Orientadores: Vitor Baranauskas, Ana Flavia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-12T11:11:13Z (GMT). No. of bitstreams: 1 Valente_GustavoMonteirodaSilva_M.pdf: 2272217 bytes, checksum: c82b3f59d489a35f76f4e4d2a2263828 (MD5) Previous issue date: 2008 / Resumo: Novas fontes de energia limpa de baixo custo devem ser obtidas nas próximas décadas para sustentar o consumo de energia mundial e manter o meio-ambiente livre de gases de efeito estufa. Enquanto células solares inorgânicas são uma fonte limpa de energia, essa tecnologia é restrita devido a seu alto custo de produção. Células solares orgânicas têm sido desenvolvidas para solucionar este problema, pelo menos para dispositivos pequenos, isto é, para aplicações de baixa corrente. Recentemente novos materiais tal como polímeros condutores e nanotubos de carbono vêm sendo utilizados em células solares orgânica de heterojunção. Uma célula solar eficiente deve absorver toda (ou boa parte) da luz solar e gerar e transportar portadores de carga livre para seus eletrodos para assim produzir corrente elétrica e um potencial interno. Neste trabalho usamos o polímero poli[2-methoxy-5-[(3,7-dimethyloctyloxy) phenylene vinylene] (MDMO-PPV) como material absorvedor e transportador de buracos e nanotubos de carbono para dissociação do exciton e tranporte de elétrons. A morfologia e foto-fisica das células, bem como a caracterização do dispositivo é estudada. / Abstract: New sources of low cost and clean energy must be achieved in the coming decades to sustain world consumption while also keeping the environment free of green house gases. While inorganic solar cells are a source of clean energy, they are plagued by high production costs. Organic solar cells have been developed as a solution to this problem as a means to harvest light while keeping production costs low. Recently, new materials such as conductive polymers, carbon nanotubes (CNT) and fullerenes have been utilized in bulk heterojunction organic solar cells1,2. Increasing the effi-ciency of these organic solar cells is crucial for them to become economically viable. An efficient solar cell must harvest all the possible light from the Sun and produce and transport free charges carriers to their electrodes to produce electrical current with a built-in potential. In this work we use a poly[2-methoxy-5-[(3,7-dimethyloctyloxy) phenylene vinylene] (MDMO-PPV) as the absorption and hole transport material and CNT for exciton dissociation and electron transport. The morphology and photophysics of the films, as well as the characteristic J-V curves for the devices were obtained. / Mestrado / Eletrônica, Microeletrônica e Optoeletrônica / Mestre em Engenharia Elétrica

Les cellules solaires organiques sont une technologie très prometteuse grâce à leur faible-coût de fabrication, leur flexibilité et leur légèreté. Actuellement, elles ne sont qu’au stade du prototype à cause de leurs faibles rendements et leur courte durée de vie. L’une des voies les plus étudiées pour améliorer le rendement est la conception de nouveaux matériaux photo-actifs. Lors de cette thèse, deux séries de semi-conducteurs donneurs d’électrons. La première série comprend trois oligomères, chacun composé de trois unités de diketopyrrolopyrrole (DPP) qui est un chromophore très étudié dans la littérature. Ces oligomères ont la particularité d’absorber dans le proche infra-rouge. En intercalant différents groupements donneurs d’électrons entre les DPPs, différentes torsions sont obtenues le long de leur squelette. Ceci a permis d’établir qu’un oligomère plan a une plus grande cristallinité et par conséquent transporte mieux les charges, atteignant une mobilité de trou de 10-3 cm². V-1.s-1. Cependant, cette forte cristallinité entraîne une hétérojonction volumique défavorable et un faible rendement photovoltaïque (<1%). La deuxième série est composée de quatre petites molécules combinant une unité 3,3’-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI) avec différents groupements donneurs d’électrons: thiophène (EBI-T), benzofurane (EBI-BF) and bithiophène (EBI-2T)). Les dérivés EBI ont été testés dans les transistors à effet de champ et dans les cellules solaires en tant que semi-conducteurs donneurs. La meilleure mobilité de trou de 0,021 cm².V-1.s-1 a été mesurée avec EBI-BF grâce à sa conformation plane alors que le PCE maximal de 1.92% est obtenu avec EBI-2T grâce à son large spectre d’absorption et une morphologie adéquate. / Organic solar cells appear as a promising technology within photovoltaic field owing to their low-cost fabrication and their great flexibility enabling a widespread distribution. For now, they are still at the prototype stage due to their limited efficiency and lifetimes. Many efforts were realized in designing new materials as they are involved in every steps of the photovoltaic process and thus they dictate the cell efficiency. Along this thesis, two series of electron-donating semi-conductors were designed and synthesized. The first series consist in three oligomers containing three diketopyrrolopyrrole units, a well-studied chromophore. Those oligomers absorb up to the near infra-red region, a very interesting feature for light harvesting. Through the engineering of electron-rich spacers, various twists were generated in the oligomers backbone. The oligomer showing a coplanar conformation appears to be the most crystalline and thus exhibits the best charge transport properties with a hole mobility of 10-3 cm².V-1.s-1.iiiHowever, bulk heterojunction organic solar cells, this high crystallinity results in an unfavorable morphology and a PCE inferior to 1%. As for the second series, the four small molecules combined 3,3’-(ethane-1,2-diylidene)bis(indolin-2-one) (EBI), an electron deficient unit, and various electron-rich units such as thiophene (EBI-T), benzofuran (EBI-BF) and bithiophene (EBI-2T). Among EBI derivatives, EBI-BF demonstrated the highest hole mobility of 0.021 cm².V-1.s-1 in field effect transistors due to its coplanar conformation. Meanwhile, in bulk heterojunction solar cells, the highest PCE of 1.92% was obtained with EBI-2T:PC61BM blend owing to a more appropriate morphology and the broadest absorption spectrum of EBI-2T.

