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As células foto voltaicas orgânicas ou células de Gräetzel (depois do seu descobridor) são aparelhos para a colecta de energia solar que utilizam um semicondutor inorgânico e uma molécula orgânica. Dita molécula orgânica é capaz de excitar-se na presença de radiação electromagnética e ceder esta energia através da doação de electrões a este semicondutor.
Embora estas estruturas e o seu processo de fabrico sejam relativamente pouco onerosas, o aproveitamento da energia solar é ainda muito baixo. Para além desta deficiência, os corantes sintéticos sofrem de “bleaching” ou então são reduzidos ou oxidados facilmente quando não conseguem transferir a energia que foi absorvida ou quando é difícil voltar ao estado original por dificuldades no completamento de circulação de electrões.
Neste trabalho pretende-se então estudar o comportamento de moléculas e misturas complexas de moléculas com capacidade para serem excitadas pela luz solar. Como a dita xcitação promove a transferência de um electrão, este processo será seguido pela técnica
de Voltametria cíclica. Como substâncias absorventes de luz utilizaremos compostos naturais (principalmente flavonóides) puros, ou então na forma de complexos naturais extraídos de algumas plantas. Estas misturas de corantes serão extractos aquosos (infusões) de casca de laranja e limão assim como extractos de folhas de cerejeira, com o objectivo de proporcionar lternativas aos flavonóides utilizados neste estudo. A caracterização voltamétrica desta célula é feita em diferentes formas de iluminação. Sobre a célula assim formada faz-se incidir rimeiro luz de lâmpadas fluorescentes, depois luz ultra violeta e por fim sem qualquer tipo de luz incidente.
Na base do fabrico da variante mais clássica destas células está o semicondutor óxido de itânio (TiO2), por ser uma substância muito comum e barata e com propriedades semicondutoras notáveis. Uma forma comum de melhorar a eficiência deste material é introduzir dopantes com o intuito de melhorar a eficiência do processo de transferência electrónica.
Um segundo objectivo deste trabalho é o estudo de sistemas semicondutor/molécula foto activa. Semicondutores como ZnO, TiO2 e TiO2 dopado serão então estudados. O gels de TiO2 ou o TiO2 dopado serão depositados sobre lâminas de vidro comum, nas quais foi anteriormente depositado uma película de alumínio que serve de condutor (eléctrodo egativo). Uma outra variante será a utilização de óxido de zinco, um semicondutor de baixo custo que por sua vez vai ser depositado em lâminas de alumínio comercial.
A nossa célula foto electroquímica será então formada por moléculas de corante, uma lâmina e um semicondutor (que funcionará como eléctrodo de trabalho), com ou sem electrólito/catalizador (solução de iodo/iodeto), e eléctrodos de referência de Ag/AgCl, e outro auxiliar de grafite.
Um outro objectivo é fazer um pequeno estudo sobre influencia do catalisador I2/etilenodiamina no comportamento electroquímico da célula, de forma a poder utilizar o solvente (etilenodiamina) com menor volatilidade do que a água, que é empregada no par I2/I3.m A importância deste facto prende-se com a limitada vida destas células quando o electrólito/solvente é evaporado pelas altas temperaturas da radiação incidente.
