Η τεχνολογία φωτοβολταϊκών λεπτών φιλμ πυριτίου συνδυάζει χαμηλό κόστος παραγωγής, μικρό χρόνο ενεργειακής απόσβεσης και χαμηλές απαιτήσεις σε πρώτες ύλες. Ωστόσο, μειονεκτήματα όπως η χαμηλή απόδοση και η φωτοεπαγόμενη υποβάθμιση του άμορφου πυριτίου καθιστουν την τεχνολογία αυτή λιγότερο ανταγωνιστική σε σχέση με τα φωτοβολταϊκά κρυσταλλικού πυριτίου. Για να αυξηθεί η απόδοση χρησιμοποιούνται περισσσότερα ενεργά στρώματα οδηγώντας σε φωτοβολταϊκά πολυεπαφών. Συνδυάζοντας άμορφο και μικροκρυσταλλικό πυρίτιο, με ενεργειακό χάσμα περίπου 1.7eV και 1.1eV αντίστοιχα προκύπτει η διάταξη a-Si/μc-Si. Στην παρούσα εργασία παρουσιάζεται εκτενώς το φωτοβολταϊκό a-Si/μc-Si, το οποίο αναφέρεται και ως micromorph. Μελετώνται τα χαρακτηριστικά των ενεργών υλικών από τα οποία αποτελείται και οι ιδιότητες εκείνες που απαιτούνται για υψηλής ποιότητας επιστρώσεις. Παρουσιάζονται τα ιδιαίτερα χαρακτηριστικά της τεχνολογίας φωτοφολταϊκών λεπτών φιλμ πυριτίου και οι διαφορές της με τις υπόλοιπες τεχνολογίες. Μελετάται επίσης η δομή της διάταξης a-Si/μc-Si και η έρευνα που αφορά τις τεχνικές βελτιστοποίησής της και την αύξηση της απόδοσης. Στη συνέχεια γίνεται πειραματική μελέτη για τις επιδόσεις ενός φωτοβολταϊκού πλαισίου a-Si/μc-Si σε συνθήκες εξωτερικού χώρου, σε σύγκριση με φωτοβολταϊκά πλαίσια άλλων τεχνολογιών πυριτίου, ενός μονοκρυσταλλικού και ενός άμορφου. Το πλαίσιο a-Si/μc-Si της εταιρείας Heliosphera που μελετήθηκε έχει υποστεί την αναμενόμενη φωτοεπαγόμενη υποβάθμιση και η απόδοσή του σε πρότυπες συνθήκες βρέθηκε ίση με 8.14% με μια μείωση 8.5% από την αρχική απόδοση. Μελετήθηκε η εξάρτηση της επίδοσης των φωτοβολταϊκών πλαισίων από την μεταβολή της γωνίας πρόσπτωσης, τη θερμοκρασία και την ένταση της ηλιακής ακτινοβολίας. Επιβεβαιώθηκε πειραματικά η μείωση της απόδοσης του πλαισίου a-Si/μc-Si με την αύξηση της αέριας μάζας, κάτι που παρατηρήθηκε και για το πλαίσιο αμόρφου πυριτίου. Η μελέτη φωτοβολταϊκών πλαισίων σε συνθήκες εξωτερικού χώρου θα οδηγήσει στην κατανόηση των διαφορών μεταξύ διαφορετικών τεχνολογιών και στη σημασία των κλιματολογικών συνθηκών ενός τόπου στην επιλογή των φωτοβολταϊκών πλαισίων για κάποια εγκατάσταση. / Thin film silicon photovoltaic technology combines low production cost, short energy payback time and low demands of raw materials. However, drawbacks as low efficiency and light induced degradation make this technology less competitive in regard to crystalline silicon solar cells. In order to increase the efficiency, more active layers are used leading to multijuction photo voltaics. Combining amorphous and microcrystalline silicon with energy bandgap of 1.7eV and 1.1eV correspondingly, results in the device a-Si/μc-Si.. In this work a-Si/μc-Si, which is also referred as micromorph, is thoroughly presented. The characteristics of its active materials and the properties required for device quality layers are studied. The specific properties of thin film silicon photovoltaics are presented along with the differences with other technologies. The structure of the a-Si/μc-Si device and the research for its optimization techniques and efficiency increase are also studied. An experimental study takes place for the performance of an a-Si/μc-Si photovoltaic module in outdoor conditions, in comparison with other silicon photovoltaic technologies, as monocrystalline and amorphous silicon. The module a-Si/μc-Si of the company “Heliosphera” that was studied has undertaken the prospective light induced degragation and its efficiency in standard conditions was 8.14% with a reduction of 8.5% from the initial efficiency. The performance of the photovoltaic modules was studied under the effect of shifts in the angle of incidence, temperature changes and changes in the solar irradiation intensity. The reduction in the efficiency of the a-Si/μc-Si module with the increase of the air mass was experimentally confirmed and was also verified for the amorphous silicon module. The study of photovoltaic modules in outdoor conditions will lead in better understanding the differences among various technologies and the effect of the climate conditions of a location on the choice of the photovoltaic modules for an installation.

