Τα συστατικά μιας ευαισθητοποιημένης φωτοηλεκτροχημικής ηλιακής κυψελίδας μελετήθηκαν ξεχωριστά: ημιαγωγός, χρωστική και ηλεκτρολύτης. Παρασκευάστηκε και χαρακτηρίστηκε ένας στερεός ηλεκτρολύτης με βάση το υψηλού μοριακού βάρους πολυαιθυλενοξείδιο και νανοδομημένη τιτάνια. Ο ηλεκτρολύτης αυτός έφτασε σε ολικές αποδόσεις μετατροπής της ηλιακής ενέργειας σε ηλεκτρική της τάξεως του 4,55%, μία από τις μεγαλύτερες τιμές στη βιβλιογραφία. Χρήση άλλων ημιαγωγών πέρα του διοξειδίου του τιτανίου, όπως το οξείδιο του κασσιτέρου, δεν επέφερε αύξηση της παραπάνω απόδοσης. Νέα σύμπλοκα δισθενούς ρουθηνίου με διαφορετικούς πυριδινικούς υποκαταστάτες χρησιμοποιήθηκαν επίσης ως χρωστικές με αποδόσεις που έφτασαν μόλις το 1.74%. Επίσης, έγινε χρήση της φασματοσκοπίας micro-Raman για να θεμελιωθούν αρχικά συνθήκες συντονισμού και να μελετηθεί η χημειορρόφηση της χρωστικής στον ημιαγωγό. Τέλος μελετήθηκαν οι αλληλεπιδράσεις του οξειδοαναγωγικού ζεύγους με τη χρωστική κατά τη λειτουργία της κυψελίδας. / Τhe components of a dye-sensitized solar cell were thoroughly studied:semiconductor, dye and electrolyte. A novel electrolyte based on high molecular weight polyethylene oxide polymer filled with titania nanoparticles was prepared and characterized. The use of this electrolyte led to significantly high overall efficiencies (solar to electrical power) up to 4.55%, a value that is still one of the highest in literature. The use of different than titania conducting substrates, like tin oxide, did not improve the above efficiencies. Novel ruthenium(II) complexes with diver pyridine ligands were used leading to efficiencies up to only 1.74%. Micro-Raman spectrocopy was also used in order to establish resonance conditions to detect the dye chemisorption on the semiconductor substrate. Finally, the redox couple-dye interactions were thorouglh studied during the cell operation.

Interest in research concerning renewable energy sources has grown in recent decades. In this context, the study of the physical processes that are important in the conversion of solar energy radiation via the photovoltaic effect has increasingly been the topic of theoretical and experimental research. In this thesis, we discuss the photovoltaic effect in pn junctions found in Si solar cells, as well as the photoelectrochemical effect at semiconductor-electrolyte interfaces. Specifically, we propose a new linearizable model for the photocurrent-voltage characteristics of nanocrystalline TiO2 dye sensitized solar cells, as well as ZnO solar cells. We also report predicted values for fill factors. The model uses the Butler-Volmer and Nernst equations to describe the photocurrent-voltage characteristics. A single free parameter of the model controls the fill factor. Upon renormalization, diverse experimental photocurrent-voltage data collapse onto a single universal function. These advances allow the estimation of the complete current-voltage curve and the fill factor from any three experimental data points, e. g., the open circuit voltage, the short circuit current and one intermediate measurement. / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / O interesse em pesquisas sobre fontes de energia renováveis tem crescido nas últimas décadas. Nesse contexto, cada vez mais o estudo dos processos físicos relevantes na conversão da energia da radiação solar, através do efeito fotovoltaico, tem sido alvo de pesquisas experimentais e teóricas. Nesta tese, discutimos o efeito fotovoltaico em junções pn que ocorrem nas células solares de Si, bem como o efeito fotoeletroquímico em interfaces semicondutor-eletrólito. Especificamente, propomos um novo modelo linearizável para as curvas características de fotocorrente-voltagem de células solares de TiO2 nanocristalino sensibilizado por corante, assim como células solares de ZnO. Descrevemos também valores previstos para os fatores de preenchimento. O modelo utiliza as equações de Butler-Volmer e de Nernst para descrever as curvas características de fotocorrente-voltagem. Um único parâmetro livre do modelo controla o fator de preenchimento. Após a renormalização, as curvas com os dados experimentais de fotocorrente-voltagem colapsam em uma única função universal. Estes avanços permitem a estimativa completa da curva de fotocorrentevoltagem e o fator de preenchimento, usando apenas três pontos experimentais, tais como, a voltagem de circuito aberto, a corrente de curto-circuito e uma medida intermediária.