Orientadores: Francisco das Chagas Marques, Ana Flávia Nogueira / Dissertação (mestrado) - Universidade Estadual de Campinas, Instituto de Física Gleb Wataghin / Made available in DSpace on 2018-08-26T08:45:20Z (GMT). No. of bitstreams: 1 Coutinho_NataliadeFaria_M.pdf: 12394800 bytes, checksum: 1d28bb92259a5c9eb6848a0fe678b6b3 (MD5) Previous issue date: 2014 / Resumo: A demanda mundial de energia elétrica tem crescido muito nas últimas décadas, o que tem levado a uma busca mais expressiva por fontes de energia renováveis e sustentáveis. Deste modo, as células solares, que através do efeito fotovoltaico convertem a energia proveniente do sol em energia elétrica, tem ganhado atenção. Dentre os vários tipos de células solares, se encontram as células solares sensibilizadas por corante, DSSC, que têm ganhado interesse de estudiosos da área por apresentarem uma possibilidade de geração de energia elétrica a baixo custo. Para que essas células ganhem competitividade no mercado, é necessário que suas eficiências aumentem, e é nesse ramo de pesquisa que o presente trabalho se coloca. Este trabalho foi baseado no estudo e otimização da eficiência de células solares sensibilizadas por corante, onde verificamos a influência de vários fatores na eficiência das células. Dentre eles, se encontram o processo de manufatura das células, o pós-tratamento de TiCl4 sobre o filme nanoestruturado de TiO2, a composição da pasta de TiO2 e do eletrólito líquido, o método de deposição da Pt no contra-eletrodo, e a utilização de uma camada espalhadora de luz com nanopartículas de TiO2 da ordem de 200nm. Além disso, um estudo a respeito do efeito de uma blocking layer de TiO2 entre o FTO e o filme nanoestruturado de TiO2, depositada pela técnica conhecida como atomic layer deposition, ALD, também foi realizado, o que levou a um aumento na eficiência das células. Através desses estudos, conseguimos aumentar a eficiência das células em até 90% se comparado às primeiras células que produzimos (de 3,9% a 7,4%), atingindo valores de tensão de circuito aberto Voc, densidade de corrente de curto-circuito Jsc, fator de preenchimento FF e eficiência ? de até 0,71V, 14,38mA/cm2, 0,67 e 7,4%, respectivamente. Deste modo, uma melhora significativa na performance das células foi observada, chegando a resultados comparáveis aos obtidos por diversos grupos de pesquisa em todo o mundo / Abstract: World demand for electricity has grown in the last decades, which has led to a more expressive search for renewable and sustainable energy sources. Consequently, solar cells have been getting attention because of their capacity to convert energy from the sun into electrical energy through the photovoltaic effect. Among the various types of solar cells, there are the dye-sensitized solar cells, DSSC, which have gained interest of the solar cell community for having a possibility of power generation at low cost. In order to these cells get market competitiveness, it is necessary to increase their efficiency, and this is the research field that the present work is placed into. This thesis was based on the study and optimization of dye-sensitized solar cells efficiency, where we could see the influence of various factors in cells efficiency. Among these, there are the cells manufacturing process, the post-treatment on nanostructured TiO2 films using a TiCl4 solution, the composition of the TiO2 paste and the liquid electrolyte, the method of Pt deposition at the counter electrode, and the use of a reflecting layer with 200nm TiO2 nanoparticles. In addition, a study of the effect of a TiO2 blocking layer between the FTO and the nanostructured TiO2 film deposited by the technique known as atomic layer deposition, ALD, was also performed, which led to an increase in cells efficiency. Through these studies, we could increase cells efficiency by up to 90% compared to the first cells we produced (from 3,9% to 7,4%), reaching values of open circuit voltage Voc, short circuit current density Jsc, fill factor FF and efficiency _ of up to 0,71V, 14,38mA/cm2, 0,67 and 7,4%. Thus, a significant improvement in cells performance was observed, reaching results comparable to that obtained by many research groups around the world / Mestrado / Física / Mestra em Física

