Este trabalho tem como principal objetivo comparar o comportamento fotovoltaico de heterojunções de P3HT/PCBM e heterojunções de P3HT/PCBM contendo nanopartículas de ouro (P3HT/PCBM/Au nanop). Inicialmente foi encontrada a melhor condição para deposição dos filmes de P3HT/PCBM, através do estudo do efeito do solvente, da temperatura e pressão durante a formação do filme de P3HT. Os resultados mostram que a melhor organização estrutural é obtida quando o polímero é disperso em clorobenzeno, e solidificado a temperatura 110°C em condição de baixa pressão. Os materiais foram caracterizados por voltametria cíclica, espectroscopia Uv-vis, espectroscopia no infravermelho, microscopia eletrônica de transmissão e difratometria de raios-x. Os dispositivos montados foram caracterizados por curvas de corrente versus potencial e eficiência de conversão de fóton incidente. Com o objetivo de avaliar o efeito das nanopartículas metálicas na estabilidade estrutural do dispositivo, foram realizadas obtidos espectros de FTIR dos filmes de P3HT na presença e na ausência de nanopartículas de ouro, após diferentes períodos de exposição à luz. Os filmes de P3HT/PCBM/Aunanop apresentaram maior absorção de luz na região do visível que resultou em maior eficiência de geração de fotocorrente quando comparada a P3HT/PCBM. Ainda através dos gráficos de IPCE foi observado um aumento da geração de fotocorrente na mesma região espectral do modo plasmônico. Através destes resultados nós observamos que a presença das nanoparticulas metálicas melhora a geração de fotocorrente, aumentando a XV intensidade de luz absorvida e o aprisionamento da luz dentro da camada fotoativa. / The main goal of this work was to compare the effect of gold nanoparticles on the photovoltaic properties of the P3HT/PCBM heterojunction. Initially we have studied the best condition to obtain the P3HT/PCBM films evaluating the effect of solvent, temperature and pressure during the formation of the film. The results show that the best structural organization is obtained from in chlorobenzene, at 110 oC at low pressure condition. The materials were characterized by cyclic voltammetry, Uv-vis spectroscopy, infrared spectroscopy, transmission electron microscopy and x-ray diffractometry. The assembled devices were characterized by current versus potential curves and incident photon to current efficiency. Aiming to evaluate the effect of gold nanoparticles on the structural stability of the device, we have performed FTIR experiments of the films with and without gold nanoparticles after different exposition periods. The P3HT/PCBM/Au nanop film presented improved optical behavior and enhanced photocurrent generation when compared to P3HT/PCBM, in addition by IPCE we have observed improved generation of photocurrent in the region near the absorption range of the gold nanoparticles. From the results we observe that the presence of gold nanoparticles improve the generation of photocurrent, by increasing light absorption and improving light entrapment in the photoactive film.

