The depletion of fossil fuels and the increasing energy demand for energy has led to the search for better and improved technologies with special focus renewable energy, especially solar cells. The first generation solar cells based on silicon are expensive, hence dye sensitized solar cells come in as a better alternative as these solar cells are environmental friendly, they have moderately good conversion efficiency and they are relatively cheap to produce. Dithiocarbamate ligands have been widely used in many research fields, as these are versatile ligands. Coordination of dithiocarbamates with metals such as ruthenium has produced high conversion efficiency and have the ability to extend the MLCT absorptions, and this can further extend their wavelength. In this study five dithiocarbamate sodium salt ligands were prepared and were coded as FL1= Aniline, FL2= p- toluidine, FL3= p- anisidine, FL4=dibenzyl, FL5=diphenyl. These ligands were used to synthesize Ru(II) metal complexes which were formulated as [Ru(FLx)(dcbpy)(NCS)] and [Ru(FLx)2(dcbpy)] where FLx is the dithiocarbamate ligand and dcbpy is 2,2-bipyridine-4,4’-dicarboxylic acid and the complexes were coded as FCx. The synthesized compounds were characterized using techniques such as the melting point, molar conductivity, FT-IR and NMR spectroscopy. For spectroelectrochemical studies of the metal complexes, techniques such as UV-Vis and photoluminescence spectroscopy were carried out. Furthermore, redox properties of the complexes were analyzed using cyclic and square wave voltammetry. The FT-IR displayed all the expected peaks of interest both in the dithiocarbamate ligands and in the metal complexes. The electronic spectra confirmed the successful coordination of ligand to the metal centre, the electronic spectra of the complexes also confirmed the six coordinate octahedral geometry of the complexes. The complexes exhibited some photoluminescence properties that are suitable for dye sensitization. The cyclic voltammogram of the complexes displayed more reduction potentials that could be attributed to the π-conjugation in the ligands incorporated during synthesis. The square wave voltammogram of the complexes is in agreement with the results obtained in cyclic voltammetry.

Organic photovoltaic (OPV) is an exciting energy harvesting technique. Although its power conversion efficiency (PCE) now exceeds 10% in a research laboratory, the processing window of an OPV cell is still narrow. A fundamental understanding of the OPV materials is desired. This thesis presents the charge carrier transport properties and electronic interactions in the bulk heterojunction (BHJ) active layer of OPV cells. They were found to be well correlated with OPV device performances. Space-charge-limited current (SCLC) measurements and admittance spectroscopy (AS) were employed to study the charge transports, while photothermal deflection spectroscopy (PDS) was used to probe the trap densities inside the materials. Beneficial effects of a common solvent additive, 1,8-diiodooctance (DIO), on PTB7:PC71BM OPV cells have been investigated. With DIO present in the casting solution, the resulting BHJ films have much enhanced electron mobilities, whereas the impact on the hole mobility is negligible. The origin of increased electron mobility is the reduced average electron hopping distance for those films prepared with DIO solvent additive. A balance of hole-electron mobility by tuning the DIO concentration was demonstrated to be the way to optimize the OPV device performance. In light of carrier transport measurement results, a "polymer-rich" strategy with preserved device performance was demonstrated. After understanding the importance of balanced hole-electron mobility, the impact of donor-acceptor weight ratio on the performance of PTB7 : PC71BM based OPV cells was explored. Early stage electronic donor-acceptor interactions were revealed using ultra-low dosages of fullerenes. Before electron transport pathways percolate, the unconnected fullerene domains act as traps and hinder electron transport. From PDS, the trap density observed inside BHJ films was found to be anti-correlated with the fill factor of OPV devices. The origin of low FFs is mainly due to electron traps and localized states from fullerenes. Based on the observations, it is proposed that PC71BM tends to intercalate with PTB7 backbone instead of forming self-aggregates before the electron pathway percolation. Apart from investigating the fundamentals in OPV devices, a solution to improve its processing window was proposed in this thesis. Thermally stable polymer : fullerene OPV cells were fabricated by employing fluorenone-based solid additives. A charge transfer interaction between the additives and donor moiety of polymer formed a locked network which freezes the BHJ morphology under thermal stress. The most promising result retains 90% of the origin efficiency, upon thermal aging at 100 °C for more than 20 hours in PTB7:PC71BM solar cells. Besides fullerene-based OPV, all-polymer photovoltaic solar cells (all-PSCs) were also investigated. Two new difluorobenzene-naphthalene diimide based polymer electron acceptors, one random (P1) and one regioregular (P2) structure, were compared. P2 exhibited a much better molecular packing, a higher electron mobility and more balanced hole-electron mobilities in its composite film with polymer donor, PTB7-Th. An optimized PTB7-Th:P2 device can achieve a respectably high PCE over 5% for all-PSC devices. These all-PSCs should open a new avenue for next generation OPVs.