Actuellement, le secteur des nanotechnologies est en développement intense. Les nanoparticules de dioxyde de titane et d¿or occupent une part importante de ce secteur, avec des applications utilisant principalement leurs propriétés optiques et catalytiques. Les synergies pouvant exister entre les nanoparticules d¿or et leur support, en particulier via l¿effet plasmon, permettent de modifier la réponse optique de dispositifs catalytiques ou photovoltaïques. Une nouvelle technique polyvalente de mise en forme de film mésoporeux à base de nanoparticules de dioxyde de titane et d¿or a été développée. L¿utilisation de différentes méthodes de synthèse des nanoparticules a permis le contrôle de la morphologie et des propriétés physiques des films déposés par centrifugation. Finalement, l¿adéquation de ces films à leur utilisation en tant qu¿anode de cellules solaires à colorant a été évaluée. / Nanotechnologies represent a fast growing market. Gold and titanium dioxide nanoparticles are an important part of this market, thanks to their optical and catalytic properties. Existing synergies between gold nanoparticles and their substrate, mainly via the plasmonic effect, allow modifying the optical response of catalytic and photovoltaic systems. A new versatile approach is proposed to form mesoporous nanostructures composed of gold and titanium dioxide nanoparticles. The use of various syntheses allowed the formation of nanoparticles leading to a good control upon aggregation morphology and physical properties of centrifuged films. Finally, appropriateness of these films for a use as dye sensitized solar cell anodes was evaluated.

Dye sensitized solar cells (DSSCs) are an attractive way to convert light into electricity. Its development requires a detailed understanding and kinetic optimization of various electronic processes, especially those occurring at the mesoporous TiO2/dye/electrolyte interface. This dissertation work is focused on the exploration of the various electronic processes at the sensitized-electrode/electrolyte interface by using various electrochemical and photochemical methods. Firstly, an alternative redox couple—TEMPO/TEMPO·+ with a relatively high positive redox potential—is explored, aiming to reduce the energy loss during the dye regeneration process. Despite the fast dye regeneration, the charge recombination between the electrons in the conduction band of mesoporous TiO2 and the oxidized redox species is found to be the limiting factor of the device. Further, a more efficient tandem-electrolyte system is developed, leading to DSSCs with the power conversion efficiency of 10.5 % and 11.7 % at 1 sun and 0.5-sun illumination, respectively. An electron-transfer cascade process during dye regeneration by the redox mediators is discovered to be beneficial. Further stability studies on the device suggest the crucial role of TiO2/dye/electrolyte interfaces in the long-term stability of cobalt bipyridyl electrolyte-based DSSCs. On the fundamental level, the local electric field and Stark effects at the TiO2/dye/electrolyte interface are investigated in various aspects—including the charge compensation mechanism, the factors affecting the electric field strength, as well as its impact on charge transfer kinetics. These results give further insights about the TiO2/dye/electrolyte interface, and contribute to the further development and understanding of DSSCs.

Dye-sensitized solar cells (DSSCs) or Grätzel cells are electrochemical devices in where physicochemical properties of different materials are combined to obtain electric energy. These photoconversion devices have evolved from a pioneering concept of molecular photovoltaics to industrial development with confirmed record efficiencies of 14.3%. Their efficiency combined with low-cost production methods and a high aesthetic interest enables the production of DSSC products for consumer electronics market. The strengths of this technology and the fact that its drawbacks are not limiting for this application makes consumer electronics and DSSC a perfect match for the development of self-powered devices. Some companies have already spot a potential market and are currently launching different consumer electronics and other devices with embedded DSSC. This thesis provides an overview of the operation principles of DSSC and the possible routes to improve the efficiency of these devices to emerge and thrive. Additionally, improvements in efficiency, stability and manufacturing needed to be addressed in the near future for this technology are discussed and its suitability to represent a breakthrough in the market of consumer electronics. An overview of the main companies developing DSSC and current prototypes and products is included.

This work studies the subject of perovskite solar cells. The structure of perovskites is described along with a portion of photovoltaics history that led to the employment of perovskites as absorpsion layers. Further, methods of measurement for solar cells such as impedance spectroscopy, photospectroscopy and load characteristics are summarized. Lastly there is a description of already done analytics of perovskite solar cells with the summary of the results. In the practical part, there are measurements made to find out any effect of cell topology or light source wavelength on the cell performance.

