Submitted by Maike Costa (maiksebas@gmail.com) on 2016-05-13T14:09:47Z No. of bitstreams: 1 arquivo total.pdf: 4037386 bytes, checksum: 2733330d803024eb0abfbac341b0b0da (MD5) / Made available in DSpace on 2016-05-13T14:09:47Z (GMT). No. of bitstreams: 1 arquivo total.pdf: 4037386 bytes, checksum: 2733330d803024eb0abfbac341b0b0da (MD5) Previous issue date: 2014-08-22 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - CAPES / In the present work, it has been investigated the influence of the position of electron-donor substituents in aromatic carboxylate ligands on the photoluminescent properties of Tb3+ and Eu3+complexes. It was synthesized complexes of general formula [Ln (R-2-Bz)3fen] and [Ln (4-R-Bz)3fen] with Ln = Eu3+, Gd3+ and Tb3+; R =-NH2,-NH (CO) CH3,-OH,-O (CO) CH3,-O (C4H9); phen = 1,10-phenanthroline, which were characterized by complexometric titration, elemental analysis, absorption IR spectra and diffuse reflectance. The phosphorescence spectra of the complexes [Gd (2-R-Bz)3fen] and [Gd (4-R-Bz)3fen] showed that the energies of the triplet states of the ligands are coordinated above and in a good resonance condition with the emitting states of both ions Eu3+ and Tb3+ and it is favorable to the efficient process of ligand-metal energy transfer. Such states are localized on the 1,10-phenanthroline ligands in all complexes. For the complexes of the Tb3+ ion, it was found that acetylation of both substituents N or O-donors caused an increase in the lifetimes for most compounds, which is much higher at ambient temperature than at low temperature. For the Eu3+ complex it was observed a strong dependence of the intensity parameters Ω2 and quantum efficiency of luminescence with the nature and position of the electron-donors substituents, which could be rationalized on the basis of electronic and steric effects. Such effects exerted strong influence on the LMCT charge transfer states, directly contributing to the dependence of the quantum efficiency of luminescence with the position of the electron-donor substituents the carboxylate ligands. Steric interactions promoted conjugation breakage due to the removal of the aromatic ring from the conjugation plane of the carboxylate group, reducing the ability of the electron-donating oxygen atoms and consequently increasing the LMCT energy states. It was demonstrated, for the first time, that the loss of conjugation by steric interaction may eliminate or reduce the effect of LMCT states as a suppression channel of luminescence in Eu3+ complexes. / No presente trabalho, investigou-se a influência da posição de substituintes elétron-doadores em ligantes carboxilatos aromáticos sobre as propriedades fotoluminescentes de complexos dos íons Tb3+ e Eu3+. Foram sintetizados complexos de fórmula geral [Ln(2-R-Bz)3fen] e [Ln(4-R-Bz)3fen] , com Ln = Eu3+, Gd3+ e Tb3+; R = -NH2, -NH(CO)CH3, -OH, -O(CO)CH3, -O(C4H9); fen = 1,10-fenantrolina, que foram caracterizados por titulação complexométrica, análise elementar, espectroscopia de absorção na região do infravermelho e de reflectância difusa. Os espectros de fosforescência dos complexos [Gd(2-R-Bz)3fen] e [Gd(4-R-Bz)3fen] revelaram que as energias dos estados tripleto dos ligantes coordenados encontram-se acima e em boa condição de ressonância com os estados emissores de ambos os íons Eu3+ e Tb3+, o que favorece o processo eficiente de transferência de energia ligante-metal, sendo tais estados localizados sobre os ligantes 1,10-fenantrolina em todos os complexos. Para os complexos do íon Tb3+, observou-se que a acetilação de ambos os substituintes N ou O-doadores causou elevação dos tempos de vida para a maioria dos compostos, sendo bem maiores a temperatura ambiente que a baixa temperatura. Para os complexos do íon Eu3+ observou-se uma forte dependência dos parâmetros de intensidade Ω2 e da eficiência quântica de luminescência com a natureza e a posição dos substituintes elétron-doadores, que puderam ser racionalizados a partir dos efeitos eletrônicos e estéricos, atuando de forma antagônica. Tais efeitos, exerceram forte influência sobre os estados de transferência de carga LMCT, contribuindo diretamente para a dependência da eficiência quântica de luminescência com a posição dos substituintes elétron-doadores dos ligantes carboxilatos. Interações estéricas promoveram a quebra de conjugação devido à retirada do anel aromático do plano de conjugação do grupo carboxilato, reduzindo a capacidade elétron-doadora dos oxigênios e, consequentemente, elevando a energia dos estados LMCT. Foi demonstrado, pela primeira vez, que a quebra de conjugação mediante interação estérica pode eliminar ou reduzir o efeito dos estados LMCT como um canal de supressão da luminescência em complexos do íon Eu3+.

