://ndltd.ncl.edu.tw/handle/53057672509940561826.
Testo completo
33
Lin, Li-Hua, e 林莉華. "Fabrication of template wetted P3HT/PCBM nanorod array structure and applied for polymer heterojunction solar cell devices". Thesis, 2008. http://ndltd.ncl.edu.tw/handle/61167641039224809350.
Testo completoAbstract (sommario):
碩士國立交通大學
材料科學與工程系所
96
In this work, we fabricate the poly (3-hexylthiophene)/[6, 6]-phenyl-C61 butyric acid methyl ester (P3HT/PCBM) nanorod and apply to polymer hetrojunction solar cell device. We utilize the template wetting method to generate the P3HT/PCBM nanorod structure. The processing parameters of nanorod structure which contain solvent effect, wetting time and temperature, and the thickness of the film are investigated. The P3HT/PCBM nanorods reveal the core-shell structure due to the phase separation; this structure can generate a straight pathway for charge transport to both electrodes. Crystallization of P3HT in the P3HT/PCBM nanorods are characterized by the X-ray diffractometer, and the crystallization of P3HT in nanorod structures has been improved. For optical properties, ultraviolet-visible spectroscopy shows that absorption spectrum of P3HT/PCBM nanorods is broadened due to light scattering within the array of nanorods comprising the mat. For device (ITO/PEDOT:PSS/active layer/Al) performance, the aluminum is evaporated into the apertures between rods to rods spaces to provide more contact area between the active layer and the electrode to collect the current efficiently. Finally, the results show more capture of solar spectrum and efficient current collection for device of the nanorod structure which is successfully applied for polymer hetrojunction solar cells
34
Gavvalapalli, Nagarjuna. "Breaking the barriers of all-polymer solar cells: Solving electron transporter and morphology problems". 2012. https://scholarworks.umass.edu/dissertations/AAI3545923.
Testo completoAbstract (sommario):
All-polymer solar cells (APSC) are a class of organic solar cells in which hole and electron transporting phases are made of conjugated polymers. Unlike polymer/fullerene solar cell, photoactive material of APSC can be designed to have hole and electron transporting polymers with complementary absorption range and proper frontier energy level offset. However, the highest reported PCE of APSC is 5 times less than that of polymer/fullerene solar cell. The low PCE of APSC is mainly due to: i) low charge separation efficiency; and ii) lack of optimal morphology to facilitate charge transfer and transport; and iii) lack of control over the exciton and charge transport in each phase. My research work is focused towards addressing these issues. The charge separation efficiency of APSC can be enhanced by designing novel electron transporting polymers with: i) broad absorption range; ii) high electron mobility; and iii) high dielectric constant. In addition to with the above parameters chemical and electronic structure of the repeating unit of conjugated polymer also plays a role in charge separation efficiency. So far only three classes of electron transporting polymers, CN substituted PPV, 2,1,3-benzothiadiazole derived polymers and rylene diimide derived polymers, are used in APSC. Thus to enhance the charge separation efficiency new classes of electron transporting polymers with the above characteristics need to be synthesized. I have developed a new straightforward synthetic strategy to rapidly generate new classes of electron transporting polymers with different chemical and electronic structure, broad absorption range, and high electron mobility from readily available electron deficient monomers. In APSCs due to low entropy of mixing, polymers tend to micro-phase segregate rather than forming the more useful nano-phase segregation. Optimizing the polymer blend morphology to obtain nano-phase segregation is specific to the system under study, time consuming, and not trivial. Thus to avoid micro-phase segregation, nanoparticles of hole and electron transporters are synthesized and blended. But the PCE of nanoparticle blends are far less than those of polymer blends. This is mainly due to the: i) lack of optimal assembly of nanoparticles to facilitate charge transfer and transport processes; and ii) lack of control over the exciton and charge transport properties within the nanoparticles. Polymer packing within the nanoparticle controls the optoelectronic and charge transport properties of the nanoparticle. In this work I have shown that the solvent used to synthesize nanoparticles plays a crucial role in determining the assembly of polymer chains inside the nanoparticle there by affecting its exciton and charge transport processes. To obtain the optimal morphology for better charge transfer and transport, we have also synthesized nanoparticles of different radius with surfactants of opposite charge. We propose that depending on the radius and/or Coulombic interactions these nanoparticles can be assembled into mineral structure-types that are useful for photovoltaic devices.
35
Cheng, Yan-Heng, e 陳彥亨. "Effect of gold nanoparticle buffer layer and Nano Composite Conjugate Polymer on characteristics of P3HT thin film transistors". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/55706768396316306124.
Testo completoAbstract (sommario):
碩士國立中正大學
光機電整合工程所
98
This thesis aims to investigate the effects of gold nanoparticles (Au-NPs) on the performance of organic thin-film transistors (OTFTs). This study is accomplished through two approaches: one is introducing the Au-NPs as a buffer layer, in between the dielectric and the semiconducting layers; and, the other is blending the newly synthesized nanocomposites, P3HT-Au, into the P3HT matrix as the OTFTs’ semiconducting layer. Results show, with introducing the negatively charged Au-NPs buffer layer, the electric field can be enhanced that induces more hole carriers and results in apparent increase in saturated drain currents. Consequently, the devices’ characteristics are effectively improved: the mobility and on/off ratio are increased and the threshold voltage is reduced. On the other hand, the experiments for the second approach show that the blended P3HT-Au can be dispersed uniformly in the P3HT matrix and the drain currents enhance obviously for the devices with the P3HT-Au blending. Here, the energy band diagrams of the polymers of P3HT blending with and without P3HT-Au are measured by the cyclic voltammetry that serve as the theoretical basis for elaborating on the devices’ performance enhancement. Both procedures for fabricating the Au-NPs as the buffer layer and the P3HT-Au in the P3HT matrix are solution processable. They are very straightforward and compatible to the other fabrication steps as well as are executable at room temperature and in the ambient environment. And, most importantly, results demonstrate both approaches can enhance device performance effectively.
36
Wen, Lin Ching, e 林靖文. "Study Suitable Electrode of Polymer Thin Film Transistor (RR-P3HT) and Gate Leakage Current Characteristics on HfO2 Gate Insulator". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/03962575789635396073.