MSc (Physics) / Department of Physics / Currently the dye sensitized solar cells have attracted more attention due to their low cost, transparency and flexibility. These types of solar cells use the dye molecule adsorbed on TiO2 semiconductor in Nano architecture with the role of absorbing photons, in recent research attempts are being made to shifts the absorption spectral of TiO2 to visible and near infrared–region of solar spectrum to achieve maximum photo absorption which yields to an increase in the efficiency of the dye sensitized solar cells. In the current study, density functional theory (DFT) was used to model two croconate dyes (CR1 and CR2), one with an electron donating methyl group (CR1) and the other with an electron –withdrawing caboxyl group (CR2). The geometric, electronic and optical properties of these dyes were compared. The adsorption behaviour of the two dyes on (010 and 100) anatase TiO2 surfaces were investigated in this study by employing first principle calculation based on DFT using a plane-wave pseudo potential method. The generalized gradient approximation (GGA) was used in the scheme of Perdew-Burke Ernzerhof to describe the exchange -correlation function as implemented in the CASTEP package in Material Studio of BIOVIA. The adsorption results shows a spontaneous electron injection followed by efficient regeneration of the oxidized dye molecules by the electrolyte and strong binding ability of CR2 to the TiO2 surface, but also shows a comparable binding strength of CR1. The results of this study will help in the design of high efficient dye for DSSCs. / NRF

京都大学 / 0048 / 新制・課程博士 / 博士(理学) / 甲第20657号 / 理博第4322号 / 新制||理||1621(附属図書館) / 京都大学大学院理学研究科化学専攻 / (主査)教授 寺西 利治, 教授 島川 祐一, 教授 小野 輝男 / 学位規則第4条第1項該当 / Doctor of Science / Kyoto University / DGAM

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Modern civilization highly depends on energy and finding alternative sources to fossil fuels becomes more and more necessary. The sun is the most abundant energy source available and exploiting it efficiently would result in a great environmental and economic breakthrough. Among the photovoltaic devices, dye-sensitized solar cells (DSCs) emerged for their tremendous commercial potential deriving from a combination of low-cost production and attractive features, such as flexibility and transparency, for indoor and outdoor applications. In the DSCs, a dye anchored to a semiconductor layer (typically TiO2) is responsible for capturing the sunlight and converting it into electricity. Nevertheless, many commercially available dyes for DSCs are based on a very rare metal, ruthenium, and its replacement with a cheaper, more abundant metal is desirable. A good alternative to ruthenium could be copper, which possesses similar photophysical properties in coordination with diimine ligands, but it is considerably cheaper and relatively earth-abundant. In this work, a particular “on-surface self-assembly” strategy was employed to form, on the surface of TiO2, heteroleptic copper (I) complexes with a “push-pull” design which facilitates the electron transfer from the copper (I) complex into the conduction band of TiO2 and enhances the performance of the photovoltaic devices.This thesis focuses on the investigation of the properties of five new heteroleptic copper (I) complexes bearing the same anchoring ligand but different ancillary ligands. Because of the method employed for their synthesis, a solid-state characterization of the optical and electrochemical properties on TiO2 was performed employing tools such as UV-Vis spectroscopy, cyclic voltammetry (CV), and differential pulse voltammetry (DPV). As internal benchmark through the entire characterization, the homoleptic copper (I) complex with the anchoring ligand was also studied. Some patterns between the heteroleptic complexes on TiO2 and their respective homoleptic complexes in solution were found, opening the possibility to predict the behaviour of unknown heteroleptic complexes starting from their corresponding homoleptic. Furthermore, the characterization was necessary to ensure that the complexes were fulfilling the requirements to be employed as dyes. The performances of the heteroleptic, and