Neste trabalho, o corante 9-aminoacridina foi derivatizado com compostos vinílicos que possuem grupos retiradores de elétrons. A incorporação destes leva à mudanças nas propriedades fotofísicas dos derivados, tais como deslocamentos para regiões de menor energia nos espectros de absorção e emissão, sugerindo a presença de transferência de carga intramolecular (ICT). Os estudos de fluorescência resolvida no tempo confirmam este processo para os derivados. Este estado ICT possui um tempo formação na faixa de 150 – 300 ps e um tempo de vida entre 1 – 3 ns, que depende do solvente. Os derivados que apresentam pelo menos um grupo carbonila como retirador de elétron, possuem um tempo de vida longo na faixa de 8 –10 ns, atribuído à emissão do enol, formado a partir da conjugação estendida por ponte de hidrogênio. A polimerização destes derivados com o ácido metacrílico promoveram mudanças em suas propriedades fotofísicas estacionárias e resolvidas no tempo devido à quebra da conjugação  estendida. Este fato é ilustrado pelos espectros de absorção e emissão que mostram bandas estruturadas, deslocadas para a região de maior energia e um decaimento monoexponencial, semelhante ao observado com 9-aminoacridina. Anisotropia de fluorescência resolvida no tempo mostra que nos copolímeros o tempo de relaxação rotacional do corante é muito sensível à mudança conformacional do poli (ácido metacrílico) com o pH, possibilitando assim o estudo da dinâmica deste polímero em solução aquosa. / In this work, the dye 9-aminoacridine was derivatized with vinylic compounds containing electron withdrawing groups. The incorporation of these groups leads to changes in the photophysical properties of the dye, such a red shift in the absorption and emission spectra, suggesting the presence of intramolecular charge transfer (ICT) effect. Time-resolved studies have confirmed such process in all derivatives. This ICT state has a risetime in the range 150 – 300 ps and a fluorescence lifetime between 1 – 3 ns, that depends of the solvent. The derivatives with at least one carbonyl group as electron withdrawing, have an additional lifetime in the range of 8 –10 ns, attributed to the enol emission formed by the extended conjugation. The polimerization of these derivatives with methacrylic acid induces changes in the stationary and time-resolved properties of the dye due to the breaking of the extended conjugation. This fact is illustrated by the absorption and emission spectra that show structured bands with a blue shift, and a monoexponencial decay, similar to the behavior of 9- aminoacridine. Time-resolved fluorescence anisotropy of the bound dye shows that the copolymers have a segment relaxation of the chain is very sensitive to the change in the conformational shape of poly (methacrylic acid) with pH, and such a process is well indicated by following the rotational relaxation of the dye.

