Ongoing efforts to improve the efficiency of organic photovoltaic cells emphasize the significance of the architecture of molecular assemblies in thin films, at nanometer and micron length scales, to enhance both exciton diffusion and charge transport, in donor and acceptor layers. Controlled growth of molecules via self-assembly techniques presents new opportunities to develop nano-structured organic thin films for electronic devices. This thesis is focused on controlling the orientation of phthalocyanine molecular assemblies in thin films in order to demonstrate the impact of microscopic control of molecular order on electrical properties and organic solar cell device performance.The studies performed here provide insights into the self-assembling behavior, film morphology, nanoscale electrical conductivity, and photovoltaic properties of a disk-shaped peripherally substituted phthalocyanine (Pc) molecule possessing amide functional groups in the side chains. Amide functionality was integrated in the side chains of this phthalocyanine molecule with the purpose of increasing the intra-columnar interaction through formation of a hydrogen bonding network between molecules, and to guide columnar orientation in a preferred direction via specific surface-molecule interactions. It is realized that molecule-substrate interactions must dominate over molecule-molecule interactions to achieve control over the deposition of molecules in a preferred direction for organic solar cell applications. Microscopic imaging and spectroscopic studies confirm the formation of flat-lying, well ordered, layered phthalocyanine films as anticipated.The remarkable electrical conductivity of the flat-lying phthalocyanine molecules, as studied by Conducting tip Atomic Force Microscopy (C-AFM) provide the impetus for the formation of organic solar cells based on layers of these hydrogen bonding phthalocyanine molecules. The photocurrent from devices that are made with the ordered Pc molecules and disordered Pc molecules as the primary photoactive donor layer, and vacuum deposited C60 as the acceptor material, were evaluated. The results presented here demonstrate the feasibility of increasing the photogenerated current by controlling the molecular organization in the photo active layer.

L’utilisation des nanotubes de carbone (CNT) dans les cellules photovoltaïques (PV) se limitent à leur application comme électrodes ou comme dopant dans la couche active à cause de leur conductivité extrêmement élevée provocant des courts-circuits au sein de la cellule. Dans le cadre de cette thèse, nous avons proposé et validé un nouveau concept consistant à développer les SWNT comme matériaux actifs accepteurs alternatifs au PCBM (dérivé de fullerène) pour le photovoltaïque organique.Nous avons développé une voie de synthèse chimique basée sur la fonctionnalisation contrôlée des SWNT et la quantification de leur degré de fonctionnalisation. Ce nouveau concept permettra l’élaboration des SWNT « sur mesure » avec des conductivités et des propriétés optiques et électrochimiques modulables et adéquats avec les propriétés requise pour une intégration dans les dispositifs photovoltaïques en hétérojonctions avec les polymères pi-conjugués donneurs commerciaux.Il a été mis en évidence grâce aux caractérisations des propriétés finales des SWNT synthétisés que la conductivité, l’absorption dans l’UV-visible et les propriétés électrochimiques évoluent graduellement selon deux modes en fonction du degré de fonctionnalisation. De plus, la fonctionnalisation contrôlée des SWNT induit un effet dispersant permettant de faciliter leur intégration dans les dispositifs PV en utilisant les technologies de mise en œuvre par voie solvant existantes comme l’impression par jet d’encre ou roll-to-roll l’élaboration des couches minces par voie solvant. La preuve de ce concept a été validée grâce aux tests en cellules PV avec un polymère standard commercial P3HT et un polymère à faible gap optique synthétisé. / Controlled modulation of intrinsic functional (absorption, band gap, conductivity) and physico-chemical properties (dispersability, solvent-processability) of CNTs could broaden up their application potential in nanotechnology. However, it has been an ambitious synthetic goal for more than a decade. In this work, we developed an efficient methodology to do so in a mastered manner on single-walled carbon nanotubes (SWNT). It involves the meticulous functionalization based on gradual formation of covalent aryl bonds. It was proven that, the intrinsic electrical conductivity, optical and electrochemical properties of the functionalized SWNTs could be gradually modulated in two steps depending on the functionalization degree. The so- controlled covalent functionalization was the basic synthetic technique to make SWNT easier to manipulate and tolerably soluble, with modulated electrical and electrochemical properties, so that the performances in photovoltaic cells were unusually appreciated. Unsorted functionalized SWNTs were employed in organic photovoltaic (OPV) cells as electron acceptors or dopants with commercial polymer (P3HT) and novel, synthesized low bandgap copolymer, respectively.