The organic photovoltaic cells or Graëtzel cells (after its discoverer) are devices for collecting olar energy using an inorganic semiconductor and an organic molecule. That organic molecule must be able to be excited by electromagnetic radiations and transfer this energy through the donation of electrons in this semiconductor. Although these structures and their manufacturing process are relatively inexpensive, the use of solar energy is still very low. In addition to this deficiency, synthetic dyes suffer from "bleaching" or they are reduced or oxidized easily when they cannot transfer the energy that was absorbed or when it is difficult to return to its original state by difficulties in completing the movement of electrons. This work intends to study the behavior of molecules and complex mixtures of molecules capable of being excited by sunlight. As the photonic excitation promotes the transfer of an electron, this process will be followed by cyclic voltammetry technique. As light-absorbing substances here were utilized natural compounds (mainly flavonoids), in pure form or as natural complexes extracted from some plants. These dyes are mixtures of aqueous extracts (infusions) of orange peel and lemon as well as extracts from leaves of cherry, with the aim of providing alternatives to the flavonoids used in this study. The voltammetric characterization of this cell is made in different forms of lighting. Thus formed on the cell it is focused first light of fluorescent lamps, ultraviolet light and then finally without any incident light. On the basis of production of the classic variant of these cells the semiconductor titanium oxide (TiO2) is used. This oxide is very common and inexpensive and with outstanding emiconducting properties. A common way to improve efficiency is to introduce dopants in order to improve the efficiency of electron transfer. A second objective of this work is the study of semiconductor systems / photo active molecule. Semiconductors such as ZnO, TiO2 doped TiO2 and will then be studied. TiO2 or TiO2 doped gels will be deposited on ordinary glass slides. In these slides were previously deposited aluminum films as conductor (electrode negative). Another variant is the use of zinc oxide, a semiconductor low cost which in turn was deposited in commercial aluminum sheets. Our photo-electrochemical cell is then formed by dye molecules, a semiconductor film (which act as working electrode), with or without electrolyte / catalyst (solution of iodine / iodide), and eference electrodes of Ag / AgCl and other auxiliary graphite. Another objective is to make a short study on the influence of catalyst I2/ethylendiamine on the electrochemical behavior of the cell. This solvent (ethylenediamine) has lower volatility than water, which is used in pair I2/I3-. The importance of this study relates to the limited life of thesecells when the electrolyte / solvent is evaporated by the heat of the incident radiation.
The organic photovoltaic cells or Graëtzel cells (after its discoverer) are devices for collecting olar energy using an inorganic semiconductor and an organic molecule. That organic molecule must be able to be excited by electromagnetic radiations and transfer this energy through the donation of electrons in this semiconductor. Although these structures and their manufacturing process are relatively inexpensive, the use of solar energy is still very low. In addition to this deficiency, synthetic dyes suffer from "bleaching" or they are reduced or oxidized easily when they cannot transfer the energy that was absorbed or when it is difficult to return to its original state by difficulties in completing the movement of electrons. This work intends to study the behavior of molecules and complex mixtures of molecules capable of being excited by sunlight. As the photonic excitation promotes the transfer of an electron, this process will be followed by cyclic voltammetry technique. As light-absorbing substances here were utilized natural compounds (mainly flavonoids), in pure form or as natural complexes extracted from some plants. These dyes are mixtures of aqueous extracts (infusions) of orange peel and lemon as well as extracts from leaves of cherry, with the aim of providing alternatives to the flavonoids used in this study. The voltammetric characterization of this cell is made in different forms of lighting. Thus formed on the cell it is focused first light of fluorescent lamps, ultraviolet light and then finally without any incident light. On the basis of production of the classic variant of these cells the semiconductor titanium oxide (TiO2) is used. This oxide is very common and inexpensive and with outstanding emiconducting properties. A common way to improve efficiency is to introduce dopants in order to improve the efficiency of electron transfer. A second objective of this work is the study of semiconductor systems / photo active molecule. Semiconductors such as ZnO, TiO2 doped TiO2 and will then be studied. TiO2 or TiO2 doped gels will be deposited on ordinary glass slides. In these slides were previously deposited aluminum films as conductor (electrode negative). Another variant is the use of zinc oxide, a semiconductor low cost which in turn was deposited in commercial aluminum sheets. Our photo-electrochemical cell is then formed by dye molecules, a semiconductor film (which act as working electrode), with or without electrolyte / catalyst (solution of iodine / iodide), and eference electrodes of Ag / AgCl and other auxiliary graphite. Another objective is to make a short study on the influence of catalyst I2/ethylendiamine on the electrochemical behavior of the cell. This solvent (ethylenediamine) has lower volatility than water, which is used in pair I2/I3-. The importance of this study relates to the limited life of thesecells when the electrolyte / solvent is evaporated by the heat of the incident radiation.