Submitted by Rosivalda Pereira (mrs.pereira@ufma.br) on 2017-06-07T18:43:28Z No. of bitstreams: 1 LuzyannePereira.pdf: 2863158 bytes, checksum: ff3a4e65449af34c7e12b19e0f749f60 (MD5) / Made available in DSpace on 2017-06-07T18:43:28Z (GMT). No. of bitstreams: 1 LuzyannePereira.pdf: 2863158 bytes, checksum: ff3a4e65449af34c7e12b19e0f749f60 (MD5) Previous issue date: 2011-08-30 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / In this dissertation we present, by computational simulations based in the density functional theory implemented in the SIESTA code, a study on the electronic and energetic properties of face centered cubic (fcc) and body centered cubic (bcc) crystal strutures interspersed with FeCl3 and CrO3 molecules composed by fullerene C60. For this study we used LDA and GGA approximations to represent the exchange-correlation term. Our results suggest that fcc-C60 and bcc-C60 structures interspersed with FeCl3 and CrO3 molecules are stable in terms of the LDA approximation, with the structure interspersed with CrO3 being more energetically favorable . The electronic properties of these systems were analysed by means of projected density of states (PDOS). We have observed that the electronic properties of fcc-C60/bcc-C60 were a ect when interspersed with FeCl3 and CrO3 molecules. The pure fcc-C60/bcc-C60 structures are semiconductor materials with band gap energy around 1,58 eV. When the fcc-C60 interacts with FeCl3 and CrO3 molecules the band gap energy changes to 0.68 eV (semiconductor character ) and almost zero (metalic character), respectively. In the other hand, the bcc-C60 structure interacting with FeCl3 and CrO3 molecules presents metalic and semiconductor (with decreasing of the band gap from 1.58 to 1.20 eV) character, respectively. / No presente trabalho estudamos as propriedades energeticas e eletronicas do solido C60, nas estruturas cubica de face centrada e cubica de corpo centrado, intercalado com as moleculas FeCl3 e CrO3, atraves de simulacão computacional de primeiros princípios baseada na teoria do funcional da densidade, implementada no programa computacional SIESTA. Este estudo foi realizado considerando as aproximações LDA e GGA para o termo de troca e correlação. Analisando o resultado da interação do C60 nas estruturas fcc e bcc com as moleculas FeCl3 e CrO3, observamos que os sistemas sao mais estaveis na aproximacao LDA, sendo que o sistema CrO3/fcc (bcc) é energeticamente mais favoravel. As propriedades eletronicas destes sistemas sao analisadas atraves da densidade de estados projetada (PDOS). As propriedades eletronicas do solido C60 nas estruturas fcc e bcc puro sao afetadas pela intercalaçao das moleculas FeCl3 e CrO3. O C60 na estrutura fcc é semicondutor com gap de energia em torno de 1;58 eV, mas quando intercalado com a molecula FeCl3 veri camos que o sistema permanece semicondutor, com gap de 0;68 eV. Já para o sistema CrO3/fcc observamos que este passa a ser metalico. O C60 bcc puro é semicondutor, mas quando intercalado com a molecula FeCl3, o sistema passa a apresentar carater metalico. Enquanto que intercalado com o CrO3, o sistema permanece semicondutor com gap de energia reduzido para 1;20 eV.