Este trabalho tem como principal objetivo comparar o comportamento fotovoltaico de heterojunções de P3HT/PCBM e heterojunções de P3HT/PCBM contendo nanopartículas de ouro (P3HT/PCBM/Au nanop). Inicialmente foi encontrada a melhor condição para deposição dos filmes de P3HT/PCBM, através do estudo do efeito do solvente, da temperatura e pressão durante a formação do filme de P3HT. Os resultados mostram que a melhor organização estrutural é obtida quando o polímero é disperso em clorobenzeno, e solidificado a temperatura 110°C em condição de baixa pressão. Os materiais foram caracterizados por voltametria cíclica, espectroscopia Uv-vis, espectroscopia no infravermelho, microscopia eletrônica de transmissão e difratometria de raios-x. Os dispositivos montados foram caracterizados por curvas de corrente versus potencial e eficiência de conversão de fóton incidente. Com o objetivo de avaliar o efeito das nanopartículas metálicas na estabilidade estrutural do dispositivo, foram realizadas obtidos espectros de FTIR dos filmes de P3HT na presença e na ausência de nanopartículas de ouro, após diferentes períodos de exposição à luz. Os filmes de P3HT/PCBM/Aunanop apresentaram maior absorção de luz na região do visível que resultou em maior eficiência de geração de fotocorrente quando comparada a P3HT/PCBM. Ainda através dos gráficos de IPCE foi observado um aumento da geração de fotocorrente na mesma região espectral do modo plasmônico. Através destes resultados nós observamos que a presença das nanoparticulas metálicas melhora a geração de fotocorrente, aumentando a XV intensidade de luz absorvida e o aprisionamento da luz dentro da camada fotoativa. / The main goal of this work was to compare the effect of gold nanoparticles on the photovoltaic properties of the P3HT/PCBM heterojunction. Initially we have studied the best condition to obtain the P3HT/PCBM films evaluating the effect of solvent, temperature and pressure during the formation of the film. The results show that the best structural organization is obtained from in chlorobenzene, at 110 oC at low pressure condition. The materials were characterized by cyclic voltammetry, Uv-vis spectroscopy, infrared spectroscopy, transmission electron microscopy and x-ray diffractometry. The assembled devices were characterized by current versus potential curves and incident photon to current efficiency. Aiming to evaluate the effect of gold nanoparticles on the structural stability of the device, we have performed FTIR experiments of the films with and without gold nanoparticles after different exposition periods. The P3HT/PCBM/Au nanop film presented improved optical behavior and enhanced photocurrent generation when compared to P3HT/PCBM, in addition by IPCE we have observed improved generation of photocurrent in the region near the absorption range of the gold nanoparticles. From the results we observe that the presence of gold nanoparticles improve the generation of photocurrent, by increasing light absorption and improving light entrapment in the photoactive film.

