Διασυνδεδεμένα οργανικά φωτοβολταϊκά

Abstract

Over the last decays the humanity has suffer several problems from the use of fossil fuels for energy production. Issues as the climate changes and the greenhouse effect lead scientists to search for other alternative methods to produce energy. Photovoltaics are one of the most environmentally friendly and “green” method for energy harvesting, taking an advantage an endless power source, the sun. Since the discovery of organic semi-conductive materials the new category of organic photovoltaics becomes an important scientific field of study. Polymer solar cells have been heralded as the photovoltaic (PV) technology solving all the problems current PV technologies are faced with by providing convincing solutions to problems of cost and abundance of the materials that constitute them. In addition their flexibility and light weight can provide alternative ways to power small devices and buildings. In this thesis the basic operating principles of OPVs are analyzed, followed by the state of the art materials, methods structures and power conversion efficiencies of OPVs. A special subchapter is dedicated to tandem organic solar cells explaining all the issues that limit the efficiencies compare to their theoretical efficiency potential. As a reference tandem cell, P3HT:PC60BM was used as an active layer for the bottom cell and Si-PCPDTBT:PC60BM as active layer for the top cell. The thesis is targeting to the optimization of the recombination layer which is the main reason for the charge loss within the tandem device. Based on that PEDOT PH 500 was selected as one of the two counterparts so it can be use as a hole transporter layer of the recombination layer. Using various additives in PH500 we managed to solve three major issues of the recombination layer: the optimum wetting properties for a film formation, low electrical conductivity and the chemical resistivity to of the following layers. The optimum solution of PEDOT PH 500 that is proposed is PEDOT PH 500: PSS 10%: Eg 5%: Z+D 0.5% wt ratio and exhibits excellent wetting properties on top of hydrophobic active layers, increased conductivity by five orders of magnitude compared to our reference PEDOT and exceptional chemical resistance to water and chlorobenzene. The addition of PSS is targeting to increased chemical resistivity of our layer while Eg is proposed for higher conductivities. Zonyl and Dynol as additives are used to decrease the surface tension and allow us coating uniform layers on top of the viii hydrophobic active layers. Finally, our optimized PEDOT has been incorporated in single cell inverted devices with power conversion efficiencies similar and slightly higher compared to our reference inverted device.