In dieser Arbeit habe ich mich hauptsächlich mit der optischen Spektroskopie im sichtbaren bis nahinfraroten Bereich an Akzeptoren für organische bulk-heterojunction Polymer-Fulleren Solarzellen beschäftigt. Dabei führte ich sowohl Untersuchungen an reinen Fullerenproben als auch Gemischen dieser mit Polymeren durch. Ergänzend sind Messungen zur Morphologie, den Spinzuständen und der Solarzellenleistung erfolgt. Erreicht werden sollte, die generelle Eignung neuartiger Akzeptoren für organische Solarzellen festzustellen, die photoinduzierten spektroskopischen Signaturen von optisch angeregten Anionen auf Fullerenen verschiedener Größe zu finden und zu interpretieren sowie zum Abschluss die Abläufe der Ladungsträgergeneration in Polymer:Lu3N@C80 Solarzellen nachzuvollziehen und dadurch die Ursache der vergleichsweise geringen Stromdichte in diesen Zellen zu verstehen, die 25 % geringer ist als in P3HT:PC60BM Solarzellen. Die Ergebnisse sind, dass C70-C70 Dimer Fullerene sehr gute Akzeptoren darstellen, die neben einer etwas besseren Absorption als C60 basierte Akzeptoren im Bereich um 500 nm sehr gute Fähigkeiten als Elektronenakzeptoren zeigen. Die Messung an Fullerenen verschiedener Größe, um Anionensignaturen zu finden, hat deutliche Signaturen für C60- bei 1.18 eV und für C70- bei 0.92 eV erbracht. Weniger einfach zu finden und interpretieren sind die Signaturen von C80- und C84-. Aufgrund der geringen Signalstärke sowie spezieller Eigenheiten der zur Verfügung stehenden Fullerene konnte ich nur einen ungefähren Bereich von 0.7~eV bis 0.4~eV für die Anionensignaturen abschätzen. Allerdings zeigt sich für alle Fullerene eine Rotverschiebung der Anionensignaturen hin zu niedrigeren Energien mit steigender Zahl der Kohlenstoffatome pro Fulleren. Die umfangreichste Untersuchung habe ich an dem Molekül Lu3N@C80 in seiner Funktion als Elektronenakzeptor in P3HT:Lu3N@C80 Solarzellen gemacht. Während das Molekül in Kombination mit P3HT eine hohe Leerlaufspannung von 835 mV erzeugt, ergeben diese Zellen geringere Stromdichten. Mein Ziel war es, die Prozesse zu identifizieren und zu verstehen, die dafür verantwortlich zeichnen. Aus der Kombination verschiedener Messmethoden, ergänzt mit generellen Erkenntnissen zu endohedralen Fullerenen aus der Literatur, ließ es zu, einen intramolekularen Elektronentransfer von den Lutetiumatomen innerhalb des C80 auf das Fulleren als Ursache zu identifizieren. Die in dieser Arbeit gewonnenen Daten liefern weitere Indizien, dass die Verwendung von C70 basierten Fullerenen eine gute Option zur Verbesserung des Wirkungsgrads von organischen Solarzellen sein kann, trotz der höheren Herstellungskosten. Die gefundenen Anionensignaturen auf den Fullerenen bieten einen weiteren Ansatz, die Anregungsabläufe in verschiedenen bulk-heterojunctions über spektroskopische Messungen nachzuvollziehen. Abschließend habe ich mit meinen Messungen an Lu3N@C80 einen generell zu beachtenden Effekt aufgezeigt, der bei der zukünftigen Synthese funktionaler Akzeptoren ähnlicher Art berücksichtigt werden sollte, um eine optimale Leistungsfähigkeit solcher Moleküle zu gewährleisten. Während die Projekte über die Dimer Akzeptoren und das Lu3N@C80 Molekül abgeschlossen wurden, sind bei der Untersuchung der Anionen, speziell auf großen Fullerenen, noch Fragen offen, und es wären zusätzliche Nachweise wünschenswert. Dies könnte mit spinsensitiven und zeitaufgelösten Messmethoden, die am Lehrstuhl vorhanden sind, an den hier schon vorgestellten Materialien erreicht werden. Eine weitere Möglichkeit wäre es zu versuchen, PC81$BM zu bekommen und dies zu untersuchen, auch in Gemischen mit noch mehr verschiedenen Polymeren mittels photoinduzierter Absorption. / The main topic of my thesis was the optical spectroscopy of accepters for organic bulk-heterojunction polymer-fullerene solar cells in the visible till near-infrared regime. Pure fullerene samples as well as blends of fullerenes with polymers were studied. Additionally measurements regarding the morphology, spin states and solar cell performance were done. The aims were to determine the ability of new molecules as acceptors for organic solar cells, to find and understand the photoinduced absorption signatures of optical excited anions on fullerene bulks of different sizes and finally to learn about the charge carrier generation