In thin films solar cells technology, many different materials have been used; however, toxic and expensive materials and techniques have been widely employed up to date. In this work, three different low/non-toxic materials were grown by means simple and cheap techniques.Cd1–xZnxS thin films with Zn concentrations of 0–5 at.% were analyzed. The effect of the addition of different molar Zn concentrations to the reaction mixture on the growth mechanism of Cd1–xZnxS thin films and the influence of these mechanisms on structural, optical and morphological properties of the films has been studied.Cd1–xZnxS thin films were synthesized by chemical bath deposition using an ammonia-free alkaline solution. Microstructural analysis by X-ray diffraction showed that all deposited films grew with hexagonal wurtzite structure and crystallite sizes decreased as the Zn concentration in the film increased. Optical measurements indicated a high optical transmission between 75 % and 90 % for wavelengths above the absorption edge. Band gap value increased from 2.48 eV to 2.62 eV, and the refractive index values for Cd1–xZnxS thin films decreased as the Zn increased. These changes in films and properties are related to a modification in growth mechanism of the Cd1–xZnxS thin films, with the influence of Zn(OH)2 formation being more important as Zn in solution increased.Characterization of ZnS thin films deposited by chemical bath in a non-toxic alkaline solution is reported. The effect of deposition technique (growth in several times) on the properties of the ZnS thin film was studied. The films exhibited a high percentage of optical transmission (greater than 80 %); as the deposition time increased a decreasing in the band gap values from 3.83 eV to 3.71 eV was observed. From chemical analysis, the presence of ZnS and Zn(OH)2 was identified and X-ray diffraction patterns exhibited a clear peak corresponding to ZnS hexagonal phase (103) plane, which was confirmed by electron diffraction patterns. From morphological studies, compact samples with well-defined particles, low roughness, homogeneous and pinhole-free in the surface were observed.On the other side, characterization of one-step electrodeposited CuInS2 thin films is reported. The effect of the complexing agent C8H5KO4 on the reduction potential of metallic ions, as well as the annealing conditions to avoid film oxidation was studied. From polarization curves, it was observed that C8H5KO4 is an appropriate complexing agent to bring the reduction potential of Cu2+ closer to In3+. XRD patterns showed films with hexagonal structure and no peaks attributed to oxide phases were observed, under a 95 % N2 + 5 % H2 atmosphere and using a carbon holder. However, others two weak peaks associated to Cu7S4 phase were identified. The CuInS2 thin films exhibited a band gap value of 1.50 eV, low optical transmission in the visible range, p-type conductivity and a charge carrier concentration of 2.3 × 10-18 cm-3. Finally, from morphological and chemical analysis, it was possible to observe a compact morphology and free of pinholes surface with a composition close to the stoichiometric one. / Doctorat en Sciences de l'ingénieur et technologie / info:eu-repo/semantics/nonPublished

Easy manufacturing, light weight and inexpensive materials are the key qualities of organic solar cells that makes them a highly researched area. To make organic solar cells adequate for the market, the efficiency of power conversion has to increase further, and the lifetime of organic solar cells has to improve. Avoiding recombination losses is a piece in the puzzle that can make organic solar cells more efficient. Organic solar cells with two different hole transport layers were therefore examined by I-V measurements. It was found that the organic solar cell with MoO3 as the HTL possesses a higher current density in both the reverse region and forward region. The higher current density in both regions points towards a less successful blocking of electrons travelling to the anode (reverse region) and a better ability to transport holes from the active layer to the anode. Insight to different state of recombination was also found from the slope values in the Voc and Jsc as a function of light intensity plots. It was concluded that both solar cells experience a dominant monomolecular recombination under short circuit condition and evolved into bimolecular recombination under open circuit condition. However, the cell with CuSCN showed a more dominant bimolecular recombination, which was shown from a slope closer to one unity kT/q in the Voc as a function of light intensity plot.