Testo completoAbstract (sommario):
碩士長庚大學
電子工程研究所
95
Abstract The device, based on an organic semiconductor, has the potential to change the display industry and develop one of the technological mainstreams in the future. It has particular possibilities in large area deposition or simple fabrication, mechanical flexibility, low temperature process and especially, and ultra low-cost application. However, the disadvantage of high operation voltage still exists in the practical application of this novel device. In this paper, an organic thin film transistor based on Poly (3-hexlthiophene) (P3HT) with high dielectric constant materials (HfO2) has an advantage in terms of low temperature process and low operation voltage and has successfully been fabricated. In Chapter 2, we find the low carrier mobility in organic thin film transistor with Au/Al as contact metal. Moreover, the on current is always about 2μA. We begin to notice the junction between the metal and semiconductor and choose high work function metal (Au/Cr) as the contact metal. The experimental results support the improvement of the device characteristic, but the crowding effect can still exist. However, we fabricate the device base on purification P3HT with Au/Cr as contact metal. The crowding effect can be improved substantially and promote the device characteristic. In Chapter 3, we investigate the origin of ID off current in our devices. When the quality of oxide is normal, the horizontal direction dominates the leakage current. By patterning the P3HT film, the device performance can be improved. In addition, in the condition wherein the vertical direction dominates the leakage current, the major origin of leakage current is the oxide itself.
37
Chen, Yi-Hao, e 陳逸豪. "Stabilization of Poly(3-hexylthiophene)/PCBM Morphology by Hydroxyl Group End-functionalized P3HT and Its Application to Polymer Solar Cells". Thesis, 2011. http://ndltd.ncl.edu.tw/handle/62805728283734387843.
Testo completoAbstract (sommario):
碩士輔仁大學
化學系
100
Poly(3-hexylthiophene) (P3HT) and [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) are widely used as p-type material and n-type material in polymer solar cells. Phase separation during thermal treatment is observed for the P3HT/PCBM blend because of poor compatibility within these two materials. Severe aggregation of PCBM occurs after thermal treatment and results in inefficient exciton dissociation. A hydroxyl group end-functionalized P3HT (HOC-P3HT-COH) is synthesized as compatibilizer to control morphology of the P3HT/PCBM blend through H-bond formation. Nuclear Magnetic Resonance Spectroscopy (NMR), Infrared Spectrometry (IR), and MALDI-TOF Mass Spectroscopy, and Gel Permeation Chromatography (GPC) are used to characterize HOC-P3HT-COH and also H-bond formation. UV-Vis Spectroscopy, Scanning Electron Microscopy (SEM), Atomic Force Microscopy (AFM), and Optical Microscopy (OM) are conducted to investigate morphology of P3HT/PCBM/HOC-P3HT-COH blend. A 4.06 % PCE polymer cell with improved thermal stability is fabricated with addition of 5 % HOC-P3HT-COH in the P3HT/PCBM blend.
38
Jia-Huang, Lin, e 林佳煌. "Investigation of Structural Materials on Polymer Thin Film Transistor (RR-P3HT) to Improve Threshold Voltage and On/Off Current Ratio". Thesis, 2007. http://ndltd.ncl.edu.tw/handle/81409253449262701944.
Testo completoAbstract (sommario):
碩士長庚大學
光電工程研究所
95
More researches are investigated on organic thin film transistor (OTFT) due to the development of flexible electronics. The polymer thin film transistor has the advantage of its simple process. However, it has some drawbacks such as higher threshold voltage and lower on/off current ratio. These disadvantages limit its applications on circuit. In order to improve the electrical performance, we focus our attentions on the three components of device such as dielectrics, electrodes, and active materials. First, we use Al2O3 and HfO2 as dielectrics. Devices with the dielectric layer of higher dielectric constant lead to lower threshold voltage. Devices with the dielectric of HfO2 have threshold voltage lower than 3V. Next, we try to limit the gate leakage current and to enhance the carrier injection current by using different metals as electrodes in device. We use Al and Al/Au as gate and contact electrodes, respectively. The gate leakage current will be controlled less than 10-8A and the performance of carrier injection current will also be improved. Finally, we choose rr-P3HT dissolved in various solvents, p-xylene, chloroform, and 1,2,4-trichlorobenzene as active materials. We used spin coating system to deposit the rr-P3HT films. The results show that chloroform devices have a lower gate leakage current and the threshold voltage of ~2V, mobility of 3 10-3 cm2/V-s, driving current of 1uA, and the on/off current ratio of 186 can be extracted from measurements.
39
Phuong, Le Anh, e 黎英芳. "The Synthesis and Optoelectronic Behaviour of Conjugated Polymer Poly(3-hexylthiophene) P3HT Grafted on the surface of Multi-Walled Carbon Nanotubes". Thesis, 2010. http://ndltd.ncl.edu.tw/handle/33411214523326824946.
Testo completo
40
Anjaneyulu, Ponnam. "Charge Transport in Semiconducting Polymer Devices". Thesis, 2012. http://etd.iisc.ac.in/handle/2005/3166.
Testo completoAbstract (sommario):
Understanding the fundamentals of Organic semiconductors is crucial aspect towards the technological applications. Conjugated polymers have shown many interesting physical properties. Especially the electronic and optical properties of these materials have great impact on the daily life. Much work has been devoted to gain the knowledge on the electrical and photo physical properties of these materials. Despite the large number of studies in fabrication and characterisation on these devices some of the fundamental properties like charge transport, carrier generation and its control by doping are not well accomplished.
The Thesis consists of 6 chapters. First chapter is a brief introduction on various properties of semiconducting polymers. Different charge transport models and their basic mechanisms are discussed. Chapter 2 discusses the synthesis, device making and experimental methods used to characterise the polymer devices. Chapter 3 is focused on transport properties in polypyrrole devices and its variation with different experimental conditions. Chapter 4 is aimed to understand the anomalies in the current-voltage characteristics appearing in some of the thiophene based devices. In Chapter 5, the impedance measurement technique is used to characterise the poly (3-hexylthiophene) devices and the outcomes are presented and chapter 6 summarises all the experimental results obtained in this thesis work and presents some future aspects and directions.
Chapter 1: Some of the basic properties and recent advancements in the field of organic semiconductors are discussed in this chapter. Organic semiconductor devices based on conjugated polymers are now becoming alternatives to inorganic semiconductors in many fields. Mobility of these conjugated polymers can be increased by adding dopants and also by choosing appropriate metal contacts for charge injection and extraction. The complexity of the metal-polymer interfaces can be better understood by varying the carrier density and studying their transport properties with various experimental tools.
Chapter 2: The polymer films prepared in this study are electrochemically deposited on to various conducting substrates. The doping and de-doping of the carriers is done by passing a current and reversing its polarity for different time intervals. Device structures for the measurements are obtained by making a top contact on top of the polymer layer. The current-voltage (I-V) and impedance measurements are carried out in metal-polymer-metal geometry. Temperature dependent studies down to 10 K were performed in a continuous flow cryostat to understand the role of temperature in transport studies. Impedance and light measurements are also carried out in the same geometry.