Philosophiae Doctor - PhD / Fossil fuels are part of fuels that are formed from natural processes and they are called non-renewable sources of energy. These include natural gas, coal and oil. They have been used for decades to produce energy globally. However, there are some factors that related with the use of fossil fuels which results in an increase in the requirement of large amounts of energy. In addition, the use of fossil fuels as energy source has a negative impact on the environment and they cannot be reused. It is expected that at some point they will run out. Thus, a need for a renewable, clean and plentiful source of energy is urgent. Solar energy is one of the energy sources that may overcome fossil fuel drawbacks.

Orientador: Ana Flávia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-26T15:49:22Z (GMT). No. of bitstreams: 1 SakerNeto_Nicolau_M.pdf: 15094468 bytes, checksum: d3c20b6e7dbd840a984fe7d8b1b365a8 (MD5) Previous issue date: 2014 / Resumo: Entre as alternativas promissoras para a produção de energia elétrica de modo econômico e ambientalmente sustentável está o aproveitamento da energia luminosa do Sol pelo efeito fotovoltaico. Células fotovoltaicas orgânicas fazem parte da mais nova geração de células solares, e prometem ser produzidas em larga escala a custo reduzido. Entretanto, células orgânicas atualmente estão limitadas por eficiências comparativamente baixas. O objetivo deste trabalho é introduzir derivados de grafeno em células solares orgânicas poliméricas como aceitador de elétrons e transportadores de cargas na camada absorvedora de luz, em substituição parcial ou total aos atuais materiais mais empregados, derivados de fulerenos C60 e C70. Óxido de grafeno (GO) foi obtido a partir da oxidação de grafite mineral utilizando-se o método de Hummers com modificações. Amostras de grafenos quimicamente modificados (CMGs) foram sintetizadas pela reação direta de dispersões de óxido de grafeno com ácido 2-tiofenoacético (TAA) por uma esterificação de Steglich, ou após um tratamento de óxido de grafeno em meio básico com hidróxido de tetrabutilamônio (TBAH). Os CMGs apresentaram funcionalização bastante limitada, tendo ocorrido principalmente uma desoxigenação dos derivados de grafeno. Ainda assim, os CMGs puderam ser dispersos no solvente usado para a preparação da camada absorvedora de luz, 1,2-diclorobenzeno. Os materiais sintetizados foram aplicados em células poliméricas baseadas no polímero poli(3-hexiltiofeno) (P3HT) e no derivado de fulereno [6,6]-fenil-C71-butanoato de metila (PC71BM), e os parâmetros fotovoltaicos resultantes foram obtidos. As eficiências de conversão fotovoltaicas em células contendo CMGs foram potencialmente limitadas pelo processo de desoxigenação / Abstract: Among the promising alternatives for the economically and environmentally sustainable production of electrical energy is the harnessing of the Sun's luminous energy by the photovoltaic effect. Organic photovoltaic cells are part of the newest generation of solar cells, promising large-scale production at reduced costs. However, organic cells are currently limited by comparatively low efficiencies. The objective of this work is to introduce graphene derivatives in polymer organic solar cells as electron acceptors and charge transporters in the light-absorbing layer, partially or fully replacing the currently most used materials, derivatives of C60 and C70 fullerenes. Graphene oxide (GO) was obtained by the oxidation of mineral graphite using a modified Hummers' method. Samples of chemically modified graphenes (CMGs) were synthesized by the direct reaction of graphene oxide dispersions with 2-thiopheneacetic acid (TAA) via Steglich esterification, or after treatment of graphene oxide in basic medium with tetrabutylammonium hydroxide (TBAH). The CMGs showed very limited functionalization and the main occurrence was a deoxygenation of the graphene derivatives. Still, the CMGs were dispersible in the solvent used for the preparation of the light-absorbing layer, 1,2-dichlorobenzene. The synthesized materials were applied in polymer cells based on the polymer poly(3-hexylthiophene) (P3HT) and the fullerene derivative [6,6]-phenyl-C71-butyl methyl ester (PC71BM) and the resulting photovoltaic parameters were obtained. The photovoltaic conversion efficiencies for cells containing CMGs were potentially limited by the deoxygenation process / Mestrado / Quimica Organica / Mestre em Química