Bulk heterojunction organic solar cells (BHJ OSCs) have been recognized as one of the most promising next generation green technology alternatives to inorganic solar cells because of the low-cost, lightweight, flexibility. Specifically, the use of small molecules instead of polymers as donors in BHJ OSC have been developed very fast recently because small molecules can be facilely synthesized and easily purified, and have a determined molecular structure without batch-to-batch variations. To date, those among the most efficient small molecules were constructed as acceptor-donor-acceptor (A-D-A) structural configuration from electron-rich units such as benzodithiophene (BDT), dithienosilole (DTS), oligothiophene units, and electron-deficient units such as benzothiadiazole (BT), diketopyrrolopyrrole (DPP), isoindigo (IID) and perylenediimide (PDI). Surprisingly, porphyrins were rarely studied either in polymers or π-conjugated small molecules as donor materials, though they have unique chemistry together with excellent photochemical and electrochemical properties, such as facile functionalization of the periphery and the variation of the central atom (metal ions), strong UV-visible absorption, ultrafast photoinduced charge separation in porphyrin-fullerene systems. In this research work, we design, synthesize and characterize new porphyrin-based small molecules with acceptor-donor-acceptor (A-D-A) configuration for bulk heterojunction organic solar cells, and investigate their structure-property relationships, specifically the effect of peripheral and backbone alkyl side-chains, π-conjugated linkers as well as electron-deficient ending units on the charge mobility, film morphology and solar cell performances. In Chapter 1, a general review on the historic and recent development of BHJ OSCs was given first, including the major components and working principle of OSC, the versatile organic semiconductors and their performances in OSCs. In chapter 2, six A-D-A structural porphyrin small molecules were designed and synthesized, in which different peripheral alkyl substitutions are attached to the meso-position of porphyrin core (CS-I, CS-II, CS-III, CS-4, CS-5 and CS-6), and 3-ethylrhodanine is used as terminal group. Their UV-visible absorption in solid, energy level, blend film morphology, charge mobility and cell performance are dependent on the different peripheral substitutions. The active layer consists of these six small molecules as donor materials and PC71BM as the acceptor material with an optimized film thickness. Although all six molecules show similar optical spectrum in solutions, the introduction of linear alkyl side chains can promote thin-film nanostructural order, especially shown to shorten π-π stacking distances between backbones and increase the correlation lengths of both π-π stacking and lamellar spacing, leading to higher efficiency in this serial. Among them, the highest power conversion efficiency of 9.09% has been achieved by CS-4 based devices. In chapter 3, another two new A-D-A porphyrin small molecules (PTTR and PTTCNR) have been developed, which are similar in structure to CS-I, II and III, except that the linker is phenylethynyl in CS-I, II and III, whereas it is terthiophenylethynyl in PTTR and PTTCNR. The highest power conversion efficiency of 8.21% is achieved by PTTCNR, corresponding to a JSC of 14.30 mA cm−2, VOC of 0.82 V, and FF of 70.01%. The excellent device performances can be ascribed to the conjugated structure of porphyrin with 3,3''-dihexyl-terthiophene and the aliphatic 2-octylundecyl peripheral substitutions, which not only effectively increase the solar flux coverage between the conventional Soret and Q bands of porphyrin unit, but also optimize molecular packing through polymorphism associated with side-chain and the π-conjugated backbones, and form the blend films with [6,6]-phenyl-C71-butyric acid methyl ester (PC71BM) characteristics of bi-continuous, interpenetrating networks required for efficient charge separation and transportation.;In chapter 4, we designed and synthesized a new dimeric porphyrin donor molecule (CS-DP) containing A-π2-D-π1-D-π2-A architecture by coupling of two zinc porphyrin cores through ethynyl linker. Interestingly, it can harvests the photons up to deep near-infrared (NIR) region in the absorption spectrum. From the past decades, it has been found that developing donor molecules with the absorption spectral in NIR region is a challenging key factor to get the high performance BHJ OSCs. Solar cell devices employing CS-DP as a donor exhibit a highest power conversion efficiency of 8.23%, corresponding to JSC = 15.14 mA cm-2, VOC = 0.781 mV and FF = 69.8% under AM 1.5G solar radiation. The high efficiency of this molecule is