Orientador: Ana Flávia Nogueira / Tese (doutorado) - Universidade Estadual de Campinas, Instituto de Química / Made available in DSpace on 2018-08-23T23:53:53Z (GMT). No. of bitstreams: 1 Freitas_FlavioSantos_D.pdf: 16885434 bytes, checksum: 48b960051e69118d4e3bbf7bc096a552 (MD5) Previous issue date: 2013 / Resumo: Este trabalho apresenta a síntese de moléculas carboxiladas e sua utilização como agentes compatibilizantes em sistemas híbridos inorgânico/orgânico. A caracterização e aplicação das interfaces destes sistemas híbridos de dióxido de titânio com poli(3-hexiltiofeno) (TiO2/P3HT) e silício monocristalino com poli(3-hexiltiofeno) (Si/P3HT) também foram estudadas. No primeiro sistema, TiO2/P3HT, a modificação superficial do TiO2 foi efetuada com três moléculas carboxiladas: ácido 2-tiofenocarboxílico (TCA), ácido 2-tiofenoacético (TAA) e ácido 2,4-tiofenodicarboxílico (TDA). Essas modificações demostraram que a molécula TAA apresenta melhor compatibilidade na interface, evidenciada por estudos fotofísicos de Espectroscopia de Absorção Transiente (TAS) e medidas de ângulo de contato. A célula solar com TAA (configuração invertida) apresentou eficiência de 0,03%, três vezes maior que a obtida no dispositivo padrão. Com a inserção do corante N719 na superfície do TiO2, a eficiência alcançou valores superiores a 1%. A eficiência dos dispositivos chegou a 1,35% com a inserção na camada de P3HT de nanopartículas de TiO2 na forma de bastão (TiO2 NB/TAA). Essa modificação da camada polimérica mostrou que o TiO2 NB/TAA apresentou propriedades ligeiramente superiores nos experimentos de fotoeletroquímica quando comparado com nanopartículas sintetizadas no formato esférico (TiO2 NE). Além disso, a técnica de Espalhamento de Raios-X a Baixo Ângulo (SAXS) mostrou que as nanopartículas TiO2 NB/TAA e TiO2 NE encontram-se distribuídas de forma homogênea pela matriz de P3HT. No segundo sistema, as células solares de Si/P3HT foram obtidas a partir de reações que modificaram a interface dos materiais. A adsorção química da molécula TAA sobre o óxido nativo (Si/SiOx/TAA) e a reação do grupo superficial Si-Cl com o reagente de Grignard brometo de tiofeno-magnésio (Si/Tiofeno) foram respectivamente caracterizadas por Espectroscopia de Infravermelho (FTIR) e Espectroscopia de Fotoelétrons por Raios-X (XPS). A contribuição do P3HT para o dispositivo foi avaliada a partir da comparação com uma junção Schottky (Al/Si/Au). Os valores de VOC obtidos nas células solares na presença de P3HT foram similares (~0,4 V) e superiores ao obtido no dispositivo sem o polímero (~0,2 V), evidenciando o domínio da junção Si/P3HT para as propriedades fotovoltaicas. O dispositivo Si/SiOx/TAA apresentou grande resistência em série, com eficiência de conversão de energia inferior a 0,5%. Porém, com a configuração Al/Si/Tiofeno/P3HT/Au, as células solares alcançaram valores de eficiência de 5,76%. A eficiência superior foi relacionada com a melhor adesão e compatibilidade entre o Si e o P3HT a partir de imagens de SEM / Abstract: This work presents the synthesis of carboxylated molecules and their use as compatibilizer agents in hybrid inorganic/organic systems. Characterization and application of the interfaces of those hybrid systems comprising titanium dioxide with poly(3-hexylthiophene) (TiO2/P3HT) and monocrystalline silicon with poly(3-hexylthiophene) (Si/P3HT) will also be described. In the former system, TiO2/P3HT, the TiO2 surface was modified with three molecules: 2-thiophenecarboxylic acid (TCA), 2-thiopheneacetic acid (TAA) and 2,4- thiophenedicarboxylic acid (TDA). Transient Absorption Spectroscopy (TAS) photophysical studies and contact angle measurements demonstrated that TAA presents the best compatibility in the interface. Solar cells modified with TAA, set up in inverted configuration, showed 0.03% of overall energy conversion efficiency, which is three times larger than the one obtained from a standard device. Replacing TAA by N719 dye on TiO2 surface increased the efficiency, achieving values higher than 1%. Inserting TiO2 rod-shaped nanoparticles (TiO2 NB/TAA) on P3HT layer of the latter system resulted in 1.35% overall efficiency. Photoelectrochemical experiments demonstrated that this modification using TiO2 NB/TAA increases exciton separation rate and conductivity properties slightly enhanced compared to spherical nanoparticles (TiO2 NE/TAA). Small-Angle X-ray Scattering (SAXS) showed that TiO2 NB/TAA and TiO2 NE nanoparticles are homogeneously distributed in the P3HT matrix. In the Si/P3HT hybrid system, the inorganic/organic interface was modified through chemical adsorption of TAA molecules on the native oxide (Si/SiOx/TAA) and a reaction of the surface Si-Cl groups with Grignard reagent 2-thiophene-magnesium bromide (Si/Tiofeno). Both reactions were characterized using Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). The contribution of P3HT to the p-n junction formation in the photovoltaic device was evaluated from a comparison with a Schottky junction (Al/Si/Au). The VOC values obtained with P3HT were similar among the experiments (around 0.4 V) and higher than without the polymer (around 0.2 V). This observation highlights the dominance of Si/P3HT for photovoltaic properties. The Si/SiOx/TAA device exhibited a high series resistance, with energy conversion efficiency lower than 0.5%. However, using Al/Si/Tiofeno/P3HT/Au configuration, the solar cells reached 5.76% efficiency. The higher values might be related to a better adhesion and compatibility between Si and P3HT, which was observed from SEM images / Doutorado / Quimica Inorganica / Doutor em Ciências

As part of the SUNRISE project (Semiconductors Using Nanostructures for Record Increases in Solar-cell Efficiency), high efficiency, III-V semiconductor, quantum-dot-enhanced, triple-junction solar cells designed and manufactured by Cyrium Technologies Inc. were integrated into OPEL Solar, MK-I, Fresnel-lens-based, 550x concentrating modules carried on a dual axis tracker. Over its first year of operation 1.8 MWh of AC electrical energy was exported to the grid. Measurements of the direct and indirect components of the insolation, as well as the spectral irradiance of light incident on the demonstrator in Ottawa, Canada are presented. The system efficiency is measured and compared to that predicted by a system model to identify loss mechanisms so that they can be minimized in future deployments.