process in polymer:Lu3N@C80 blends and thus understand the origin of the comparable low current density in this devices, about 25 % less than for P3HT:PC60BM solar cells. In our publications due to these topics we presented that the novel C70-C70 dimer fullerenes are fine acceptors for polymer:fullerene solar cells, showing a better absorption coefficient around 500 nm than C60 based acceptors and high singlet-exciton quenching rates. Anion signatures for fullerene molecules of different sizes were clearly found for C60- at 1.18 eV and for C70- at 0.92 eV. Less clear are my findings regarding the signatures for C80- and C84-. Due to the low signal-to-noise ratio in these measurements and some unique properties of the available materials I was only able to indicate a range from 0.7 eV down to 0.4 eV for the optically detected anion signatures of these fullerenes. Still all fullerenes showed a red shift to lower energies for the anion signatures getting stronger the more carbon atoms the fullerenes were made of. The most detailed research in this thesis was done about the Lu3N@C80 molecules application as electron acceptor in P3HT:Lu3N@C80 solar cells. The use of this acceptor in combination with P3HT lead to a high open circuit voltage of 835 mV in the devices produced, but also a rather low current density. I tried to understand the processes in the charge carrier generation and extraction process causing this. Using several measurement techniques, combined with general knowledge about comparable endohedral fullerenes from the literature, I was able to identify an internal charge transfer of electrons from the lutetium atoms encaged in the C80 to the fullerene bulk as origin The results presented in this work give further indications for the advantages of using C70 based fullerene acceptors in organic solar cells to raise the total power conversion efficiencies of these devices, despite the higher production costs. The identification of anion signatures of different fullerenes show an additional method to monitor the excitation processes by optical spectroscopy in bulk-heterojunction devices. My research regarding the Lu3N@C80 molecule showed a general effect regarding this class of molecules, that will be important for any further synthesizes or application of such molecules in organic photovoltaics. While the projects regarding the dimer acceptors and the Lu3N@C80 molecule were completed in this work, the analysis of spectroscopic anion signatures left some open questions, especially for large fullerenes. Further investigations using spin sensitive or time resolved techniques, as available in our research group, could be useful to gather more detailed information on this topic. Also trying to get some PC81BM for photoinduced absorption measurements, alone and in blend with several polymers, might be another way to energetically pinpoint the anion signature on C80.

L'effet photovoltaïque est une des voies qui s'est significativement développée au cours des dernières années afin de trouver une alternative à la production d'énergies non-renouvelables. Afin de diminuer le coût de fabrication de ces dispositifs photovoltaïques, une solution consiste à remplacer le silicium par des matériaux organiques. Les cellules solaires organiques sont une technologie en pleine émergence qui ambitionne la fourniture de cellules solaires plus flexibles dans tous les sens du terme : mécanique, fabrication, propriétés électro-optiques. Un défi auquel la recherche est confrontée aujourd'hui est l'obtention de matériaux organiques stables et solubles qui absorbent aux longueurs d'ondes du proche infrarouge. Ce travail de thèse réalisé dans l'Équipe de Recherche Technologique CSPVP de l'Université d'Angers a pour objectif de relever le défi. La première partie de notre travail est consacrée à l'utilisation de nouveaux dérivés de fullerènes. Afin d'améliorer l'absorption du fullerène C60 ou/et de chercher de possibles alternatives au PCBM, des nouveaux composés ont été synthétisés. Ces nouveaux dérivés peuvent être répartis en: dyades C60-PDI(R=OPhtBu, Cl), cyclopropano[60]fullerènes et cyclopropano[70]fullerènes de type Bingel porteurs de deux groupes esters C60(ou 70)>(CO2R1)(CO2R2), et l'adduit-1,4 C60(CH2CO2tC4H9)2. Ces dérivés de fullerènes ont été incorporés dans les couches photo-actives des cellules