attributed to a panchromatic IPCE action spectrum from 300 nm to 1000 nm. Also, this performance is best for the reported deep NIR organic solar cells based on single small molecule and PC71BM system so far. We envision that this new small bandgap dimeric porphyrin is very promising to use in ternary and multi-junction applications as well as NIR photodetectors. In chapter 5, a series of new A-D-A structural porphyrin small molecules (CS-10, CS-11 and CS-12) have been prepared, that contain the same meso-thienyl-thioalkyl substituted porphyrin core and 3-ethylrhodanine ending unit, but varies with different numbers of phenylethynyl linker. Using them as donors for solution-processed organic solar cells, the device based on CS-10 featuring single phenyl ethynyl π-linker exhibits high power conversion efficiency (PCE) of 7.0%. The results indicate that meso-thienyl-thioalkyl substitution and controlled π-linker length is beneficial to tune the optoelectronic properties, film morphology and consequently performance of porphyrin-based BHJ OSCs. In chapter 6, two symmetrical tetra-meso-substituted porphyrin molecules (ZnP and CuP) have been prepared in gram-scale through the direct condensation of pyrrole and 4-[bis(4-methoxyphenyl)amino]benzaldehyde. Its Zn(II) and Cu(II) complexes exhibit excellent thermal and electrochemical stability, specifically, high hole mobility and very favorable energetics for hole extraction that render them attractive for implementation as new hole transporting materials in organometallic halide perovskite solar cells (PSCs). As expected, the use of ZnP as HTM in PSCs affords a competitive PCE of 17.78%, which is comparable to the most powerful HTM of Spiro-OMeTAD (18.59%) under the same working conditions. Meanwhile, the metal centers affect somewhat the photovoltaic performances that CuP as HTM produces a relative lower PCE of 15.36%. Notably, the perovskite solar cells employing ZnP show longer stability than that of Spiro-OMeTAD. Moreover, the two porphyrin-based HTMs can be prepared from relatively cheap raw materials with a facile synthetic route. The results demonstrate that ZnP and CuP can be a new class of HTMs for efficient and stable perovskite solar cells. To the best of our knowledge, this is the highest performance for porphyrin-based perovskite solar cells with PCE > 17%. The dissertation was completed with conclusions and outlooks in chapter 7.

Over the last five years hybrid organic-inorganic metal halide perovskites have attracted strong interest in the solar cell community as a result of their high power conversion efficiency and the solid opportunity to realise a low-cost as well as industry-scalable technology. Nevertheless, several aspects of this novel class of materials still need to be explored and the level of our understanding is rapidly and constantly evolving, from month to month. This dissertation reports investigations of perovskite solar cells with a particular focus on their local chemical composition. The analytical characterisation of such devices is very challenging due to the intrinsic instability of the organic component in the nanostructured compounds building up the cell. STEM-EDX (Scanning Transmission Electron Microscopy - Energy Dispersive X-ray spectroscopy) was employed to resolve at the nanoscale the morphology and the elemental composition of the devices. Firstly, a powerful procedure, involving FIB (Focus Ion Beam) sample preparation, the acquisition of STEM-EDX maps and the application of cutting edge post-processing data techniques based on multivariate analysis was developed and tested. The application of this method has drastically improved the quality of the signal that can be extracted from perovskite thin films before the onset of beam-induced transformations. Morphology, composition and interfaces in devices deposited by using different methodologies and external conditions were then explored in detail by combining multiple complementary advanced characterisation tools. The observed variations in the nanostructure of the cells were related to different photovoltaic performance, providing instructive indications for the synthesis and fabrication routes of the devices. Finally, the main degradation processes that affect perovskite solar cells were probed. STEM-EDX was used in conjunction with the application of in situ heating, leading to the direct observation of elemental species migration within the device, reported here for the first time with nanometric spatial resolution. Further analyses, involving a set of experiments aimed to study the effects of air exposure and light soaking on the cells, were designed and performed, providing evidence of the main pathways leading to the drastic drop in the device performance.