Der Schwerpunkt der vorgelegten Arbeit lag in der Bestimmung der Energieniveaus an allen Grenzflächen in bestimmten heterostrukturierten Polymer/Polymer- und Polymer/Molekül basierten Solarzellen. Die elektronische Charakterisierung erfolgte mittels Photoelektronenspektroskopie. Morphologie und Schichtdicke der aufgeschleuderten Filme wurden mit den komplementären Analysetechniken UV-vis Absorptionsspektroskopie, Rasterkraftmikroskopie sowie Röntgenphotoelektronenspektroskopie bestimmt. An der PEDT:PSS-Anode/Polymer-Grenzschicht wurden Änderungen im Vakuumniveau von bis zu 0,65 eV gemessen. Die Polymerabscheidung führte zu einer Erniedrigung der Substrataustrittsarbeit, auch wenn die Polymerionisationsenergie mehrere 100 meV größer als die ursprüngliche PEDT:PSS-Austrittsarbeit war. Eine detailierte Analyse der PEDT:PSS/Polymer Grenzflächen ausgehend von Submonolagen zu Multilagen zeigte verschiedene Ursachen für die Änderungen des Vakuumniveaus als verantwortlich. Zweitens: an Donator/Akzeptor-Grenzflächen wurden Änderungen im Vakuumniveau von bis zu 0,35 eV festgestellt, welche die solare Bandlücke (PVG) und folglich die Höchstgrenze der Leerlaufspannung (VOC) beeinflusst. Ein Vergleich aller Resultate der Grenzflächenanalyse mit den Solarzellen Parametern bestätigte PVG als obere Schranke von VOC. Der Energieunterschied zwischen PVG und VOC, der ein Maß für die Verluste in der Solarzelle darstellt, war für reine Polymerheteroübergänge größer als für Polymer/Molekül-Heterostrukturen mit einem Minimum bei 0,5 eV. Drittens: parallel zum Aufbau der Akzeptor/Kathoden-Grenzfläche veränderte sich das Vakuumniveau um ca. 1 eV, bedingt durch das Pinning des Kathoden-Ferminiveaus (EF) an unbesetzte Grenzflächenzuständen. Die energetische Lage dieser Zustände bezüglich EF entschied dabei über die Stärke der Diffusionsspannung in der Solarzelle, welche bei Beleuchtung der entstandenen Solarzellenstruktur durch eine lichtinduzierte Photospannung ausgeglichen wurde. / The main focus of this work was to provide a comprehensive picture of the energy level alignment at the multitude of interfaces that occur in selected polymer/polymer and polymer/small molecule heterojunction photovoltaic cells. The electronic characterization was performed using photoelectron spectroscopy. Morphology and thickness of spin coated thin films was investigated using a complementary technique approach employing UV-vis absorption spectroscopy, atomic force microscopy, and X ray photoelectron spectroscopy. At the PEDT:PSS anode/polymer interface vacuum level shifts up to 0.65 eV were observed. Polymer deposition decreased the substrate work function (WF even though the polymer ionization energy was several 100 meV higher as the initial PEDT:PSS WF. An in depth analysis of the PEDT:PSS/polymer interface from sub-monolayer to multilayer coverage revealed highly diverse origins for the observed vacuum level shifts. Secondly, investigations of the donor/acceptor interfaces revealed vacuum level shifts up to 0.35 eV that influence the photovoltaic gap (PVG) at the heterojunction and, therefore, the upper limit of the open circuit voltage (VOC) in the device. Correlating device data and all results of the interface analysis, PVG was finally confirmed as an upper limit for VOC. The energy difference (eV) between PVG and experimentally determined VOC, which was assigned to losses in the device, was found to be higher for all polymer heterojunctions compared to polymer/small molecule cells with a minimum at eV = 0.5 eV. Third, cathode/acceptor interface formation was accompanied by interfacial vacuum level shifts of ca. 1 eV caused by Fermi level (EF) pinning at interfacial gap states. The exact position of the acceptor pinning level with respect to EF of the anode determines the strength of the built in field in the device that was found to be fully counterbalanced by a photovoltage induced by in situ illumination of the resulting OPVC-like sample structures.