of the anchoring-ligand homoleptic, copper (I) complexes were then investigated as photosensitizers in DSC devices mainly by measuring the current density-voltage (J-V) characteristics at different light intensities and in the dark, the incident photon-to-current efficiency (IPCE), and electron lifetimes. As benchmark for the degree of effectiveness of the device, the state-of-the-art ruthenium (II) complex N719 was also studied. All the copper (I) complexes showed an overall similar behaviour. The J-V characteristics showed a power conversion efficiency up to 2,05% for the best performing device, which is 25% of the efficiency of DSCs based on N719. On the other hand, the least performing heteroleptic copper (I) complex studied showed an efficiency of 1,23%. From a general analysis combining all the results obtained, it may be concluded that a reason for the limited photocurrent measured through these devices can be due to incomplete dye coverage of TiO2. Despite the lower performance compared to the standard dye N719, the simplicity of the system is promising, and its considerable economic advantage could pave the way to the use of DSCs in everyday life applications. / Modernt samhälle är mycket beroende på energi och det blir allt mer akut att hitta alternativa källor till fossila bränslen. Solen är den mest riklig energikällan som finns och att utnyttja den effektivt skulle resultera i stora miljö- och ekonomiska genombrott. Färgämne sensibiliserade solceller (”dye-sensitized solar cells”; DSC) utvecklade i 90-talet för sin breda kommersiella potential som härrör från en kombination av låg kostnadsproduktion och attraktiva egenskaper, såsom möjligheter för flexibilitet och transparens. I DSC är ett färgämne förankrat till den ytan av en halvledare (vanligtvis TiO2). Färgämnet är ansvarigt för att fånga solljuset och överföra elektronerna till halvledaren för att producera el. Många kommersiella färgämnen för DSC är baserade på rutenium, en mycket sällsynt metall. Ersättning av rutenium med en billigare, rikligmetall är önskvärt mot mer hållbara DSC. En bra alternativmetall till rutenium är koppar. Komplexen av koppar(I) har liknande fotofysiska egenskaper till rutenium (II) men koppar är mer vanlig och mindre dyr än rutenium. Heteroleptiska koppar(I) komplexen med en "push-pull" design syntetiserades på ytan av TiO2 genom "ytan assisterade självmontering". "Push-pull" designen underlättar elektronöverföring från koppar(I)-komplexet till ledningsbandet av TiO2. Denna avhandling fokuseras på undersökning av egenskaperna av fem nya heteroleptiska koppar(I) komplex med den samma förankrings ligand men olika distala ligander. På grund av metoden som används i syntesen av heteroleptiska koppar(I) komplex, var karakterisering av komplexen vid optiska och elektrokemiska metoder utfördes på TiO2. Metoderna för karakterisering var UV-Vis-spektroskopi, cyklisk voltametri (CV) och differentialpuls voltametri (DPV). Som en intern standard genom hela karaktäriseringen studerades även homoleptiska koppar(I) komplex med förankringsliganden. Egenskaperna på heteroleptiska koppar(I) komplexen på TiO2 ytan kunde förutsägas från mätning av egenskaperna på homoleptiska koppar(I) komplexen. Koppar(I) komplexen är undersöktes som fotosensibiliserare i färg-sensibiliserade solceller. Effektiviteten av solcellerna med koppar(I) komplexen eller rutenium (II) komplex (N719) utvärderades genom att mäta fotokurrentdensitetsspänningen (J-V) vid olika ljusintensiteter, incidentfoton-till-ström effektiviteten (”incident photon-to-current efficiency”; IPCE) och laddningsrekombinationen (elektronlivstiden). Koppar(I) komplexen hade övergripande liknande egenskaper i solceller. En kraft omvandlingseffektivitet av 2,05% nås för den bästa solcellen med ett koppar(I) komplex. Medan den bästa effektiviteten med N719 färgämnet var 7,57%. En svaghet i självmonteringen av koppar(I) komplexen på ytan av TiO2 är den ofullständiga bindningen till ytan men självmonteringen metoden var enkel och kunde skapa många, olika färgämnen i kort tid. Trots den lägre prestandan jämfört med standardfärgen N719 är systemets enkelhet lovande, och dess stora ekonomiska fördel kan bana vägen till användningen av DSC i