Made available in DSpace on 2014-06-11T19:35:08Z (GMT). No. of bitstreams: 0 Previous issue date: 2008-06-30Bitstream added on 2014-06-13T19:45:03Z : No. of bitstreams: 1 goncalves_as_dr_araiq.pdf: 8384691 bytes, checksum: 99f915f60f4aa419101cf4839adc9f92 (MD5) / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES) / Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP) / Com o objetivo de melhorar o transporte eletrônico no eletrodo nanoestruturado de ZnO, íons Ga3+ foram utilizados neste trabalho como dopantes e/ou modificadores da superfície. Nanopartículas de ZnO e ZnO:Ga 1, 3 e 5% cristalinas foram preparadas pelo método da precipitação a baixa temperatura. Nenhuma evidência da formação de ZnGa2O4, mesmo na amostra ZnO:Ga 5%, foi detectada por DRX. Dados de XPS revelaram que Ga está presente na matriz de ZnO como Ga3+. O tamanho de partícula diminuiu com o aumento na quantidade de gálio, como observado por FE-SEM, provavelmente devido a uma velocidade de hidrólise mais rápida. O menor tamanho de partícula proporcionou filmes com maior porosidade e área superficial, possibilitando uma maior quantidade de corante adsorvida. Quando estes filmes foram aplicados em células solares, o dispositivo baseado em ZnO:Ga 5% apresentou eficiência global na conversão de energia de 6% (a 10 mW cm-2), um valor três vezes maior que o observado para as células solares de ZnO neste trabalho. Este é um dos maiores valores já relatados para células solares de ZnO. Estudos por TAS da dinâmica fotoinduzida em filmes de ZnO:Ga sensibilizados revelaram um maior rendimento do cátion do corante com o aumento na quantidade de gálio, além de uma aceleração no processo de recombinação de carga. Este estudo indica que a dopagem de ZnO com íons Ga3+ possibilita um aumento na fotocorrente e eficiência global do dispositivo. O coeficiente de difusão (D) e o tempo de vida do elétron (τ) foram estudados em células solares seladas por SLIM-PCV. Em comparação às células solares de ZnO, menores valores de D e maiores valores de τ foram observados nas células solares de ZnO:Ga. O mesmo comportamento foi também observado por EIS. Em condições de densidade eletrônica equivalente, os menores valores de Voc em células solares de ZnO:Ga comparados... / In order to enhance the electron transport properties in the ZnO nanostructured electrode, Ga3+ was used in this work as the impurity ions as either surface modifiers and/or dopants. Highly crystalline ZnO and Ga-modified zinc oxide (ZnO:Ga) nanoparticles containing 1, 3, and 5 at.% of Ga3+ were prepared by the precipitation method at low temperature. No evidence of ZnGa2O4, even in the samples containing 5 at.% of Ga3+, was detected by XRD. XPS data revealed that Ga is present into the ZnO matrix as Ga3+. The particle size decreased as the gallium concentration was raised as observed by SEM, which might be related to a faster hydrolysis reaction rate. The smaller particle size provided films with higher porosity and surface area, enabling a higher dye loading. When these films were applied to DSSCs as photoelectrodes, the device based on ZnO:Ga 5 at.% presented an overall conversion efficiency of 6% (at 10 mW cm-2), a three-fold increase compared to the ZnObased DSSCs under the same condition. This is one of the highest efficiencies reported so far for ZnO-based DSSCs. The transient absorption (TAS) study of the photoinduced dynamics of dye-sensitized ZnO:Ga films showed the higher the gallium content, the higher the amount of dye cation formed, while a faster recombination dynamics was observed. The study indicates that Ga-modification of nanocrystalline ZnO leads to an improvement of photocurrent and overall efficiency in the corresponding device. The diffusion coefficient (D) and electron lifetime (τ) were studied in sealed DSSCs by SLIM-PCV. In comparison to the DSSCs based on ZnO electrodes, the ZnO:Ga-based cells provided lower D values and higher values of τ. The result was interpreted with transport limited recombination. The same behavior was also observed by EIS. At matched electron densities, a lower open-circuit voltage (Voc) of DSSCs based on ZnO:Ga was observed... (Complete abstract click electronic access below)