For its inherent advantages, such as lightweight, low cost, flexibility, and opportunity to cover large surface areas, organic solar cells have attracted more and more attention in both academia and industry. However, the efficiency of organic solar cell is still much lower than silicon solar cells, but steadily rising as it now stands above 8%. The architecture of bulk heterojunction solar cells can improve the performance of organic solar cell a lot, but these improvements are highly dependent on the morphology of photoactive layer. Therefore, by controlling the morphology of photoactive layer, most commonly composed of a P3HT donor polymer and PCBM small molecule, the performance of organic solar cells could be optimized. The use of solvent additives in the solution formulation is particularly interesting, because it is a low cost method of controlling the phase separation of the photoactive layer and possibly removing the need for subsequent thermal and solvent vapor annealing. However, the role of the solvent additive remains not well understood and much debate remains on the mechanisms by which it impacts phase separation. In the first part of this thesis, we investigate the role of the solvent additive on the individual components (solvent, donor and acceptor) of the solution and the photoactive layer both in the bulk solution, during solution-processing and in the post-processing solid state of the film. In the second part of this thesis, we investigate the role of the additive on the blended solution state and resulting thin film phase separation. Finally, we propose a new method of controlling phase separation based on the insight into the role of the solvent additive. In the first part, we used an additive [octandiethiol (OT)] in the solvent to help the aggregation of P3HT in the solution. From the UV-vis experiments, the crystallinity of P3HT in the solutions increased while it decreased in thin films with steady increase of additive concentration. This method could be used for one step, annealing-free fabrication of organic solar cell with high performance. The solution can potentially be used to prepare ink for the large scale roll-to-roll ink-jet printing of P3HT thin films. Secondly, from the experiments it is found that differences in the evaporation rate and solubility of the components of the photoactive layer may be part of the reason for morphological changes. With lower evaporation rate than the host solvent, the additive concentration in the solution keeps increasing with time during the final stages of spin coating. In addition, the phase separation is increased with the increase of additive concentration, as demonstrated by AFM and TEM. By controlling the additive concentration, it is possible to control the phase separation of photoactive layer in pristine device. It is also found that the additive can change the wetting ability of the solvent to produce films with high surface coverage. With this information in hand, we modified the solution process of BHJ layers. A layer of crystals was deposited from the OT-containing solution by postponing the start of the spin coating for several minutes (delay time) after the solution is dropped on the surface of substrate. We found this to be a very effective method of increasing the phase separation and crystallinity of the photoactive materials. This effect was not possible when using oDCB solvent without any additive.

The evolution of the internet of things (IoT) opens the market opportunity for organic photovoltaic cells, especially for indoor applications where the lifetime of the organic cells is longer than outdoor. For example, IoT requires off-grid energy sources for many devices with low power consumption. In this work, new materials were tested as candidate components in the active layer of printed organic photovoltaics by fabrication of devices. The initial electrical performance of these devices and their stability over time were investigated by measurements of the current-voltage characteristics. Three selected active layers were further investigated with atomic force microscopy (AFM) measurements. The current-voltage measurements showed that the addition of a solvent additive to the active layer ink affects the initial electrical performance as well as the stability of the devices. The AFM measurements showed that the surface topography of the active layer was affected by the sort of solvent additive that was used. Three new electron acceptor material and two solvent additives showed promising electrical performance and stability.