Chapter 3: Transport measurements on polypyrrole devices have shown a space-charge limited (SCLC) conduction, which is also known as bulk property of the materials. I-V curves displayed non-ohmic behaviour at higher voltages and by varying the carrier density the devices show a transition from trap controlled SCLC to trap free/trap filled SCLC. Traps distribution and energies are estimated from the temperature dependent I-V measurements. Poole-Frenkel behaviour, i.e. field dependent mobility is observed in all the polypyrrole samples. The zero field mobility follows Arrhenius behaviour at higher temperatures. Also the temperature variation of mobility displays field dependent and field independent regimes in fully doped and lightly de-doped polypyrrole films. A zero-bias anomaly is observed as the field goes to zero value below 50 K, due to coulomb-blockade transport. Capacitance measurements have shown pseudo inductive behaviour at higher bias, which is also connected with trap-filling regime of PPy devices.
Chapter 4: Current-Voltage anomalies are observed in polythiophene (PTh) and poly (3-methylthiophene) [P3MeT] based devices. The origin of this anomaly is not straight forward in polymer devices, so we investigated it in detail. We propose this is a property specific to the above two materials from various experimental studies. The anomalous behaviour appears when the bias is swept from negative to positive keeping the substrate deposited with polymer as anode. The magnitude of peak to valley current ratio (PVCR) which characterises the merit of device can be varied more than two orders of magnitude by varying the carrier density and as well as by varying scan rate. Since the trap states are also one of the reasons for the origin of this anomaly the rate of filling of these states can be helpful in tuning the magnitude of PVCR. Photo generated carriers in the above devices also help in tuning and controlling the magnitude of anomaly, which can make this device as a suitable candidate for opto-electronic studies. Different conductive substrates such as indium tin oxide, platinum, gold and stainless steel are used for deposition of the above polymers. Top contacts (gold, silver and aluminium) have been also varied to understand the origin of this anomaly. Anomalies are observed with all these different substrates and different top contacts. Finally impedance measurements have shown an elongated tail in the Cole-Cole plot in the region of NDR.
Chapter 5: Impedance measurements on poly (3-hexylthiophene) devices have shown different relaxation mechanism by varying the doping concentration. For moderately doped devices the relaxation mechanism is classical Debye-type, whereas for highly de-doped samples the relaxation time of the carriers is distributed. Charge transport parameters such as contact resistance, mobility and conduction mechanism details can be obtained by identifying and fitting the data to the equivalent circuit model. The relaxation time of the carriers can give rough estimation of mobility and capacitance. The capacitance variation with applied bias gives the nature of conduction mechanism in the devices. If the capacitance variation is unaffected by the applied bias the transport is bulk limited, if it changes significantly the transport can be considered as either contact limited or depletion layer controlled. Current-Voltage measurements also show that Schottky behaviour is present in all the devices. The rectification ratio varies with doping concentration; at one optimum
doping concentration the rectification is very high. I-V measurements on P3MeT devices with varying carrier density have shown a transition in the conduction mechanism from SCLC to contact limited. In the devices with less carrier density the contact limited mechanism is dominating at lower bias voltage and as the bias increases the bulk limited transport takes over. This highlights the role of carrier density in the transport mechanism.
Chapter 6: The conclusions from all the works presented in the thesis are summarised in this chapter. Some of the future directions works are presented.
41
Anjaneyulu, Ponnam. "Charge Transport in Semiconducting Polymer Devices". Thesis, 2012. http://hdl.handle.net/2005/3166.
Testo completoAbstract (sommario):
Understanding the fundamentals of Organic semiconductors is crucial aspect towards the technological applications. Conjugated polymers have shown many interesting physical properties. Especially the electronic and optical properties of these materials have great impact on the daily life. Much work has been devoted to gain the knowledge on the electrical and photo physical properties of these materials. Despite the large number of studies in fabrication and characterisation on these devices some of the fundamental properties like charge transport, carrier generation and its control by doping are not well accomplished.
The Thesis consists of 6 chapters. First chapter is a brief introduction on various properties of semiconducting polymers. Different charge transport models and their basic mechanisms are discussed. Chapter 2 discusses the synthesis, device making and experimental methods used to characterise the polymer devices. Chapter 3 is focused on transport properties in polypyrrole devices and its variation with different experimental conditions. Chapter 4 is aimed to understand the anomalies in the current-voltage characteristics appearing in some of the thiophene based devices. In Chapter 5, the impedance measurement technique is used to characterise the poly (3-hexylthiophene) devices and the outcomes are presented and chapter 6 summarises all the experimental results obtained in this thesis work and presents some future aspects and directions.
Chapter 1: Some of the basic properties and recent advancements in the field of organic semiconductors are discussed in this chapter. Organic semiconductor devices based on conjugated polymers are now becoming alternatives to inorganic semiconductors in many fields. Mobility of these conjugated polymers can be increased by adding dopants and also by choosing appropriate metal contacts for charge injection and extraction. The complexity of the metal-polymer interfaces can be better understood by varying the carrier density and studying their transport properties with various experimental tools.
Chapter 2: The polymer films prepared in this study are electrochemically deposited on to various conducting substrates. The doping and de-doping of the carriers is done by passing a current and reversing its polarity for different time intervals. Device structures for the measurements are obtained by making a top contact on top of the polymer layer. The current-voltage (I-V) and impedance measurements are carried out in metal-polymer-metal geometry. Temperature dependent studies down to 10 K were performed in a continuous flow cryostat to understand the role of temperature in transport studies. Impedance and light measurements are also carried out in the same geometry.
Chapter 3: Transport measurements on polypyrrole devices have shown a space-charge limited (SCLC) conduction, which is also known as bulk property of the materials. I-V curves displayed non-ohmic behaviour at higher voltages and by varying the carrier density the devices show a transition from trap controlled SCLC to trap free/trap filled SCLC. Traps distribution and energies are estimated from the temperature dependent I-V measurements. Poole-Frenkel behaviour, i.e. field dependent mobility is observed in all the polypyrrole samples. The zero field mobility follows Arrhenius behaviour at higher temperatures. Also the temperature variation of mobility displays field dependent and field independent regimes in fully doped and lightly de-doped polypyrrole films. A zero-bias anomaly is observed as the field goes to zero value below 50 K, due to coulomb-blockade transport. Capacitance measurements have shown pseudo inductive behaviour at higher bias, which is also connected with trap-filling regime of PPy devices.
Chapter 4: Current-Voltage anomalies are observed in polythiophene (PTh) and poly (3-methylthiophene) [P3MeT] based devices. The origin of this anomaly is not straight forward in polymer devices, so we investigated it in detail. We propose this is a property specific to the above two materials from various experimental studies. The anomalous behaviour appears when the bias is swept from negative to positive keeping the substrate deposited with polymer as anode. The magnitude of peak to valley current ratio (PVCR) which characterises the merit of device can be varied more than two orders of magnitude by varying the carrier density and as well as by varying scan rate. Since the trap states are also one of the reasons for the origin of this anomaly the rate of filling of these states can be helpful in tuning the magnitude of PVCR. Photo generated carriers in the above devices also help in tuning and controlling the magnitude of anomaly, which can make this device as a suitable candidate for opto-electronic studies. Different conductive substrates such as indium tin oxide, platinum, gold and stainless steel are used for deposition of the above polymers. Top contacts (gold, silver and aluminium) have been also varied to understand the origin of this anomaly. Anomalies are observed with all these different substrates and different top contacts. Finally impedance measurements have shown an elongated tail in the Cole-Cole plot in the region of NDR.