La recherche présentée dans cette thèse traite de la synthèse, propriétés et applications optoélectroniques de matériaux nanohybrides basés sur le greffage d’une porphyrine donneur d’électron et d’un dérivé du fullerène sur des nanoparticules de ZnO.Ces molécules sont accrochées à la surface de l’oxyde métallique grâce à une fonction acide carboxylique. L'effet du rapport molaire porphyrine / fullerène, de la polarité du solvant et la forme des nanoparticules sur les propriétés optiques des nanohybrides ont été étudiés. Les interactions porphyrine / fullerène à l’échelle moléculaire apparaissent pour un rapport de 1:2 à l'état co-greffé sur des nanobâtonnets de ZnO. Cela est indiqué par le fort décalage bathochrome du pic de Soret des porphyrines et de l’extinction de sonémission de fluorescence. Toutefois, à cette valeur du rapport, le complexe de transfert de charge n'est pas détectable. La formation de ce complexe requiert à la fois les molécules donneur et accepteur d’électron d'être d’être maintenues à proximité, ce qui est réalisableen augmentant le rapport stoechiométrique à 1:3 et au-delà. Dans l’acétonitrile, une bande d’absorption de transfert de charge de faible intensité apparaît vers 700-800 nm, ainsi qu’une bande d'émission à 800 nm, caractérisant la complexation supramoléculaire à la surface de l’oxyde métallique. Lorsqu'ils sont utilisés pour la fabrication de la couche active dans une cellule solaire à hétérojonction hybride, les nanobâtonnets de ZnO fonctionnalisés montrent une efficacité de conversion lumineuse pour des valeurs faibles du rapport porphyrine / fullerène, mais l’augmentation du taux de fullerène tend à diminuer le rendement de conversion photovoltaïque. Cet effet a été relié à l’apparition de défauts morphologiques dans les films minces induite par l’agrégation des nanotubeslié au taux et rapport de greffage des molécules organiques. / The research presented in this dissertation deals with the synthesis, properties andoptoelectronic applications of the nanohybrids based on dye and fullerene functionalizedZnO nanoparticles. These molecules being acid functionalized, were co-grafted on thesurface of ZnO nanoparticles. The effect of changing ratio of donor to acceptor, polarityof the solvent and shapes of the nanoparticles on porphyrin/fullerene interaction werestudied. The molecules were found appreciably interacting at a ratio of 1:2 under the cograftedstate on ZnO nanorods. This was indicated by the strong bathochromic shift of thesoret peak of porphyrin and quenching of its fluorescence however, at this ratio chargetransfer complex is not detectable. The complex formation requires both the donors andacceptors to be enough close to each other to undergo Van der Waal’s type interactionwhich is achievable by raising the stoichiometric ratio to 1:3 and beyond. Weak CTabsorption (700-800 nm) and emission bands (800 nm) characterizing supramolecularcomplexation, were noticed only in polar solvent acetonitrile. When applied as acomponent of the active layer in bulk heterojunction hybrid solar cells, the dyefunctionalized ZnO nanoprods raised the efficiency of the solar cells at lowconcentrations but addition of fullerene had an inverse effect. This was investigated to bedue to the morphological defects induced by the clusterization of nanorods.

Doctorat en Sciences / info:eu-repo/semantics/nonPublished

A series of 28 square-planar dithiol(diimine)platinum(II) chromophoric complexes have been synthesized, characterized, and evaluated for potential efficacy in sensitization of solid state photovoltaic devices to the near-infrared regions of the electromagnetic spectrum. The effect of molecular stacking in the solid state and self-association in solution are shown to influence spectral, electronic, and magnetic properties of the chromophores. Such properties are investigated in the pure form and as partners in donor-acceptor charge transfer adducts. Finally, selected chromophores have been incorporated into single layer schottky diodes as neat films and as dopants in multi-layer organic photovoltaic devices. Evaluation of the devices internal quantum efficiency and voltage-current was measured as proof of concept.