Made available in DSpace on 2014-12-02T11:16:41Z (GMT). No. of bitstreams: 0 Previous issue date: 2014-02-14Bitstream added on 2014-12-02T11:21:00Z : No. of bitstreams: 1 000752686.pdf: 1677927 bytes, checksum: 39259b0bc7b91b06d1866f18b7b5f124 (MD5) / Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq) / Atualmente existe uma grande demanda no desenvolvimento de novas fontes de energia. Uma das possíveis alternativas para produção de energia são as células solares e, dentre estas, as células solares orgânicas. Estas ainda apresentam baixa eficiência na conversão de energia, por isso um grande número de pesquisas vem sendo realizadas com o intuito de melhorar suas características. No presente trabalho estudamos os componentes aceitadores de elétrons, utilizados na camada ativa das células solares orgânicas, especificamente aqueles formados por C60 e seu derivados, que têm sido amplamente estudados, devido ao seu bom desempenho. Estes estudos visam principalmente ajustar os níveis eletrônicos, assim possibilitando o aumento da tensão de circuito aberto e, por sua vez, aumentando a eficiência de conversão de energia. Nesse trabalho propõe-se uma metodologia que apresenta bons resultados na representação das propriedades estruturais e eletrônicas dos sistemas aqui estudados. Esta metodologia utiliza níveis de teoria semi-empíricos e ab initio. Também foram investigados métodos para correlacionar as propriedades eletrônicas dos materiais estudados com a tensão de circuito aberto, já que esta tensão está diretamente relacionada à eficiência das células solares orgânicas. Através deste trabalho encontramos um método capaz de simular a tensão de circuito aberto com desvio médio de 13%. Por fim, investigamos possíveis substituições químicas em derivados de C60. A partir desse estudo, notamos padrões de comportamentos nos níveis eletrônicos ocasionados de acordo com o tipo de substituinte / Today, there is a great demand in the development of new energy resources. One of the possible alternatives for energy production are solar cells and, among them, organic solar cells. They still have low efficiency in energy conversion, therefore a lot of research has been conducted in order to improve their characteristics. In this work we studied the electron acceptor components, used in the active layer of organic solar cells, specifically those formed by C60 and its derivatives, which have been widely studied because their good charge transport properties. These studies mainly aim at adjusting the electronic levels, thus enabling the increase of the open circuit voltage and increasing the efficiency of energy conversion. In this work we propose a methodology that provides good results in the representation of the structural and electronic properties of the systems hereby studied. This methodology is a mix of semiempirical and ab initio theory levels. We also investigated methods to correlate the electronic properties of materials studied with the open circuit voltage, as this is directly linked to the efficiency of organic solar cells. Through this work we found a method to simulate the open-circuit voltage with a medium deviation of 13%. And finally, we investigate possible chemical substitutions on the C60 derivatives. From this study, we observed patterns in electron levels behavior caused according to the type of the substituent

Organic solar cells (OSCs) have attracted significant attention due to their potential of large area solution fabrication capability at low-cost. For bulk heterojunction (BHJ) OSCs, a thin film of transparent conducting indium tin oxide (ITO), coated on glass or flexible plastic substrate, is widely used as a front electrode. However, indium is not abundant on Earth. Its price has increased continuously over the past 10 years and will likely become an obstacle for the commercialization of OSCs at low cost. Aluminum-doped zinc oxide (AZO) is a promising ITO alternative due to its advantages of high electric conductivity, optical transparency, non-toxicity and low cost. However, reports on OSCs using AZO electrode are quite limited, due to the relatively lower power conversion efficiency (PCE) of AZO-based OCSs as compared to that of ITO-based OCSs. This work focused on studies of high performance AZO-based OSCs through AZO surface modification, absorption enhancement and process optimization. The optical and electronic properties of AZO film including transmittance, sheet resistance, surface morphology and surface work function were characterized. AZO-based OSCs with conventional and inverted structures were fabricated. It was found that AZO-based OSCs with inverted structure demonstrated superior performance than the ones with conventional structure. The inverted structure avoids the use of acidic PEDOT:PSS hole transporting layer, allows the improving of the absorbance of the OSCs and therefore its efficiency. An AZO front transparent cathode was used for application in high performance inverted BHJ OSCs. The photoactive layer consisted a blend of poly[[4,8-bis[(2- ethylhexyl)oxy] benzo [1,2-b:4,5-b'] dithiophene-2,6- diyl][3-fluoro- 2-[(2-ethylhexyl) carbonyl]thieno[3,4-b]thiophenediyl]](PTB7):3'H-Cyclopropa[8,25][5,6]fullerene- C70- D5h(6)-3'-butanoicacid, 3'-phenyl-, methyl ester (PC70BM). A structurally identical control OSC having an ITO front cathode was also fabricated for comparison studies. The structure of OSCs was optimized to achieving absorption enhancement in the active layer. AZO and ITO were modified with