Chapter 5: Impedance measurements on poly (3-hexylthiophene) devices have shown different relaxation mechanism by varying the doping concentration. For moderately doped devices the relaxation mechanism is classical Debye-type, whereas for highly de-doped samples the relaxation time of the carriers is distributed. Charge transport parameters such as contact resistance, mobility and conduction mechanism details can be obtained by identifying and fitting the data to the equivalent circuit model. The relaxation time of the carriers can give rough estimation of mobility and capacitance. The capacitance variation with applied bias gives the nature of conduction mechanism in the devices. If the capacitance variation is unaffected by the applied bias the transport is bulk limited, if it changes significantly the transport can be considered as either contact limited or depletion layer controlled. Current-Voltage measurements also show that Schottky behaviour is present in all the devices. The rectification ratio varies with doping concentration; at one optimum
doping concentration the rectification is very high. I-V measurements on P3MeT devices with varying carrier density have shown a transition in the conduction mechanism from SCLC to contact limited. In the devices with less carrier density the contact limited mechanism is dominating at lower bias voltage and as the bias increases the bulk limited transport takes over. This highlights the role of carrier density in the transport mechanism.
Chapter 6: The conclusions from all the works presented in the thesis are summarised in this chapter. Some of the future directions works are presented.
42
Jayan, Baby Reeja. "Development of efficient, stable organic-inorganic hybrid solar cells". 2012. http://hdl.handle.net/2152/22235.
Testo completoAbstract (sommario):
Developing a fundamental understanding of photocurrent generation processes at organic-inorganic interfaces is critical for improving hybrid solar cell efficiency and stability. This dissertation explores processes at these interfaces by combining data from photovoltaic device performance tests with characterization experiments conducted directly on the device. The dissertation initially focuses on exploring how morphologically and chemically modifying the organic-inorganic interface, between poly(3-hexylthiophene) (P3HT) as the electron donating light absorbing polymer and titanium dioxide (TiO₂) as the electron acceptor, can result in stable and efficient hybrid solar cells. Given the heterogeneity which exists within bulk heterojunction devices, stable interfacial prototypes with well-defined interfaces between bilayers of TiO₂ and P3HT were developed, which demonstrate tunable efficiencies ranging from 0.01 to 1.6 %. Stability of these devices was improved by using Cu-based hole collecting electrodes. Efficiency values were tailored by changing TiO₂ morphology and by introducing sulfide layers like antimony trisulfide (Sb₂S₃) at the P3HT-TiO₂ interface. The simple bilayer device design developed in this dissertation provides an opportunity to study the precise role played by nanostructured TiO₂ surfaces and interfacial modifiers using a host of characterization techniques directly on a working device. Examples introduced in this dissertation include X-ray photoelectron spectroscopy (XPS) depth profiling analysis of metal-P3HT and P3HT-TiO₂ interfaces and Raman analysis of bonding between interface modifiers like Sb₂S₃ and P3HT. The incompatibility of TiO₂ with P3HT was significantly reduced by using P3HT derivatives with -COOH moieties at the extremity of a polymer chain. The role of functional groups like -COOH in interfacial charge separation phenomena was studied by comparing the photovoltaic behavior of these devices with those based on pristine P3HT. Finally, for hybrid solar cells discussed in this dissertation to become commercially viable, high temperature processing steps of the inorganic TiO₂ layer must be avoided. Accordingly, this dissertation demonstrates the novel use of electromagnetic radiation in the form of microwaves to catalyze growth of anatase TiO₂ thin films at temperatures as low as 150 °C, which is significantly lower than that used in conventional techniques. This low temperature process can be adapted to a variety of substrates and can produce patterned films. Accordingly, the ability to fabricate TiO₂ thin films by the microwave process at low temperatures is anticipated to have a significant impact in processing devices based on plastics.text
43
Shih-HsienChien e 錢仕賢. "Comparing the Morphological Alignment of Thiophene- and- Thienothiophene-based Conjugated Polymers :P3HT and PATBT". Thesis, 2019. http://ndltd.ncl.edu.tw/handle/cnp9x8.
Testo completoAbstract (sommario):
碩士國立成功大學
材料科學及工程學系
107
The semiconducting polymer materials draw researcher’s attention due to their device flexibility and solution process ability. Poly(3-hexylthiophene)(P3HT) and its derivatives are the most broadly applicable conjugated polymers such as organic thin-film transistors, organic photovoltaic devices, photodetectors, thermoelectric generators, etc. When considering device performance, charge mobility is an essential element; the higher mobility, the better performance. In organic thin films, random chain alignment impedes charge transport and results in low carrier mobility. Therefore controlling morphology is the key toward high performance organic electronics. This thesis utilizes a strategy called “sandwich casting” to produce unidirectional alignment in polymeric thin films. This method induce the anisotropic capillary force between glass spacers and polymer solution. Through this unique control in microscopic regime , the polymer chain can be uniaxially aligned along the nanogrooved substrate. Comparing different physical modulations such as process temperature and solvents, we developed a reliable methodology to control polymer morphology. Through the AFM images, the macroscopic morphology of polymers shows the fiber-like chain alignment. For microscopic investigation, the polarized Raman spectroscopy is applied. The intensity of Raman on the two polarized directions is quantitatively discussed and is correlated to the degree of anisotropy which indicates the level of uniaxially alignment in molecular level. Key words : Conjugated polymer, Polythiophene, Ordered morphology, anisotropy
44
Su, Mo_Ting, e 蘇睦庭. "Studies of photovoltaic cell from conjugated polymer P3OT doped carbon nanosolids". Thesis, 2005. http://ndltd.ncl.edu.tw/handle/04142513523909476638.
