Fluorescence quantum yield role on the Perovskite solar cell efficiency
Document typeMaster thesis
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During the last years, there has been an increased interest toward hybrid organic-inorganic methylammonium lead halide Perovskites due to their suitability for achieving single junction solar cells with efficiencies up to 20%. In the quest for record efficiencies, it is required to minimize the non-radiative recombination of photo-generated carriers in the Perovskite. The balance between radiative and non-radiative recombination of photo-generated carriers in a material can be estimated through measurements of its fluorescence quantum yield (QY), which have been scarcely reported so far in the case of Perovskites. Using an integrating sphere - based fluorescence set-up that we have developed, we report an increase and saturation of the QY of Perovskite films under laser illumination upon increasing the photon flux. We attribute this effect to a decrease in non-radiative recombination induced by the photo-induced filling of defects. We also observe that this filling occurs at the time scale of minutes for a laser photon flux similar to solar illumination conditions. This trend is very similar to that observed for the Voc of Perovskite solar cells, which increases under laser illumination at a comparable time scale. Our work thus suggests a common role of defects in both the QY of the Perovskite films and the efficiency of the Perovskite solar cells. Furthermore, we have developed another fluorescence set-up allowing measurements with angular resolution. We propose that this set-up allows determining a so-called ?intrinsic QY? free from light trapping by total internal reflection and reabsorption in the Perovskite film, and is thus the most suitable for analyzing quantitatively the intrinsic properties of the Perovskite material.
At the moment the use our society makes of the available energy sources is far from optimal. Only a small 5% fraction of the energy used for the electricity production comes from new renewable energy sources. For over several decades, in an attempt to maximize sunlight energy harvesting, researchers in thin film devices have been searching for the optimal materials. Out of the many thin film cell options available one of the most promising is the one based on perovskites. According to the NREL chart the efficiency of such cells almost doubled in just two years. These attrac
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