A novel approach to the design of multi-junction solar cells on silicon substrates for 1-sun applications is described. Models for device simulation including porous silicon layers are presented. A silicon bottom subcell is formed by diffusion of dopants into a silicon wafer. The top of the wafer is porosified to create a compliant layer, and a III-V buffer layer is then grown epitaxially, followed by middle and top subcells. Due to the resistivity of the porous material, these designs are best suited to high efficiency 1-sun applications. Numerical simulations of a multi-junction solar cell incorporating a porous silicon compliant membrane indicate an efficiency of 30.7% under AM1.5G, 1-sun for low threading dislocation densities (TDD), decreasing to 23.7% for a TDD of 10^7 cm^-2.

Freshwater scarcity and clean energy shortage are two grand challenges to global sustainable development. The inextricably interconnected water-energy nexus is being increasingly felt globally owing to the massive water used for electricity generation and huge amount of energy consumed in water desalination. This dissertation investigated the utilization of the waste heat of the solar cell to produce fresh water. This is achieved by constructing a multistage membrane distillation device (MSMD) at the backside of the solar cell to efficiently utilize its heat and it is capable of recycling the latent heat of the vapor condensation in each distillation stage. The first generation photovoltaic-membrane distillation (PV-MD) device exhibits a clean water production rate of 1.64 kg/m2 h with the solar cell temperature of 58 oC in a 3-stage device under one-sun radiation. However, some concentrated seawater can be produced from the PV-MD owing to its cross-flow design. To this end, an evaporative crystallizer is designed beneath the PV-MD, which can reuse the low-grade latent heat of vapor condensation in the last stage of the MSMD to evaporate the produced concentrated seawater, realizing zero liquid discharge. In addition, a theoretical model was also established to enhance the clean water production rate and reduce the solar cell temperature, which guides us to select a hydrophobic membrane with a thickness of 0.1 mm and porosity of 0.86 to fabricate the second generation photovoltaic-membrane distillation-evaporative crystallizer (PV-MD-EC) device. We experimentally demonstrate that a 5-stage PV-MD-EC device can desalinate seawater at a rate of ~2.45 kg m-2 h-1 with a lower solar cell temperature of ~48oC. The electricity generation efficiency of the solar cell is also enhanced by ~8% owing to its reduced temperature. A trade-off exists between the clean water production performance and material cost of the MSMD because a higher energy efficiency is at the expense of more stages applied. A low-cost and highly flexible 8-stage paper-based MSMD (P-MSMD) is further designed and fabricated and it showed a clean water production rate of 3.61 kg/m2 h for seawater desalination. This work sheds light on the design and fabrication of a composite system capable of achieving the simultaneous production of electricity and clean water with solar energy as an only energy source. Owing to their low barrier of entry, the devices reported in this dissertation are well suited to provide off-grid electricity and freshwater in a decentralized manner for point of consumption locations especially off-grid communities and communities with small- to medium-sized population even with challenging economic conditions.

>Magister Scientiae - MSc / Without reverting to encapsulation, organic bulk - heterojunction solar cells can be protected from the oxidation of the highly reactive low work function cathode metal electrode, by the deposition of metal oxide buffer layers onto an indium-tin oxide (ITO) substrate. The zinc-oxide (ZnO) or titanium dioxide (TiO2) layer can serve as an electron collecting contact. In such a case the ordering of layer deposition is inverted from the traditional layer sequencing, using an additional effect of the metal oxide layer acting as a hole blocking contact