Testo completoAbstract (sommario):
碩士中原大學
應用物理研究所
93
Abstract In this thesis, we study the possibility of improvement of performance for organic photovoltaic cells by various dopants. The photovoltaic cell was primarily fabricated with conjugated polymer poly(3-octyl- thiophene) (P3OT), in conjunction with an additive based on singlewall carbon nanotubes (SWNTs), buckminsterfullerene (C60) or/and the nematic liquid-crystal E7. The samples include five constitutes: ITO/(P3OT+SWNTs)/Al, ITO/(P3OT+C60)/Al, ITO/(P3OT+E7)/Al, ITO/(P3OT+(E7+SWNTs))/Al and ITO/(P3OT+(E7+C60))/Al, and the doping concentration is chosen to be 1 wt%, 3 wt%, 5 wt% or 10 wt%. In view of photocurrent data, it is found that the samples doped with SWNTs perform poorly, likely due to the poor dispersion in the polymeric matrix. As anticipated, doping C60 can promote the photocurrent signal of the samples. The performance in photoconduction for the samples doped with E7 is the best among all samples investigated. From the experimental results of fluorescence spectra, we believe that the mechanism for the dopant E7 in the photoconducting polymer is different from that of carbon nanotubes or C60. We propose that the doapnt E7 may locally help polymeric molecules arrange more orderly and promote charge-carrier transport, leading to the higher photocurrent observed.
45
Peng, Bo-Yan, e 彭博彥. "Effects of mechanical imprinting on the optoelectronic behavior of conjugated polymers in nanofilms: MEH-PPV and P3HT". Thesis, 2015. http://ndltd.ncl.edu.tw/handle/4tbs9d.
Testo completoAbstract (sommario):
碩士國立清華大學
材料科學工程學系
103
The experiment of this study uses the mold with microns (5 um) and sub-micron (0.5 um) pattern-size to imprint on the conjugated polymer, MEH-PPV and P3HT, and the mold of patterns will reproduce onto the film surface of the conjugated polymer. There are several aspects in this study. First, we observe the deformation situation of the imprinted polymer film. And then, we discuss the factors that influence on Photoluminescence (PL) of conjugated polymer after imprinting which caused by the mold size and shape, concentration of the conjugated polymer, initial film thickness, temperature during imprinting, substrate effect, imprinting time and the strength of stress, respectively. Finally, we try to explain the result of the imprinting data by stress relaxation after imprinting and the crystallization of conjugated polymer.
46
Khan, Motiur Rahman. "Nonlinear Charge Transport and Photo-Physical Studies in Conjugated Polymers (P3meT, P3HT) and their Hybrid Composites with Silver Sulfide Quantum Dots". Thesis, 2017. http://etd.iisc.ac.in/handle/2005/4133.
Testo completoAbstract (sommario):
Organic semiconductors have been investigated as an emerging class of materials for their viable applications in electronics. Despite considerable improvement in device properties, a better understanding of the nature of charge transport in these devices and the physics of contacts is crucial to further development of organic devices. The main motivation of this thesis is derived from the fact that physics of disordered systems like conjugated polymer has yet not achieved as concrete understanding as ordered and crystalline systems such as inorganic semiconductors. This thesis investigates the transport properties of electropolymerized thin films by varying the synthesis conditions, carrier density and disorder. Several efforts have been made to understand the non-linear transport phenomena in conjugated polymers. We have also studied the charge transport, charge transfer and photo-physical studies in polymer nanocomposites with inorganic quantum dots. Temperature dependent current-voltage measurements, conductivity and impedance spectroscopy were used to investigate the charge transport mechanism in polymers and nanocomposites. We have investigated the barrier effect on the bulk limited transport in electrochemically doped polymer devies and have shown that deviation in conventional trap limited transport can be modeled by considering the barrier at interface. Effect of doping on disorder and transport show that dopant diffusing from thin films creates disorder traps in the system. We observed that the polymer synthesised at room temperature shows better transport in perpendicular direction than sample prepared at low temperature. This observation was further supported by variable range hopping parameters and Glazman-Matveev model. In the nanocomposite systems, a transition from direct tunneling to thermionic emission and then Poole-Frenkel emission was observed by increasing the quamtum dots weight percentage from 5 to 80.
47
Rezasoltani, Elham. "Excitonic behaviour in polymeric semiconductors : the effect of morphology and composition in heterostructures". Thèse, 2016. http://hdl.handle.net/1866/15942.
Testo completoAbstract (sommario):
La compréhension des interrelations entre la microstructure et les processus électroniques
dans les polymères semi-conducteurs est d’une importance primordiale pour
leur utilisation dans des hétérostructures volumiques. Dans cette thèse de doctorat, deux
systémes diffèrents sont étudiés ; chacun de ces systèmes représente une approche diffèrente
pour optimiser les matériaux en termes de leur microstructure et de leur capacité à
se mettre en ordre au niveau moléculaire.
Dans le premier système, j’ai effectué une analyse complète des principes de fonctionnement
d’une cellule photovoltaïque hybride à base des nanocristaux d’oxyde de
zinc (ZnO) et du poly (3-hexylthiophène) (P3HT) par absorption photoinduite en régime
quasi-stationnaire (PIA) et la spectroscopie PIA en pompage modulé dépendant de la
fréquence. L’interface entre le donneur (le polymère P3HT) et l’accepteur (les nanoparticules
de ZnO), où la génération de charges se produit, joue un rôle important dans
la performance des cellules photovoltaïques hybrides. Pour améliorer le mécanisme de
génération de charges du P3H: ZnO, il est indispensable de modifier l’interface entre
ses constituants. Nous avons démontré que la modification d’interface moléculaire avec
cis-bis (4, 40 - dicarboxy-2, 20bipyridine) ruthénium (II) (N3-dye) et a-Sexithiophen-2
yl-phosphonique (6TP) a améliorée le photocourant et la performance dans les cellules
P3HT: ZnO. Le 6TP et le N3 s’attachent à l’interface du ZnO, en augmentant ainsi l’aire
effective de la surface donneur :accepteur, ce qui contribue à une séparation de charge
accrue. De plus, le 6TP et le N3 réduisent la densité de pièges dans le ZnO, ce qui réduit
le taux de recombinaison des paires de charges.
Dans la deuxième partie, jai introduit une matrice hôte polymérique de polystyréne à
masse molaire ulra-élevée, qui se comporte comme un solide pour piéger et protéger une
solution de poly [2-méthoxy, 5- (2´-éthyl-hexoxy) -1,4-phénylènevinylène- PPV] (MEHPPV)
pour utilisation dans des dispositifs optoèlectroniques quantiques. Des travaux antérieurs
ont montré que MEH-PPV en solution subit une transition de conformation,
d’une conformation enroulé à haute température (phase bleue) à une conformation de
chaîne étendue à basse température (phase rouge). La conformation de la chaîne étendue de la solution MEH-PPV favorise les caractéristiques nécessaires à l’amélioration des
dispositifs optoélectroniques quantiques, mais la solution ne peut pas être incorporées
dans le dispositif. J’ai démontré que la caractéristique de la phase rouge du MEH-PPV
en solution se maintient dans une matrice hôte polymérique de polystyrène transformé de
masse molaire très élevée, qui se comporte comme un solide (gel de MEH-PPV/UHMW
PS), par le biais de la spectroscopie de photoluminescence (PL) dépendant de la température
(de 290K à 80 K). La phase rouge du gel MEH-PPV/UHMW PS se manifeste
par des largeurs de raie étroites et une intensité augmentée de la transition 0-0 de la
progression vibronique dans le spectre de PL ainsi qu’un petit décalage de Stokes entre
la PL et le spectre d’absorption à basse température.