vardagsläget. / La civiltà moderna è fondata sull’uso dell’energia e trovare fonti alternative ai combustibili fossili è diventato sempre più necessario. La radiazione proveniente dal sole è la risorsa energetica più abbondante e disponibile sul nostro pianeta e sfruttarla al massimo comporterebbe una svolta decisiva per l’ambiente e l’economia. Tra i dispositivi fotovoltaici, le celle di Grätzel, conosciute anche come DSC dall’acronimo inglese (dye-sensitized solar cell), sono emerse per il loro enorme potenziale commerciale, dovuto alla combinazione tra basso costo di produzione e interessanti caratteristiche, come la loro flessibilità e trasparenza, che gli conferiscono la possibilità di integrazione negli edifici e l’uso in applicazioni “indoor”. Nelle DSC, un foto-sensibilizzatore, detto anche dye, ancorato ad uno strato di un materiale semiconduttore (tipicamente TiO2), è responsabile della cattura della luce solare e della sua conversione in elettricità. Tra i dye commercialmente disponibili per le DSC vi sono per lo più complessi di coordinazione basati su un metallo molto raro, il rutenio; la sua sostituzione con un metallo più abbondante ed economico è auspicabile per la diffusione di questa tecnologia. Una buona alternativa al rutenio potrebbe essere fornita dal rame, che possiede proprietà foto-fisiche molto simili al primo quando in coordinazione con diimmine; in più è abbastanza economico e relativamente abbondante sulla Terra. Una particolare strategia di "autoassemblaggio sulla superficie" è stata impiegata per formare, sullo strato di TiO2, complessi eterolettici di rame (I) con un design “push-pull” che facilita il trasferimento di elettroni dal complesso di rame (I) alla banda di conduzione di TiO2, migliorando così le prestazioni dei dispositivi fotovoltaici. Questa tesi si concentra sullo studio delle proprietà di cinque nuovi complessi eterolettici di rame (I) che possiedono lo stesso legante di ancoraggio ma diverso legante secondario. A causa del metodo impiegato per la loro sintesi, è stato necessario eseguire la caratterizzazione delle loro proprietà ottiche ed elettrochimiche direttamente sulla superficie del TiO2, utilizzando strumenti come la spettroscopia UV-Visibile, la voltammetria ciclica (CV) e la voltammetria ad impulsi differenziali (DPV). Come riferimento interno durante l'intera caratterizzazione, è stato studiato anche il complesso di rame (I) omolettico con il legante di ancoraggio. Tra i complessi eterolettici su TiO2 e i loro rispettivi complessi omolettici in soluzione, è stato individuato un trend con la possibilità di prevedere il comportamento dei primi a partire dal loro corrispondente omolettico. Inoltre, la caratterizzazione ottica ed elettrochimica è necessaria per garantire l’adeguatezza dei complessi come dye. Le prestazioni dei complessi eterolettici e del complesso omolettico con il legante di ancoraggio, sono state quindi studiate come foto-sensibilizzatori nei dispositivi DSC; in particolare è stata misurata la curva di densità di corrente – voltaggio (J-V) a diverse intensità di luce e al buio, l’efficienza quantica esterna (EQE o dall’acronimo inglese incident photon-to-current efficiency, IPCE) e infine il tempo di vita dell’elettrone nella banda di conduzione del semiconduttore. Come standard interno, per verificare l’efficacia del dispositivo, è stato anche studiato il ben noto complesso di rutenio (II), N719. Generalmente, tutti i complessi di rame (I) hanno mostrato un comportamento simile. Le curve caratteristiche J-V hanno presentato un'efficienza pari fino al 2,05% per il complesso di rame che ha dato le prestazioni migliori (25% dell'efficienza di N719). Da un'analisi generale che combina tutti i risultati ottenuti, si può concludere che una ragione per cui la foto-corrente risulta limitata potrebbe essere data dall’incompleta copertura del TiO2 da parte del complesso di rame (I) e quindi dallo scarso adsorbimento del dye. Nonostante le prestazioni inferiori rispetto allo standard N719, la semplicità del sistema è promettente e il suo notevole vantaggio economico potrebbe aprire la strada all'utilizzo delle DSC nelle applicazioni della vita quotidiana.

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