solaires à base du polymère conjugué poly(3-hexylthiophène) (P3HT), en tant que matériau de type accepteur. Tous ont été utilisés en cellules solaires pour lesquelles nous avons cherché à préciser la relation entre structure moléculaire et performances photovoltaïques via la morphologie de la couche active. Des études supplémentaires ont été effectuées afin de corroborer les résultats photovoltaïques (PV) avec les propriétés physico-chimiques des matériaux. La deuxième partie est consacrée à des études physico-chimiques réalisées sur des différents nanotubes de carbones mono-feuillets (SWCNT) fonctionnalisés par des groupements esters. Ces nanotubes fonctionnalisés présentent une meilleure dispersion dans les solvants organiques. Ils ont été étudiés et comparés à différentes concentrations dans des cellules solaires à base de P3HT :PCBM. Des travaux complémentaires ont été effectués sur des dérivés de poly(phénylène vinylène) (PPV) et des dérivés de polythiophène, et des cellules élaborées à partir de dérivés de carbazole attaché sur le noyau de C60 et déposés sur des substrats ITO/PEDOT :PSS par électropolymérisation. En conclusion, nous passons en revue les paramètres qui contribuent directement aux performances photovoltaïques des cellules étudiées.

<p>The urgent need for new, sustainable energy source intrigues scientists to provide the solution by developing new technology. Polymer solar cell appears to be the most promising candidate for its low cost, flexibility, and massive producibility. Novel polymers have been constantly synthesized and investigated, while the use of PCBM as acceptor seems to be the universal choice. Here, we studied the use of four dierent fullerene derivatives - [60]PCBM, [70]PCBM, and their bisadduct analogues - as acceptor in APFO-3 solar cells. A series of investigations were performed to study how the processing parameters - blend ratio, spin speed, and choice of solvent - influence the device performance. Using bisadduct fullerenes results in an enhanced Voc, as predicted by the up-shift of energy levels, but a strongly reduced Jsc, hence a poor PCE. Photoluminescence study indicates that all APFO-3:fullerene devices are limited by the inefficient dissociation of fullerene excitations, while it becomes more influential when bisadduct fullerenes were used as acceptor. The best device in this study was fabricated by using [70]PCBM as acceptor and chlorobenzene as solvent, exhibits a PCE of 2.9%, for the strong absorption, ne morphology, and comparatively strong driving force.</p>

<p>Crystallization of C₆₀ and C₇₀ from organic solution often leads to the formation of new solvates and other fullerene compounds. In the present thesis, a number of such solvates were obtained and their phase transitions studied using <i>in situ</i> "in solution" techniques. New fullerene materials can be also obtained using High Pressure High Temperature (HPHT) treatment. The formation of C₆₀ polymers in thin films and bulk samples has been studied in situ over a wide pressure-temperature range.</p><p>New methods for single-crystal growth of fullerenes and their compounds have been developed. It was found by <i>in situ</i> "in solution" XRD and Raman spectroscopy that solvate C₆₀ crystals with benzene, toluene and hexane are stable only in equilibrium with their solution. Their melting points coincide with the maximum in the temperature dependence of solubility. C₇₀ solvates grown from these solutions are stable out of solution, and decompose above the boiling points of the solvents. Vibrational signatures were found for the C₆₀ and C₇₀ solvates which are very similar to these for fullerene-sulfur compounds obtained as thin films and single crystals. A new C₇₀S₈ compound was obtained as relatively large single crystals. </p><p>C₆₀ polymerisation under HPHT conditions was studied on thin films and showed a thickness effect on the phase transition around 20 GPa. Superhard and superelastic films were obtained by treatment at 23 GPa and 570K. In situ Raman and XRD studies were performed on bulk samples at pressures up to 27 GPa and temperatures up to 850K. Below 13 GPa, only one- and two-dimensional polymers were found to form during the heating. The observed polymerisation pathway suggests a gradual increase in polymerisation. Above 18 GPa, the <i>in situ</i> Raman spectra obtained during heating remained almost unchanged. The XRD study showed that heating at 830K and 13 GPa leads to the formation of a rhombohedral phase with a volume per C₆₀ molecule of 560-570 ų/M, which is below the value for two-dimensional polymers. Nevertheless, no superhard, highly dense phases were observed under these conditions, in contrast to previous studies.</p>