Ces approches démontrent que la manipulation de la microstructure et des propriétés
électroniques des polymères semi-conducteurs ont un impact direct sur la performance
de dispositifs pour leurs développements technologiques continus.Understanding the interrelations between microstructure and electronic processes in polymeric semiconductors is of great importance for their use in bulk heterostructures, as the active part of power-converting devices such as organic photovoltaic cells or light emitting diodes, as well as for quantum optoelectronics applications. In this doctoral thesis, two different systems are investigated; each of these systems represents a different approach to optimize materials in terms of microstructure and their ability to order on the molecular level. In the first system, by means of quasi-steady-state photoinduced absorption (PIA) and pump-modulation-frequency-dependent PIA spectroscopy, I performed a comprehensive analysis of the working principles of a hybrid photovoltaic cell based on nanocrystals of zinc oxide (ZnO) and poly(3-hexylthiophene) (P3HT). The interface surface area between donor (polymer P3HT) and acceptor (ZnO nanocrystals), where charge generation occurs, plays a significant role in the performance of the hybrid photovoltaic cells. To improve the charge generation mechanism of P3HT: ZnO, it is therefore essential to modify the P3HT: ZnO interface area. We demonstrated that molecular interface modification with cis-bis(4,40-dicarboxy-2,20bipyridine) ruthenium (II) (N3-dye) and a-Sexithiophen-2-yl-phosphonic Acid (6TP) as interface modifiers enhanced the photocurrent and performance in P3HT: ZnO cells. 6TP and N3 attach to the ZnO interface, thus increasing the donor:acceptor interface area that contributes to enhanced charge separation. Furthermore, 6TP and N3 reduce the ZnO traps that reduces recombination. In the second part, I introduced a processed solid-like ultra-high-molecular-weight polystyrene polymeric host matrix to trap and protect poly [2-methoxy, 5-(2’-ethylhexoxy)- 1,4-phenylene vinylene-PPV] (MEH-PPV) solution for use in quantum optoelectronic devices. Previous work by others has shown that MEH-PPV in solution undergoes a conformation transition from coiled conformation at high temperatures (blue-phase) to a chain-extended conformation at low temperatures (red-phase). The chain-extended conformation of MEH-PPV solution favours the characteristics needed to improve quantum optoelectronic devices, however the solution cannot be incorporated into the device. We demonstrated that the red-phase feature of MEH-PPV in solution maintains in a processed solid-like ultra-high-molecular-weight polystyrene polymeric host matrix (MEH-PPV/UHMWPS gels), by means of temperature-dependent photoluminescence (PL) spectroscopy (ranged from 290K down to 80 K). The red-phase of MEH-PPV/UHMW PS gels manifest itself as narrow linewidths and enhanced 0-0 line strength in the PL spectrum as well as a small stokes shifts between the PL and absorption spectra at low temperatures. These approaches demonstrate that microstructure manipulation and electronic properties of polymeric semiconductors have a direct impact on the device performance for their continued technological developments.
48
Li, Chien-yi, e 李建毅. "The Gelation Mechanism and Aggregation Structure of Mixed the Conjugated Polymers (P3HT) with Carbon Nanomaterials in Xylene Solutions and It Induce the Photophysical Properties of the Solutions". Thesis, 2013. http://ndltd.ncl.edu.tw/handle/94514962642499601314.
Testo completoAbstract (sommario):
碩士國立臺灣科技大學
材料科學與工程系
101
In this work, we provided insights into effect of the carbon nanomaterials; such as phenyl-C61-butyric acid methyl ester (PCBM) and graphene, aging time and temperature on the gelation mechanism, aggregates structure and its effect on the photophysical properties (UV-vis absorption and Photoluminescence spectra) of Poly(3-hexylthiophene) (P3HT) conjugate polymer in xylene solutions with Dynamic light scattering (DLS), Polarized optical microscopy (POM), UV-visble absorption (UV-vis), and Photoluminescence (PL) spectra, Wide-angle X-ray diffraction (WAXD), scanning electronic microscopy (SEM) and transmission electronic microscopy (TEM) techniques. Firstly, we focus on the gelation mechanism of P3HT and induce its photophysical properties in xylene solution as a function of concentration of P3HT. DLS indicated that the aggregation structure characterized by the normalized intensity-intensity correlation function (A(??-1) and decay time (t) of P3HT in the xylene solution depended strongly on concentration and aging time, where the conjugated chains exhibited a more aggregated as concentration and aging time were raised. Dynamic light scattering and optical microscopy revealed that the gelation was driven by a phase-separation occurred through a spinodal decomposition mechanism, therefore, the gelation mechanism was influence on its photophysical properties of P3HT/xylene solution with aging time. As increase in the aging time, P3HT polymer segments association or crystallization to form aggregates in P3HT/xylene solution. Thus, the intensities of 0-1 and 0-2 singlet energy transformation (640 and 690 nm) in PL spectrum increase remarkable with increasing aging time. The phenomenon may be let us concluded that P3HT/xylene solution occurs the phase-separation mechanism to form a P3HT-enriched domain and an isotropic-enriched domain with aging time as raise. The P3HT-enriched phase was mesomorphic, consisting of some nanowhisker or nanowire morphology and some sheetlike aggregates or membranes of P3HT, which dominated the UV-vis and PL behavior of the gel. On the other hand, the P3HT aggregates and crystallized structures could be disrupted by heating to ca. 45-55 oC as a function of concentration of P3HT, above which the corresponding UV-vis and PL spectra displayed a blue shift because of reduced amount of the aggregates of P3HT for the isotropic P3HT/xylene solution. Then, we provided insights into effect of the weight ratios of PCBM in P3HT/PCBM nanocomposites, temperature, and aging time on the aggregation, and gelation mechanism of P3HT/PCBM/xylene solution and its effect on the photophysical properties of blended P3HT/PCBM in solution at room temperature. UV-vis spectrum, optical microscopy and SEM revealed that the gelation of P3HT/PCBM/xylene solution was driven by phase-separation occurred through P3HT conjugated polymer association and PCBM molecules aggregation in the P3HT/PCBM-enriched domain. Although the phase-separation could proceed to the late stage, the interconnected morphology of P3HT was restrained by the PCBM molecules aggregates to decrease the gel property of the system. The phase-separation behavior of P3HT/PCBM in xylene solution as separate in to four steps: (1) the homogenous P3HT/PCBM/xylene fresh solution occurrence the phase-separation mechanism to form a P3HT/PCBM-enriched domain and a isotropic-enriched domain, (2) in the P3HT/PCBM-enriched domains, P3HT polymer chains associate to form nanowhisker whereas, PCBM molecules aggregate to form sheet-like aggregates with aging time, (3) Upon prolonged isothermal aging time, the nanowhiskers aggregate in to a three-dimensional network structure, and PCBM molecules associate in to nanocrystals with π-π stacked interaction force, and (4) the sheet-like P3HT aggregates were adsorb by PCBM nanocrystals forming flower-like aggregates within P3HT/PCBM-enriched phase. The gelation mechanism dominates the UV-vis and PL behavior with aging time. However, the aggregates of P3HT/PCBM nanocomposite could be disrupted by temperature heating to ca. 40-55 oC as a function of content of PCBM. At higher PCBM content resulting lower phase transition temperature because of reduced the amount of P3HT polymer chains within the aggregates. Finally, we provided insights into effect of the weight ratios of graphene in P3HT/graphene nanocomposites, temperature, and aging time on the aggregation, and gelation mechanism of P3HT/graphene/xylene solution and its effect on the photophysical properties of blended P3HT/graphene in solution at room temperature. The gelation behavior, UV-vis and PL spectra of P3HT/graphene/xylene solution dominate by the graphene content. The phase-separation behavior of P3HT/graphene in xylene solution as separate in to three steps: (1) the homogenous P3HT/graphene/xylene freshly solution occurrence the phase-separation mechanism in to a P3HT/graphene-enriched domain and a isotropic-enriched domain, (2) in the P3HT/graphene-enriched domains, P3HT polymer chains associate to form nanowhisker whereas, PCBM molecules aggregate to form sheet-like aggregates with aging time, (3) Upon prolonged isothermal aging time, the P3HT nanowhiskers were adsorb by graphene aggregates forming cocoon-like aggregates within P3HT/graphene-enriched phase. Within the cocoon-like aggregates, we confirm that the P3HT polymer chains self-assembled for nanowhiskers through π-π stacked interaction and aligned along the nanowhisker axis grow.