Harnessing the Sun’s energy via the conversion of solar photons to electricity has emerged as a sustainable energy source to fulfill our future demands. In this regard, solution-processable, size-tunable PbS quantum dots (QDs) have been identified as a promising active materials for photovoltaics (PVs). Yet, there are still serious challenges that hinder the full exploitation of QD materials in PVs. This dissertation addresses two main challenges to aid these QDs in fulfilling their tremendous potential in PV applications. First, it is essential to establish a large-scale synthetic technique which maintains control over the reaction parameters to yield QDs with well-defined shape, size, and composition. Rigorous protocols for cost-effective production on a scale are still missing from literature. Particularly, previous reports of record-performance QD-PVs have been based on small-scale, manual, batch syntheses. One way to achieve a controlled large-scale synthesis is by reducing the reaction volume to ensure uniformity. Accordingly, we design a droplet-based continuous-flow synthesis of PbS QDs. Only upon separating the nucleation and growth phases, via a dual-temperature-stage reactor, it was possible to achieve high-quality QDs with high photoluminescence quantum yield (50%) in large-scale. The performance of these QDs in a PV device was comparable to batch-synthesized QDs, thus providing a promise in utilizing automated synthesis of QDs for PV applications. Second, it is crucial to study and control the charge transfer (CT) dynamics at QD interfaces in order to optimize their PV performance. Yet, the CT investigations based on PbS QDs are limited in literature. Here, we investigate the CT and charge separation (CS) at size-tunable PbS QDs and organic acceptor interfaces using a combination of femtosecond broadband transient spectroscopic techniques and steady-state measurements. The results reveal that the energy band alignment, tuned by the quantum confinement, is a key element for efficient CT and CS processes. Additionally, the presence of interfacial electrostatic interaction between the QDs and the acceptors facilitates CT from large PbS QD (bandgap < 1 eV); thus enabling light-harvesting from the broad near-infrared solar spectrum range. The advances in this work – from automated synthesis to charge transfer studies – pave new pathways towards energy harvesting from solution-processed nanomaterials.

The performance of non-fullerene acceptor (NFA)- based organic solar cells (OSC) has shown continuous increase in recent years, reaching power-conversion efficiencies up to 17% through the design and synthesis of efficient acceptor materials. Recent research is directed towards achieving higher efficiency of OSC, which is limited by the open-circuit voltage (Voc) which is lower than the Voc values achieved in inorganic or perovskites solar cells with comparable bandgaps. In this work, voltage losses in NFA based OSC were calculated by investigating charge-transfer state energy (ECT) using electroluminescence spectroscopy and sensitive external quantum efficiency in three polymer:non-fullerene bulk heterojunction solar cells. PCE10:ITIC device acquired the highest ECT with a Voc of 0.82V, and a a power conversion efficiency (PCE) of 7.91%. While PCE10:O-IDTBR obtained the highest Voc of 1.03V, a PCE of 8.02% compared to PCE10:O-IDTBCN solar cell that has a lower Voc of 0.73V with a PCE of 7.98%. Both radiative and non-radiative voltage losses were calculated. In this thesis, the high open circuit voltage of PCE10:O-IDTBR is explained by the low non-radiative voltage losses compared to PCE10:O-IDTBCN and PCE10:ITIC devices.

The efficiency of photoconversion systems, such as organic photovoltaic (OPV) cells, is largely controlled by a series of fundamental photophysical processes occurring at the interface before carrier collection. A profound understanding of ultrafast interfacial charge transfer (CT), charge separation (CS), and charge recombination (CR) is the key determinant to improving the overall performances of photovoltaic devices. The discussion in this dissertation primarily focuses on the relevant parameters that are involved in photon absorption, exciton separation, carrier transport, carrier recombination and carrier collection in organic photovoltaic devices. A combination of steady-state and femtosecond broadband transient spectroscopies was used to investigate the photoinduced charge carrier dynamics in various donor-acceptor systems. Furthermore, this study was extended to investigate some important factors that influence charge transfer in donor-acceptor systems, such as the morphology, energy band alignment, electronic properties and chemical structure. Interestingly, clear correlations among the steady-state measurements, time-resolved spectroscopy results, grain alignment of the electron transporting layer (ETL), carrier mobility, and device performance are found. In this thesis, we explored the significant impacts of ultrafast charge separation and charge recombination at donor/acceptor (D/A) interfaces on the performance of a conjugated polymer PTB7-Th device with three fullerene acceptors: PC71BM, PC61BM and IC60BA. Time-resolved laser spectroscopy and high-resolution electron microscopy can illustrate the basis for fabricating solar cell devices with improved performances. In addition, we studied the effects of the incorporation of heavy metals into π-conjugated chromophores on electron transfer by monitoring the triplet state lifetime of the oligomer using transient absorption spectroscopy, as understanding the mechanisms controlling intersystem crossing and photoinduced electron transfer dynamics is required to improve the device performance of solar cells. Here, we evaluated the effects of incorporating Pt(II) on intersystem crossing and photoinduced electron transfer by comparing and analyzing the photoexcited dynamics of DPP-Pt(II)(acac) and metal-free DPP with different acceptors such as TCNE, TMPyP, and TPyP.