Organic solar cells are one of the most promising candidates for future solar power generation. They are thin and lightweight with several additional advantages such as scalability, environmental sustainability and low cost for processing and installation. However, the low charge carrier mobility of the absorbing material for organic solar cells requires thin absorber layers, limiting photon harvesting and the overall power conversion efficiency. Several attempts, e.g., periodically patterned structures and scattering layers have been tried to enhance the absorption of thin-film solar cells as light trapping elements. However, much effort is required to introduce light trapping structures to conventional rigid metal oxide electrodes and glass substrate. For instance, almost 13 hours are required to fabricate micro structures of 1 m2 area on glass, in contrast, 1 minute on PET using a same laser set-up and an additional scattering layers are demanded for providing light trapping effects to solar cells. In the last years, flexibility is emerging as the one of the major advantages of organic solar cells. To realize flexibility of solar cells, the classically used glass substrates and ITO electrodes are too brittle. Therefore, polymer materials are promising candidates to replace them as flexible electrodes and substrates. In this thesis, the highly transparent conducting polymer, PEDOT:PSS and PET equipped with an AlOx encapsulation layer are used as electrode and substrate, respectively. Besides the flexibility, additional light trapping elements, e.g. scattering particles, nano- and microstructures can be easily applied to the polymer materials since they have the potential for easier shaping and processing. In this study, we apply different light trapping and in-coupling approaches to organic solar cells. First, PET substrates are structured with a direct laser interference patterning system, which is a powerful and scalable one-step technique for patterning polymers. Almost 80 % of the light is diffracted by these patterned PET substrates and thereby the light path in the absorption layer is increased. Optical display films, commercially developed to be used as back light units of liquid crystal displays are also examined as light trapping substrates and exhibit similar enhancement as patterned PET. Moreover, since PEDOT:PSS is prepared by a solution-based process, TiO2 nanoparticles are added as light scattering elements to the PEDOT:PSS electrodes. Consequently, those electrodes provide a dual function as electrical contact and light trapping element. Finally, 2- or 3-dimensional nanostructures are printed by a nano-imprinting technique onto the surface of PEDOT:PSS with PDMS stamps. By controlling the temperature and the time of PEDOT:PSS during an annealing step, nanostructures are transferred from PDMS masks to PEDOT:PSS. To evaluate the effects of light trapping for all above mentioned approaches, flexible organic solar cells are produced by vacuum evaporation using blends of DCV5T-Me and C60 as absorber layer. The substrates are optically characterized using UV-vis spectrometer and goniometer measurements. The topography of the samples is measured by atomic force microscopy, scanning microscopy and optical microscopy. Bending tests with various radii are performed to test the flexibility of the substrates. In summary, light trapping effects are successfully implemented in the electrodes and substrates for OPVs, giving efficiency improvements of up to 16 %. The light trapping mechanisms in our approaches are extensively discussed in this thesis. / Organische Photovoltaik ist einer der vielversprechendsten Kandidaten für die zukünftige Solarstromgewinnung auf flexiblen Substraten. Um diese Flexibilität zu ermöglichen, sind herkömliche Glassubstrate mit ITO-Elektroden zu spröde. Ein vielversprechender Kandidat, um sowohl flexible Elektroden als auch flexible Substrate herzustellen, sind Polymere, da diese sehr biegsam und leicht zu verarbeiten sind. Deshalb wird in dieser Arbeit das hoch transparente, leitfähige Polymer PEDOT:PSS als Elektrode und PET (mit einer AlOx Verkapselungsschicht) als Substrat untersucht. Aufgrund der guten Prozessierbarkeit der Polymere konnten wir zusätzlich zu den eigentlichen Funktionen des Substrates und der Elektrode noch den Mechanismus des Lichteinfangs hinzufügen. Zusätzlich zu ihrer Flexibilität haben organische Solarzellen noch weitere Vorteile: sie sind dünn, leicht, skalierbar und verursachen vergleichsweise geringe Kosten für Herstellung und Installation. Ein Nachteil organischer Solarzellen ist die vergleichsweise geringe Ladungsträgerbeweglichkeit der Absorbermaterialien, welche oft die Schichtdicke der Absorbermaterialien begrenzt. Dies hat weniger absorbierte Photonen, weniger Stromdichte und somit einen geringeren Wirkungsgrad zur Folge. In den letzten Jahren wurden periodisch strukturierte Substrate und streuende Schichten als Lichteinfangelemente eingesetzt, um den Wirkungsgrad organischer Solarzellen mit dünnen Absorberschichten zu erhöhen. Gestaltungsregeln für solche Lichteinfangelemente sind noch weitestgehend unbekannt. Im Rahmen dieser Arbeit strukturieren wir PET Substrate mit einem direkten Laserinterferenzsystem, welches ein leistungsfähiges, skalierbares Einschrittverfahren zur Polymerstrukturierung ist. Da PEDOT:PSS aus der Lösung prozessiert wird, können wir weiterhin Nanopartikel hinzufügen, die der Elektrode zusätzlich noch lichtstreuende Eigenschaften geben. Außerdem können 2- bzw. 3-dimensionale Nanostrukturen leicht mithilfe einer Stempeltechnik eingeprägt werden. Um die Effekte des Lichteinfangs, welcher durch die oben genannten Methoden erzeugt wird, zu untersuchen, werden flexible organische Solarzellen mittels Vakuumverdampfung prozessiert. DCV5T-Me und C60 bilden dabei die photoaktive Schicht. Somit werden die Licht fangenden Eigenschaften dieser flexiblen Solarzellen ausgenutzt und ausführlich in der Arbeit diskutiert.