Das Ziel der Arbeit ist die Herstellung und die Charakterisierung von Heterostrukturen des organischen Halbleiters Pentazen (PEN) mit diversen konjugierten organischen Materialien im Hinblick auf das Anwendungspotenzial im Bereich der organischen Elektronik. Für die Untersuchung von PEN-Heterostrukturen mit (i) Fulleren (C60), (ii) Perfluoropentazen (PFP) und (iii) 6,13-Pentazenchinon (PQ) wurden mehrere komplementäre experimentelle Techniken angewendet: Röntgenbeugung, Schwingungsspektroskopie, Rasterkraftmikroskopie und Photoelektronenspektroskopie. (i) Für PEN - Heterostrukturen mit C60 wurden die elektronischen, strukturellen und morphologischen Eigenschaften mit der Leistung von organischen Solarzellen (OSZ) für geschichtete und gemischte Systeme korreliert. Dabei wurde gezeigt, dass morphologische anstatt struktureller oder energetischer Ursachen die Leistungsunterschiede der beiden untersuchten Zelltypen erklären. (ii) Strukturuntersuchungen wurden an reinen PFP-Filmen, sowie an geschichteten und gemischten Heterostrukturen mit PEN durchgeführt. Es wurde die Struktur der PFP-Dünnfilmphase gelöst und das Wachstum von PEN+PFP Mischkristallen gezeigt, welche erfolgreich angewandt wurden, um die Ionisationsenergie (IE) des Films mit dem Mischungsverhältnis durchzustimmen. Dies wurde durch die Existenz von innermolekularen polaren Bindungen (C-H und C-F für PEN und PFP) erklärt. (iii) Für reine PQ-Filme wurde die Struktur der PQ-Dünnfilmphase gelöst (ein Molekül pro Einheitszelle). Es wurde eine stark orientierungsabhängige IE von PQ und PEN gefunden und gezeigt, dass die Energieniveaulagen für die Anwendung in OSZ geeignet sind. Die Untersuchung von Mischsystemen zeigte phasensepariertes Wachstum ohne Hinweise auf Interkalation, selbst bei PQ Konzentrationen von nur 2%. Weiters wurde gezeigt, dass O2 und Wasser keine nachhaltigen Auswirkungen auf PEN-Filme zeigen, wohingegen Singlett-Sauerstoff und Ozon diese angreifen und flüchtige Reaktionsprodukte liefern. / The scope of this work is the combination of the organic semiconductor pentacene (PEN) with different conjugated organic molecules to form application relevant heterostructures in vacuum sublimed films. Using x-ray diffraction (XRD), vibrational spectroscopy, atomic force microscopy and photoelectron spectroscopy, PEN heterostructures with (i) fullerene (C60), (ii) perfluoropentacene (PFP) and (iii) 6,13-pentacenequinone (PQ) were thoroughly characterized to judge on the respective application potential in organic electronics. (i) PEN heterostructures with C60 were investigated regarding the correlation of energetic, structural and morphological properties with the performance of organic photovoltaic cells (OPVCs) for both layered and mixed structures. Morphological rather than energetic or structural issues account for performance differences of bulk-heterojunction OPVCs compared to layered devices. (ii) XRD investigations were carried out on pure PFP films, on layered and mixed heterostructures with PEN. The thin-film polymorph of PFP was solved and it is shown that blended films form a mixed crystal structure, which led to the finding that the ionization energy (IE) of organic films composed of molecules with intramolecular polar bonds (like C-H and C-F for PEN and PFP, respectively) can be tuned through the mixing ratio. (iii) A so far unknown thin-film polymorph of PQ on SiO2 substrates was solved using XRD reciprocal space mapping evidencing a loss of the herringbone arrangement known from the PQ bulk structure. For PEN heterostructures with PQ a highly molecular-orientation dependent IE and energy level offsets interesting for the use in OPVCs were found. Mixed films of PEN and PQ exhibit phase separation and no intercalation was found even at PQ concentrations as low as 2%. Finally, it is shown that O2 and water do not react noticeably with PEN, whereas singlet oxygen and ozone readily oxidize PEN films producing volatile reaction products instead of PQ.