This thesis is dedicated to studies of the excited-state dynamics in organic molecular systems for solar energy conversion by employing time-resolved experimental techniques. Organic photovoltaic (OPV) devices have received significant attention in the past decade and reaching record high power conversion efficiencies (PCE) above 17%. An essential step towards reaching the predicted PCE limit of 25.5% is to develop a comprehensive picture of the photophysical processes, specifically the loss processes, in OPV devices. It is the aim of this thesis to investigate and understand the fate of excited-states in organic electron donor/acceptor systems by ultrafast spectroscopic techniques, specifically, to reveal the interplay between energy and charge transfer processes. The first part deals with the identification of different polymorphs in a diketopyrrolopyrrole-based (DPP) polymer. Applying time-resolved photoluminescence (TRPL) measurements to the polymer dissolved in different solvent mixtures and using multivariate curve resolution (MCR) to deconvolute the ground-state absorption spectra reveals the co-existence of an amorphous (α) and two semi-crystalline (β1 and β2) polymer phases. The OPV device performance is shown to increase by the additional absorption of the β2 phase. The second part compares the efficiency of direct and energy transfer-mediated charge generation in prototypical donor-acceptor dyads that use as the electron donor triangulene derivatives chemically linked to the electron acceptor perylenediimide (PDI) block via oligophenylene spacers of different lengths. Charge generation efficiencies are found to be similar and increase with the donor-acceptor spatial separation. A combination of transient absorption (TA) measurements and computation of the dyad’s excited-state landscape revealed the presence of “optically-dark” excited-states that are populated by ultrafast donor-acceptor energy transfer prior to hole (back) transfer. The last part of the dissertation uses TRPL, TA, and time-delayed collection field (TDCF) measurements alongside MCR analysis to provide a comprehensive analysis of the yield of individual photophysical processes in OPV devices. A systematic methodology is proposed and tested on two all-polymer BHJ devices used as model systems. The experimental findings are supported by successful simulation of the solar cells’ JV characteristics using the spectroscopically-determined kinetic parameters. More generally, this approach can be used to quantify efficiency-limiting processes in other donor-acceptor BHJs.

In the last decade, organic photovoltaics (OPVs) have been attracting much attention for their low cost, and feasibility of mass production in large-area modules. Reported power conversion efficiencies (PCE) of organic solar cells have reached more than 10%. These promising PCEs can be realized by uncovering important principles: (1) rational molecular design, (2) matching of the material energy level, (3) favorable morphology of donor-acceptor (D/A) network, (4) higher carrier mobilities, and (5) suppression of charge recombination within the bulk heterojunction (BHJ). Though these key properties are frequently stated, the relationships between these principles remain unclear, which motivates us to fill these gaps. In the beginning, we show that changing the sequence of donor and acceptor units of the benzodithiophene-core (BDT) SM donors critically impacts molecular packing and charge transport in BHJ solar cells. Moreover, we find out that by adding small amount of the external solvent additive, the domain size of the SMFQ1 become relatively smaller, resulting in the FF enhancement of ~70% and thus pushing PCE to >6.5%. To further improve the device performance, we utilize another technique of device optimization: Solvent Vapor Annealing (SVA). Compared with solvent additive, the SVA creates a solvent-saturated environment for SMs to re-arrange and crystalize, leading to PCE of >8%, with nearly-free bimolecular recombination. When the systems are shifted from fullerene acceptors to nonfullerene acceptors, using solvent additives in indacenodithiophene-core (IDT) systems significantly reduces the domain size from >500nm to <50nm and also allows the SM donors to orderly packed, rising the PCE from <1% to 4.5%. Furthermore in a similar IDT-based system, it shows unexpectedly high VOC and low energy loss, and high PCE > 6% can be reached by employing the dimethyl disulfide (DMDS) as the SVA solvent to re-organize the morphology from excessive mixing to ordered phase-separated D/A network. Lastly, taking advantage of the distinct and complementary absorption of fullerene and nonfullerene acceptors, we show that the SM ternary system successfully realizes the high PCE of 11%, good air stability, and scalable property.

The study of the new materials potentially usable for organic photovoltaic and electronics are getting very important from the point of ecological and financial view. Organic electronic devices are getting more and more popular and it is only up to us to search for the new ones that are able to improve their physical properties. The aim of this thesis is to search for materials like have been mentioned above which have very good semiconducting properties. Solutions of pure materials and its mixtures with different concentrations of fullerene have been investigated by ultra-violet spectroscopy, classical fluorescence and time resolved spectrometry. Mainly, were studied the influence of the central atom and side substituents for the optical and electronical properties of our materials of interest. With adding fullerene was observed quenching phenomena of the fluorescence, because all these new materials show usually high photoluminescence. Based on the given results, the most suitable materials had been chosen to provide trial of making organic solar cell, and therefore investigated by the mean of electric measurements (direct current).