Renewable energy is required for a sustainable future and one way to meet this is with organic solar cells (OSCs). The OSC can be easily manufactured at a low cost, be lightweight and be used on flexible surfaces. If the efficiency in high illumination intensities and stability in harsh environments increase for OSCs, they can com- pete with the other technologies even in outdoor conditions. Another advantage of OSCs is their good performance under low-light and indoor conditions. This is utilized by Epishine, a Swedish company based in Linköping working with small, thin and flexible organic printed solar cells optimized for indoor applications. The goal of this thesis is to determine how Epishine’s solar cells for low-light indoor usage work in more challenging conditions and to identify which are the factors that are detrimental for the lifetime of the cells. The result showed that all modules had a similar initial electrical performance which indicates that the modules have high reproducibility and degradation in darkness is negligible (since the initial measurements were made at different times). The tests showed that the temperature affected the modules. The test in the oven showed a little less than half the degradation compared to tests under the solar simulator, although both tests were subjected to the same temperature. The hu- midity test and the test exposed to LED-light showed almost no degradation. For the levels exposed to the sun or simulated sunlight, the decrease of the short circuit current density shows a burn-in time, which is typical for organic solar cells. After the first couple of hours, the decrease slows down to a more linear behaviour. All modules that were exposed to bright light also showed some recovery effect for short circuit current density and efficiency after they have been kept in the dark. It would be interesting to investigate the behaviour of the modules after even more exposure and look into how the recovery effect works.

>Magister Scientiae - MSc / Environmentally friendly photovoltaic devices make use of solar radiation as the energy source to generate electricity. Organic solar cells (OSCs) have been making headway in the last decade due to their cost-effectiveness and potential application in flexible devices. One of the disadvantages of OSCs is the short lifetime of the charge carriers, where the various interfaces that are present in the material play a significant role. In the inverted organic solar cell (IOSC), electrons are injected into the transparent conducting oxide, whereby the electrode alignment is reversed compared to the conventional structure. Nanosized zinc oxide (ZnO) thin-films with nanoridges/ripples embedded on the surface of the thin-film can be used as an electron transport/hole-blocking layers in inverted organic solar cells to enhance light-capturing by the active layer of the solar cell.

京都大学 / 0048 / 新制・課程博士 / 博士(エネルギー科学) / 甲第17911号 / エネ博第283号 / 新制||エネ||59(附属図書館) / 30731 / 京都大学大学院エネルギー科学研究科エネルギー基礎科学専攻 / (主査)教授 佐川 尚, 教授 八尾 健, 教授 石原 慶一 / 学位規則第4条第1項該当 / Doctor of Energy Science / Kyoto University / DGAM

京都大学 / 0048 / 新制・課程博士 / 博士(工学) / 甲第19007号 / 工博第4049号 / 新制||工||1623(附属図書館) / 31958 / 京都大学大学院工学研究科高分子化学専攻 / (主査)教授 伊藤 紳三郎, 教授 赤木 和夫, 教授 辻井 敬亘 / 学位規則第4条第1項該当 / Doctor of Philosophy (Engineering) / Kyoto University / DFAM

No description available.