49
Varade, Vaibhav. "Charge Transport and Photo-Physical Studies in Conjugated Polymers, Hybrid Nanocomposites and Devices". Thesis, 2014. http://etd.iisc.ac.in/handle/2005/2911.
Testo completoAbstract (sommario):
The main motivation of this thesis is derived from the fact that physics of disordered systems like conjugated polymer has yet not achieved as concrete understanding as ordered and crystalline systems such as inorganic semiconductors. Through the work done in this thesis, several efforts have been made in order to understand basic charge transport (hopping, current injection) phenomena and photo-physical properties (photoluminescence quenching, absorption, photoconductivity) in conjugated polymer and their hybrid composites.
The thesis consists of 7 chapters. Chapter 1 discusses the background knowledge and information of the general properties of conjugated polymers, quantum dots and their hybrid nanocomposites. Chapter 2 deals with the sample preparation and experimental techniques used in this thesis. Chapter 3 elaborates the temperature and field dependent anisotropic charge transport in polypyrrole. Chapter 4 presents an idea to probe and correlate disorder and transport properties using impedance and Raman spectroscopy. Chapter 5 mainly talks about the doping level dependent photophysical and electrical properties of poly(3-hexylthiophene). Chapter 6 reveals the charge transport phenomena in hybrid composites of poly(3,4-ethyldioxythiophene):polysterene sulfonate (PEDOT:PSS) and cadmium telluride quantum dots.
Chapter 1: Conjugated polymers and their hybrid systems are easily processible and cost effective material having huge scope for advanced materials of the future. Although variable range hopping (VRH) is widely accepted to model charge transport in π-conjugated systems, but at very low temperatures, high fields, high carrier concentrations one need to explore other models. Conjugated polymers are anisotropic intrinsically. Therefore, anisotropic charge transport can provide basic insights about the physics of charge hopping. Quantum dots, and their hybrid nanocomposites with semiconducting polymers receiving a huge attention for light emission and photovoltaic purposes. It is important to learn about the charge injection,barrier heights, etc. in order to achieve efficient hybrid devices.
Chapter 2: Synthesis of the samples, both conjugated polymers and quantum dots, and fabrication of hybrid devices is an important and integral part of this thesis. An Electropolymerization technique is used for making polymer samples on conducting substrates. This is quite interesting because one can tune doping level, disorder and thickness simultaneously. Hydrothermal process is adopted to get highly aqua-dispersible quantum dots. Samples are characterized by different techniques like Raman spectroscopy, energy dispersive spectroscopy. Photoluminescence, UV-Vis absorption, transmission electron microscopy and atomic force microscopy are used to explore several properties of the polymer and hybrid nanocomposites.
Chapter 3: It is known that conjugated polymers are intrinsically one–dimensional materials. Therefore it is important to learn anisotropic behavior of these complex systems. Hence, a comparison of electronic transport to their morphology has been carried out and role of carrier density and disorder is discussed further. Both in-plane and out-of-plane charge transport is studied in electrochemically deposited polypyrrole on platinum. Strong anisotropy is observed in the system which is correlated to granular morphology. Field dependence of anisotropic conductivity is also explored. Field scaling analysis shows that all field dependent curves of conductance at different temperatures can fall on to single master curve. Glazman – Matveev model is used to describe nonlinear conduction in field dependence and nonlinearity exponent is estimated. Disorder and carrier density along with the morphological structure like length and orientation of polymer chains with stacking arrangement of different layers in PPy films play an important role in governing the anisotropy in transport properties.
Chapter 4: Two different techniques, namely impedance and Raman spectroscopies are used to probe disorder and transport properties in the polypyrrole. An effort is made to correlate the transport properties to the morphology by probing disorder via two different spectroscopic techniques. Frequency dependence of both real and imaginary part has shown that disorder and inhomogeneity varies in different PPy devices, which thus affect the transport properties like conductivity and mobility. Mobility values along the thickness direction for each sample reveal the impact of disorder on out-of¬plane geometry. A circuit based on consideration of the distributed relaxation times, is
successfully used to obtain the best fit for the Cole–Cole plot of various PPy devices. FWHM of the de-convoluted peaks of Raman spectra is attributed to the change in distribution of the conjugation length in the PPy films.
Chapter 5: The main focus of this chapter is the qualitative exploration of different photo-physical and electrical properties of electropolymerized poly(3-hexylthiophene) and their dependence on doping level. Photoluminescence quenching, band edge shifting in absorption spectra, electrochromic effect, significant enhancement in photocurrent at optimum doping level, two relaxation behaviors in reactance spectra and presence of negative capacitance at low frequencies are distinct features which are observed in poly(3-hexylthiophene) in this work. Quenching in photoluminescence intensity is attributed to charge transfer occurring between polymer chains and dopant ions. Two semicircles in the Cole-Cole plots refer to two type of relaxation process occurring in bulk layer and at interface. Frequency response of capacitance at higher bias and lo side of frequency shows a negative capacitance due to the relaxation mechanism associated with the space-charge effect.