Organic materials such as phthalocyanine-based systems present a great potential for organic device applications due to the possibility of integrating films of different organic materials to create organic heterostructures which combine the electrical capabilities of each material. This opens the possibility to precisely engineer and tune new electrical properties. In particular, similar transition metal phthalocyanines demonstrate hybridization and charge transfer properties which could lead to interesting physical phenomena. Although, when considering device dimensions, a better understanding and control of the tuning of the transport properties still remain in the focus of research. Here, by employing conductive atomic force microscopy techniques, we provide an insight about the nanoscale electrical properties and transport mechanisms of MnPc and fluorinated phthalocyanines such as F16CuPc and F16CoPc. We report a transition from typical diode-like transport mechanisms for pure MnPc thin films to space-charge-limited current transport regime (SCLC) for Pc-based heterostructures. The controlled addition of fluorinated phthalocyanine also provides highly uniform and symmetric-polarized transport characteristics with conductance enhancements up to two orders of magnitude depending on the polarization. We present a method to spatially map the mobility of the MnPc/F16CuPc structures with a nanoscale resolution and provide theoretical calculations to support our experimental findings. This well-controlled nanoscale tuning of the electrical properties for metal transition phthalocyanine junctions stands as key step for future phthalocyanine-based electronic devices, where the low dimension charge transfer, mediated by transition metal atoms could be intrinsically linked to a transfer of magnetic moment or spin. / Dieser Beitrag ist aufgrund einer (DFG-geförderten) Allianz- bzw. Nationallizenz frei zugänglich.

Abstract: Understanding and controlling the ultrafast charge carrier and exciton dynamics at the interface of semiconductor nanocrystals (NCs) offer an excellent opportunity to improve the charge collection and the overall performance of many optoelectronic and energy-based devices. In this dissertation, we study how interfacial engineering of these materials can have a direct influence on controlling the charge transfer and the nonradiative losses in different donor-acceptor systems. The first introductory chapter provides an overview of all the fundamental photophysical processes controlling the interfacial phenomena. Then, the second chapter highlights all the chemicals and synthesis methods employed during this thesis. The subsequent two chapters discuss the detailed experimental studies and observations related to different materials and interfaces. First, it describes how we can dramatically tune the intersystem crossing (ISC) rate, the triplet state lifetime, turn on/off the electron injection at the CdTe-Prophyrin interface via tuning either the quantum dot size or the porphyrin molecular structure. Also, how the intermolecular distances, electronic coupling, and subsequently, the photoinduced charge transfer can be controlled by the interfacial electrostatic interactions at CdTe-Fullerene interfaces. Second, due to the promise that of perovskite NCs holds for improving many solar cell and optoelectronic applications, chapter 3 highlights the tremendous effect that the shape of perovskite nanocrystals has on the rate and the mechanism of charge transfer at the MAPbBr3- TCNE interface. Besides, it demonstrates how the confinement effect brought by changing the dimensionality influence the charge transfer dynamics at the MAPbBr3-BQ interface. Finally, it explains how the effective passivation of the surface defects and the subsequent suppression of the formation of surface nonradiative recombination centers in CsPbCl3 NCs controls the photoluminescence quantum yield and the photodetector performance.