Une cellule photovoltaïque organique (OPV) consiste en un empilement de couches minces et comporte une électrode transparente, constituée le plus souvent par une couche mince d’oxyde d’indium dopé à l’étain (ITO). Des matériaux alternatifs sans indium, déposables par voie liquide à l’air ambiant, et sur de grandes surfaces souples plus adaptées à la filière OPV, sont actuellement l’objet d’un grand nombre de recherches. Les nanofils d’argent (Ag NWs) représentent un sérieux candidat pour remplacer l’ITO et sont l’objet de ce travail de thèse. Une méthode de dépôt des Ag NWs par spray à air sur des substrats de PET a été développée en vue de réaliser des films conducteurs et transparents sur une grande surface souple. Puis ces électrodes transparentes ont été intégrées dans des cellules OPV sur substrat souple avec des rendements comparables à l’ITO. Les dépôts par voie liquide ont été privilégiés (spray-coating, Dr Blade), excepté pour l’électrode supérieure en argent, évaporée sous vide. Enfin les cellules ont été interconnectées en série pour former un module OPV, plus efficace en termes de puissance électrique délivrée. Une étude sur l’ablation sélective de couches de l’empilement OPV par laser est également présentée pour la fabrication de modules. / An organic photovoltaic (OPV) cell consists of a thin-layer stack which includes a transparent electrode, usually made of indium tin-doped oxide (ITO). Alternative, indium-free materials, deposited in air with a wet deposition process on large, flexible substrates that are more compatible with the OPV field are currently widely investigated. Silver nanowires (Ag NWs), which represent a serious candidate to replace ITO, are the subject of this thesis. In this work a method to deposit Ag NWs on PET substrates by air spray-coating has been developed : efficient patterned conductive and transparent coatings could be processed on a large, flexible substrate. This transparent electrode was then integrated in flexible and large area OPV cells, with efficiencies comparable to ITO. Wet deposition techniques were preferred except for the silver top electrode, evaporated under vacuum. OPV cells were eventually interconnected in series in order to make an OPV module, delivering a higher electrical output. A study on selective laser ablation of layers in the OPV stack is also shown towards module processing.

The dissertation is focused on the study of electric and especially dielectric properties of thin film organic materials with their huge potential for optoelectronics and other industrial sectors. The theoretical part deals with the use of organic materials in organic photovoltaic cells, the methods of deposition techniques and characterization. The theoretical knowledge of the dielectric spectroscopy, including methods for determining the physical properties and evaluation of experimental data are also described. The experimental part is devoted to the study of small molecule organic solar cells with bulk heterojunction composed of electron donor molecule of DPP(TBFu)2 and electron acceptor fullerene derivatives, such as PC60BM, PC70BM and TC60BM. The experimental part is divided into two main parts. The first part deals with the study of processes occurring at the interface between the active layer and the contact; the second part is focused on transport processes inside the structure of photovoltaic cells and also contains a study of perovskite solar cells.

Ce travail de recherche pluridisciplinaire a consisté en l'étude de cellules photovoltaïques organiques à base de nouveaux copolymères à blocs de type rigide-flexible. L'idée était de proposer une alternative aux mélanges donneur/accepteur, dont la morphologie en film est très difficile à contrôler, en élaborant de nouveaux matériaux conjugués capables de s'auto-organiser et de créer une nano-structuration de la couche active, permettant ainsi d'optimiser certains paramètres du processus photovoltaïque (dissociation de l'exciton, conduction des charges vers les électrodes). La première étape a consisté à développer une synthèse simplifiée et versatile de copolymères constitués d'un bloc conjugué donneur (poly(3-hexylthiophène), d'un bloc flexible polystyrène, et d'un accepteur d'électron (C60). La seconde étape a consisté à caractériser ces matériaux originaux en tant que couche active ou compatibilisants dans des dispositifs photovoltaïques organiques et ainsi montrer leur potentiel. / This multidisciplinary work deals with the study of organic photovoltaic cells based on new rod-coil block copolymers. The aim was to replace donor/acceptor blends which are currently limited by poor control over their thin-film morphology. It was expected that the new materials may self-assemble to give a nano-structuration of the active layer, and thereby optimize the principal physical photovoltaic processes, namely exciton separation and conduction of charge-carriers through the film to the electrodes. A versatile and simplified synthesis of rod-coil copolymers consisting of a donor conjugated block [poly(3-hexylthiophene], a flexible block (polystyrene) and an electron acceptor (C60) was developed. The characterization of the new materials demonstrated their potential as an active layer or compatibilizer in photovoltaic devices.