<p>In this thesis, the preparation of new photoactive substances containing mono- and bipyridines coordinated to ruthenium is presented together with initial evaluations of their photoelectrochemical and photophysical properties. </p><p>Complexes of the type Ru(bpy)₂(4-X-py)₂ (X = SH, COOH) were prepared and used in Grätzel-type solar cells based on ZnO. The results show that the thiol complex binds to the surface but give rather low solar cell efficiencies. Different routes to obtain Ru(bpy)₂(4,4´-dithio-2,2´-bipyridine) were evaluated, among them substitution reactions on 4,4´-dichloro-2,2´-bipyridine coordinated to ruthenium. Due to reactivity issues, the target sulphur-containing complex has not yet been obtained.</p><p>The synthesis of methanofullerenes, fulleropyrrolidines and –pyrazolines are presented, among them dyads containing Ru(bpy)_n-units. A common feature for the dyads is the unusually short linkers between the fullerene and the ruthenium complex. Dyad preparations were in some cases simplified by carrying out the reactions in the presence of silver salts.</p><p>A preliminary evaluation of the emission of the dyads showed almost complete quenching of the excited state of a pyrrolidine-based dyad, whereas emission remained from the pyrazoline-based ones. Whether this was due to incomplete quenching of the excited states of the ruthenium complex, or induced by the presence of hydrazones has yet to be revealed.</p><p>The use of fullerene-substituted malonic acid and its ethyl ester as dyes in Grätzel-type solar cells resulted in even lower efficiencies (IPCE) than for bare TiO₂. This could be due to electron transfer in the reverse direction compared to what is observed for ruthenium complexes. Thus, these fullerene derivatives are not suitable as sensitisers for Grätzel-type solar cells.</p>

Crystallization of C60 and C70 from organic solution often leads to the formation of new solvates and other fullerene compounds. In the present thesis, a number of such solvates were obtained and their phase transitions studied using in situ "in solution" techniques. New fullerene materials can be also obtained using High Pressure High Temperature (HPHT) treatment. The formation of C60 polymers in thin films and bulk samples has been studied in situ over a wide pressure-temperature range. New methods for single-crystal growth of fullerenes and their compounds have been developed. It was found by in situ "in solution" XRD and Raman spectroscopy that solvate C60 crystals with benzene, toluene and hexane are stable only in equilibrium with their solution. Their melting points coincide with the maximum in the temperature dependence of solubility. C70 solvates grown from these solutions are stable out of solution, and decompose above the boiling points of the solvents. Vibrational signatures were found for the C60 and C70 solvates which are very similar to these for fullerene-sulfur compounds obtained as thin films and single crystals. A new C70S8 compound was obtained as relatively large single crystals. C60 polymerisation under HPHT conditions was studied on thin films and showed a thickness effect on the phase transition around 20 GPa. Superhard and superelastic films were obtained by treatment at 23 GPa and 570K. In situ Raman and XRD studies were performed on bulk samples at pressures up to 27 GPa and temperatures up to 850K. Below 13 GPa, only one- and two-dimensional polymers were found to form during the heating. The observed polymerisation pathway suggests a gradual increase in polymerisation. Above 18 GPa, the in situ Raman spectra obtained during heating remained almost unchanged. The XRD study showed that heating at 830K and 13 GPa leads to the formation of a rhombohedral phase with a volume per C60 molecule of 560-570 Å3/M, which is below the value for two-dimensional polymers. Nevertheless, no superhard, highly dense phases were observed under these conditions, in contrast to previous studies.