Chapter 6: Synthesis of quantum dots and fabrication of hybrid devices is one of the catchy parts of this chapter. Huge quenching photoluminescence intensity and very high increment (~ 400 %) in photocurrent clearly depict the charge transfer at molecular level. Temperature dependent current–voltage characteristics show the absence of thermionic emission since the barrier height is more than the thermal energy of the carriers. Further analysis confirms that the charge carrier injection of ITO/PPCdTe3/Al device is controlled by tunneling processes. The hybrid system has shown a peculiar transition from direct tunneling to Fowler–Nordheim tunneling mechanism which is because of the change in shape of the barrier height from trapezoidal to triangular type with increase in applied electric field.
Chapter 7: The conclusions of the different works presented in this thesis are coherently summarized in this thesis. Thoughts and prospective for future directions are also summed up.
50
Varade, Vaibhav. "Charge Transport and Photo-Physical Studies in Conjugated Polymers, Hybrid Nanocomposites and Devices". Thesis, 2014. http://etd.iisc.ernet.in/handle/2005/2911.
Testo completoAbstract (sommario):
The main motivation of this thesis is derived from the fact that physics of disordered systems like conjugated polymer has yet not achieved as concrete understanding as ordered and crystalline systems such as inorganic semiconductors. Through the work done in this thesis, several efforts have been made in order to understand basic charge transport (hopping, current injection) phenomena and photo-physical properties (photoluminescence quenching, absorption, photoconductivity) in conjugated polymer and their hybrid composites.
The thesis consists of 7 chapters. Chapter 1 discusses the background knowledge and information of the general properties of conjugated polymers, quantum dots and their hybrid nanocomposites. Chapter 2 deals with the sample preparation and experimental techniques used in this thesis. Chapter 3 elaborates the temperature and field dependent anisotropic charge transport in polypyrrole. Chapter 4 presents an idea to probe and correlate disorder and transport properties using impedance and Raman spectroscopy. Chapter 5 mainly talks about the doping level dependent photophysical and electrical properties of poly(3-hexylthiophene). Chapter 6 reveals the charge transport phenomena in hybrid composites of poly(3,4-ethyldioxythiophene):polysterene sulfonate (PEDOT:PSS) and cadmium telluride quantum dots.
Chapter 1: Conjugated polymers and their hybrid systems are easily processible and cost effective material having huge scope for advanced materials of the future. Although variable range hopping (VRH) is widely accepted to model charge transport in π-conjugated systems, but at very low temperatures, high fields, high carrier concentrations one need to explore other models. Conjugated polymers are anisotropic intrinsically. Therefore, anisotropic charge transport can provide basic insights about the physics of charge hopping. Quantum dots, and their hybrid nanocomposites with semiconducting polymers receiving a huge attention for light emission and photovoltaic purposes. It is important to learn about the charge injection,barrier heights, etc. in order to achieve efficient hybrid devices.
Chapter 2: Synthesis of the samples, both conjugated polymers and quantum dots, and fabrication of hybrid devices is an important and integral part of this thesis. An Electropolymerization technique is used for making polymer samples on conducting substrates. This is quite interesting because one can tune doping level, disorder and thickness simultaneously. Hydrothermal process is adopted to get highly aqua-dispersible quantum dots. Samples are characterized by different techniques like Raman spectroscopy, energy dispersive spectroscopy. Photoluminescence, UV-Vis absorption, transmission electron microscopy and atomic force microscopy are used to explore several properties of the polymer and hybrid nanocomposites.
Chapter 3: It is known that conjugated polymers are intrinsically one–dimensional materials. Therefore it is important to learn anisotropic behavior of these complex systems. Hence, a comparison of electronic transport to their morphology has been carried out and role of carrier density and disorder is discussed further. Both in-plane and out-of-plane charge transport is studied in electrochemically deposited polypyrrole on platinum. Strong anisotropy is observed in the system which is correlated to granular morphology. Field dependence of anisotropic conductivity is also explored. Field scaling analysis shows that all field dependent curves of conductance at different temperatures can fall on to single master curve. Glazman – Matveev model is used to describe nonlinear conduction in field dependence and nonlinearity exponent is estimated. Disorder and carrier density along with the morphological structure like length and orientation of polymer chains with stacking arrangement of different layers in PPy films play an important role in governing the anisotropy in transport properties.
Chapter 4: Two different techniques, namely impedance and Raman spectroscopies are used to probe disorder and transport properties in the polypyrrole. An effort is made to correlate the transport properties to the morphology by probing disorder via two different spectroscopic techniques. Frequency dependence of both real and imaginary part has shown that disorder and inhomogeneity varies in different PPy devices, which thus affect the transport properties like conductivity and mobility. Mobility values along the thickness direction for each sample reveal the impact of disorder on out-of¬plane geometry. A circuit based on consideration of the distributed relaxation times, is
successfully used to obtain the best fit for the Cole–Cole plot of various PPy devices. FWHM of the de-convoluted peaks of Raman spectra is attributed to the change in distribution of the conjugation length in the PPy films.
Chapter 5: The main focus of this chapter is the qualitative exploration of different photo-physical and electrical properties of electropolymerized poly(3-hexylthiophene) and their dependence on doping level. Photoluminescence quenching, band edge shifting in absorption spectra, electrochromic effect, significant enhancement in photocurrent at optimum doping level, two relaxation behaviors in reactance spectra and presence of negative capacitance at low frequencies are distinct features which are observed in poly(3-hexylthiophene) in this work. Quenching in photoluminescence intensity is attributed to charge transfer occurring between polymer chains and dopant ions. Two semicircles in the Cole-Cole plots refer to two type of relaxation process occurring in bulk layer and at interface. Frequency response of capacitance at higher bias and lo side of frequency shows a negative capacitance due to the relaxation mechanism associated with the space-charge effect.
Chapter 6: Synthesis of quantum dots and fabrication of hybrid devices is one of the catchy parts of this chapter. Huge quenching photoluminescence intensity and very high increment (~ 400 %) in photocurrent clearly depict the charge transfer at molecular level. Temperature dependent current–voltage characteristics show the absence of thermionic emission since the barrier height is more than the thermal energy of the carriers. Further analysis confirms that the charge carrier injection of ITO/PPCdTe3/Al device is controlled by tunneling processes. The hybrid system has shown a peculiar transition from direct tunneling to Fowler–Nordheim tunneling mechanism which is because of the change in shape of the barrier height from trapezoidal to triangular type with increase in applied electric field.
Chapter 7: The conclusions of the different works presented in this thesis are coherently summarized in this thesis. Thoughts and prospective for future directions are also summed up.