[pt] O termo de ondas milimétricas refere-se à porção do espectro eletromagnético com frequências entre 30 e 300 GHz, correspondente a comprimentos de onda de 10 até 1 mm. As características das ondas milimétricas diferem das microondas e das ondas infravermelhas, e são estas diferenças que fazem com que um sistema de ondas milimétricas seja o candidato ideal para algumas aplicações. Em anos passados a falta e o alto custo de fontes, dispositivos, componentes e instrumentação adequada para esta faixa de frequências, levaram a um progresso muito lento nesta área. Atualmente, com o planejamento da nova geração de comunicações móveis, isto está mudando e dispositivos nesta faixa de frequências estão sendo comercializados mundialmente. A faixa de operação pensada para a nova geração de comunicações móveis 5G vai de 24.25 GHz até 86 GHz. No Brasil, as faixas consideradas são de 24.25 GHz até 27.5 GHz e possivelmente de 37 GHz até 40 GHz. Neste trabalho vamos explorar a faixa de frequências entre 26.5 GHz e 40 GHz. Esta faixa já está sendo estudada por vários pesquisadores, porém ainda não existe muita literatura sobre resultados de medições em diferentes ambientes compostos por diferentes materiais. Neste trabalho serão apresentados resultados de medições de perda de penetração e coeficientes de reflexão em materiais de construção usuais. Também serão apresentados resultados de medições de perda de propagação em ambientes abertos (outdoor), realizadas no campus da PUC-Rio, e um modelo de predição desenvolvido com base nos resultados. Resultados de medições em ambientes fechados (indoor), realizadas no Centro de Estudos em Telecomunicações e num prédio da mesma universidade, também serão apresentados ao final desta tese. / [en] The millimeter wave term refers to the portion of the electromagnetic spectrum with frequencies between 30 and 300 GHz corresponding to wavelengths from 10 to 1 mm, that commercially is known as millimeter waves frequencies.The characteristics of millimeter waves differ from microwaves and infrared, and these differences make millimeter wave systems ideal candidates for some applications. In the past years, the lack and high cost of sources, devices, components and adequate instrumentation for this frequency range have caused a low progress. However, in the currently planning of the new generation of mobile communication system this is changing, and devices in this frequency range are being marketed worldwide. The frequency range proposed for new generation of mobile communication varies from 24.25 GHz to 86 GHz. In Brazil, the bands proposed are 24.25 GHz to 27.5 GHz and also from 27 GHz to 40 GHz. In this work, we will explore the range from 26.5 GHz to 40 GHz, due to equipment limitations. This frequency range is already being studied by several researchers. However, there is not extensive literature on measurement results in different environments or with different materials. This work will present results of penetration loss measurements in different materials, and the reflection coefficients for each material. Also, outdoor measurements made in the university campus will be presented and an improved path loss prediction method developed. Indoor measurements results, made in the Center of Studies in Telecommunications and in another building in the campus will also be presented.