In this thesis, the preparation of new photoactive substances containing mono- and bipyridines coordinated to ruthenium is presented together with initial evaluations of their photoelectrochemical and photophysical properties. Complexes of the type Ru(bpy)2(4-X-py)2 (X = SH, COOH) were prepared and used in Grätzel-type solar cells based on ZnO. The results show that the thiol complex binds to the surface but give rather low solar cell efficiencies. Different routes to obtain Ru(bpy)2(4,4´-dithio-2,2´-bipyridine) were evaluated, among them substitution reactions on 4,4´-dichloro-2,2´-bipyridine coordinated to ruthenium. Due to reactivity issues, the target sulphur-containing complex has not yet been obtained. The synthesis of methanofullerenes, fulleropyrrolidines and –pyrazolines are presented, among them dyads containing Ru(bpy)n-units. A common feature for the dyads is the unusually short linkers between the fullerene and the ruthenium complex. Dyad preparations were in some cases simplified by carrying out the reactions in the presence of silver salts. A preliminary evaluation of the emission of the dyads showed almost complete quenching of the excited state of a pyrrolidine-based dyad, whereas emission remained from the pyrazoline-based ones. Whether this was due to incomplete quenching of the excited states of the ruthenium complex, or induced by the presence of hydrazones has yet to be revealed. The use of fullerene-substituted malonic acid and its ethyl ester as dyes in Grätzel-type solar cells resulted in even lower efficiencies (IPCE) than for bare TiO2. This could be due to electron transfer in the reverse direction compared to what is observed for ruthenium complexes. Thus, these fullerene derivatives are not suitable as sensitisers for Grätzel-type solar cells.

The urgent need for new, sustainable energy source intrigues scientists to provide the solution by developing new technology. Polymer solar cell appears to be the most promising candidate for its low cost, flexibility, and massive producibility. Novel polymers have been constantly synthesized and investigated, while the use of PCBM as acceptor seems to be the universal choice. Here, we studied the use of four dierent fullerene derivatives - [60]PCBM, [70]PCBM, and their bisadduct analogues - as acceptor in APFO-3 solar cells. A series of investigations were performed to study how the processing parameters - blend ratio, spin speed, and choice of solvent - influence the device performance. Using bisadduct fullerenes results in an enhanced Voc, as predicted by the up-shift of energy levels, but a strongly reduced Jsc, hence a poor PCE. Photoluminescence study indicates that all APFO-3:fullerene devices are limited by the inefficient dissociation of fullerene excitations, while it becomes more influential when bisadduct fullerenes were used as acceptor. The best device in this study was fabricated by using [70]PCBM as acceptor and chlorobenzene as solvent, exhibits a PCE of 2.9%, for the strong absorption, ne morphology, and comparatively strong driving force.

Fullerene research has advanced to elevated levels in a short period of time due to the unique chemical and physical properties of the caged molecule that have been utilized in numerous applications. Due to the spherical shape of the fullerene molecule which allows for a hollow cavity, encapsulation of atoms or small molecules can occur within the ball structure. This encapsulation creates an endohedral component that is limited from interacting with other molecules which creates potential of control over electronic information of the isolated molecule. Endohedral fullerenes have the potential as serving as the base unit in a quantum computer if control over global alignment is attained. Thus, by using the inherent self-assembling capabilities of some organic materials, ordered endohedral fullerenes can be achieved. This dissertation investigates the ability to use self-assembling strategies to obtain alignment which include ordering within a morphologically controlled copolymer matrix, forming a supramolecular polymer complex with cyclodextrin, and encapsulation within the helical wrap of polymer chains. The ultimate goal is to understand the dynamics that control association and orientation of varying fullerene-based molecules in each strategy in order to maximize control over the final alignment of endohedral elements.