Influence of Ambient Working Conditions on the Performance of Planar and Mesoscopic Perovskite Solar Cell Architectures
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Ympäröivien olosuhteiden vaikutus perovskiittiaurinkokennojen suorituskykyyn taso- ja mesorakenteisten kennojen valmistuksessa
Perovskite solar cells can lower the price of the commercial solar cells by half compared to current silicon solar cells, and their research has skyrocketed during the recent years. In only seven years of research, their performance has exceeded 20 %, which makes them the fastest growing photovoltaic technology ever. The main obstacle to the commercialization of the perovskite solar cells is their low stability. The active, light absorbing perovskite material starts to degrade under the influence of light, heat, humidity, and air, decreasing the device performance remarkably. The stability and the device performance of the cells have been improved by optimizing the cell structure, and by replacing the most commonly used perovskite material, CH3NH3PbI3, with multi cation perovskites. In spite of the improved cell stabilities, the most efficient cells are still made in glove box in inert conditions under nitrogen gas. In this Thesis, the influence of oxygen and humidity on the cell fabrication, on the cell performance, namely the cell efficiency and stability, was systematically studied. The influence was investigated for mesoscopic and planar cell architectures using both CH3NH3PbI3 and multi cation perovskite, and two different electron transport materials, SnO2, and TiO2. The performance of the fabricated cells was compared to the data available in the literature for the state-of-the art solar cells, and to those of the devices fabricated at the University of Cologne in inert conditions. The cell performance was analysed quantitatively and qualitatively with IV measurement and SEM characterization, respectively. The cells with triple cation perovskite produced twice as high efficiencies as the cells with CH3NH3PbI3. The best device achieved an efficiency of 9.88 %, which is still far from the state-of-the art cells fabricated in glove box (> 20 %). The fabrication of electron transport layer in the ambient conditions had no influence on the cell performance. On the other hand, the crystallization of perovskite layer was crucially affected by the ambient conditions.