Die vorliegende Arbeit beschäftigt sich mit der Leistungssteigerung organischer Solarzellen durch Änderung der Geometrie an der Donor-Akzeptor Grenzfläche und dem Einstellen der elektronischen Eigenschaften von Grenzflächen durch molekulares p-Dotieren. Kristalline und gleichmäßige Nanosäulen aus dem organischen Halbleiter Pentazen wurden durch glancing angle deposition (GLAD) hergestellt, die einen ineinandergreifenden Heteroübergang zu Methanofulleren [6,6]-Phenyl-C61-Butansäure Methylester (PCBM) als Akzeptor ermöglichten. Die Kurzschlussspannung der nanosäulenbasierten Solarzellen war signifikant erhöht im Vergleich zu planaren Heteroübergängen zwischen denselben Materialien. Die Leistungssteigerung der Solarzellen konnte maßgebend der vergrößerten Grenzfläche zugewiesen werden, wegen des verringerten Einflusses der kurzen Exciton Diffusionslänge. Molekulares p-Dotieren mit Tetrafluorotetracyanoquinodimethan (F4TCNQ) als Dotand in polyfuranbasierten Solarzellen wurde für verschiede Dotierkonzentrationen untersucht. Ultraviolettphotoelektronenspektroskopie wurde verwendet, um die Veränderungen der Energieniveaus mit zunehmender Dotierkonzentration zu analysieren, welche zu einer Vergrößerung der 0,2 V Kurzschlussspannung auf bis zu 0,4 V führte. Nach Kombination dieser Beobachtung mit Ergebnissen an dotierten Polymerfilmen, insbesondere bezüglich deren Morphologie und Absorptionsverhalten, wurde vorgeschlagen, dass ein resultierender Dipol an der Donor-Akzeptorgrenzfläche präsent ist. Zusammenfassend zeigt die vorliegende Arbeit das Potential sowohl der GLAD Technik als auch des molekularen, elektrischen Dotierens für die Leistungsverbesserung organischer Solarzellen. / The present work mainly focuses on improving the performance of OPVCs by tailoring the donor-acceptor interface geometry and by tuning the electrical properties of interfaces with p-type molecular doping. Crystalline and uniform nanocolumns of pentacene (PEN) and diindenoperylene (DIP) were fabricated by glancing angle deposition (GLAD), forming an interdigitated donor/acceptor heterojunction with [6,6]-phenyl-C61-butyric acid methyl ester (PCBM) and/or fullerene as the electron acceptor. The short circuit current of nanocolumn-based OPVCs increased significantly compared to planar heterojunction OPVCs made from the same materials. The performance improvement of OPVCs had been verified to be contributed decisively by the donor-acceptor interface area enlargement because of reduced impact of short exciton diffusion length in organic materials. P-type molecular doping as applied in polyfuran (PF) based OPVCs was investigated by using tetrafluorotetracyanoquinodimethane (F4-TCNQ) as the dopant for various doping ratios. Ultraviolet photoelectron spectroscopy (UPS) was applied to analyze the energy level shift with increasing doping ratio leading to the enlargement of the open circuit voltage in OPVCs, from 0.2 V to close to 0.4 V. Combining this observation with the results of doped polymer films, their morphology and absorption behavior, a net dipole pointing towards the donor material at the donor-acceptor interface of OPVCs is proposed. Overall, this work demonstrates the potential of both the GLAD technique and molecular electrical doping for improving the performance of OPVCs.