a 10 nm thick solution-processed ZnO interlayer to facilitate the efficient electron extraction. The results revealed that bilayer AZO/ZnO and the ITO/ZnO cathodes possess similar electron extraction property. AZO layer has a transparency cutoff at wavelength < 380 nm, results in a slight decrease in the short-circuit current density (JSC). However, the decrease in JSC is very small because the main energy of solar irradiation falls in the spectrum with wavelength > 380 nm. It shows that AZO-based OSCs have a promising PCE of 6.15%, which is slightly lower than that of a control ITO-based OSC (6.57%). AZO-based OSCs, however, demonstrate an obvious enhancement in the stability under an ultraviolet (UV)-assisted acceleration aging test. The significant enhancement in the stability of AZO-based OSCs arises from the tailored absorption of AZO electrode in wavelength < 380 nm, which serves as a UV filter to inhibit an inevitable degradation process in ITO-based OSCs due to the UV irradiation. In order to further investigate the degradation mechanism of OSCs under UV exposure, the change in charge collection characteristics of the OSCs made with ITO/ZnO and AZO/ZnO front cathode before and after UV exposure was examined. It was found that there was an obvious decrease in the charge extraction efficiency of ITO-based OSCs after UV exposure, while there was no observable change in the charge extraction efficiency of OSCs made with AZO/ZnO cathode under the same acceleration aging test. This work demonstrates that AZO is a suitable ITO alternative for application in OSCs, offering an improved device stability, comparable PCE and cell fabrication processes with an attractive commercial potential.

Made available in DSpace on 2014-06-11T19:30:19Z (GMT). No. of bitstreams: 0 Previous issue date: 2013-02-04Bitstream added on 2014-06-13T19:25:43Z : No. of bitstreams: 1 oliveira_ef_me_bauru.pdf: 5543085 bytes, checksum: 90e82da3ce30b958035782b939b534c5 (MD5) / Hoje existe uma necessidade de novos polímeros com propriedades ajustadas para utilização em camadas ativas de céluas solares, uma vez que os materiais mais utilizados ainda não são eficientes, nem suficientemente estáveis, de modo que possam substituir os dispositivos de silício. O poli(3-hexiltiofeno) (P3HT), é um polímero amplamente utilizado em dispositivos fotovoltaicos, e muito importante em células solares. Tem sido relatado modificações na posição 4 das suas unidades monoméricas que levaram a novos polímeros com propriedades diferentes daquele sem modificações. O trabalho que será apresentado visou estudar as propriedades estruturais e ópticas do P3HT e possíveis alterações ocorridas devido às modificações realizadas na posição 4 de suas unidades monoméricas. Tal estudo utilizou ferramentas de cálculo de estrutura eletrônica de materiais, com os métodos PM6 e DFT. Concluímos que o P3HT em solução e no estado sólido não é plantar. Com o nosso modelo para o P3HT, através da conjunção dos métodos ZINDO-S/CIS, obtivemos um pico de absorção óptica teórico em clorofórmio de aproximadamente 385 nm, sendo este em boa concordância com o valor experimental. Em relação às substituições químicas, estudamos teoricamente 15 derivados de P3HT e os cálculos indicaram que é possível obter compostos com uma diminuiçao significativa do gap com estabilidade e solubilidade similares à do P3HT, principalmente com a ligação do átomos de oxigênio ou grupos orgânicos conjugados ao anel tiofênico / Today there is a need new polymers with properties adjusted for use in active layers of solar cells since the most employed materials still are not efficient nor stable enough so that they can replace the silicon devides. The poly(3-hexylthioplene) (P3HT), is a polymer widely used in photovoltaic devices, and very important in solar cells. It has been reported modifications at position 4 of its monomeric units that led to new polymers with different properties than the pristine one. The work that will be presented aimed to study the structural and optical properties of P3HT and possible changes due to chemical substitutions made in position 4 of the monomer units. This study used tools calculating the electronic structure materials, with PM6 and DFT methods. We conclude that the P3HT, in solution and in the solid state, is not planar. With our model for the P3HT, through the combinations of the ZINDO-S/CIS methods, we obtained a theoretical optical absorption peak in chloroform of about 385 nm, in good agreement with the experimental value. In relation to the chemical substitutions, we studied 15 derivatives of P3HT and the calculations indicated that it is possible to obtain compunds with a significant decrease in the gap with stability and solubility similar to that of P3HT, especially with the binding of oxygen atoms or conjugated organic groups to the thiophenic ring