18 Décembre – Thesis defense - Florence Archet

10 h Amphi 3 - ENSCBP (Pessac)

Organic solar cells based on bio-inspired small molecules.

To face the growing needs in energy, renewable energies like solar photovoltaic represent realistic solutions. Photovoltaic energy requires efficient materials to absorb photons and to convert them into electricity. Organic solar cells (OSCs) are based on semiconducting pi-conjugated polymer or small molecules. Current research in this field focuses on three main topics: the reduction of costs, the increase of device lifetime and the increase of power conversion efficiency. This last issue led to an increase in the complexity of OSCs architecture as well as organic semi-conductors, leading to an increase in manufacturing costs. In order to develop sustainable and eco-friendly processes, it is now important to work on cost effective semi-conductors obtained from green synthetic methodology. The aim of this thesis was to develop new bio-inspired organic semi-conductors. These materials are potentially low cost. Molecules studied present donor-acceptor-donor structure. They have the skeleton of curcumine. Curcumine is a natural yellow dye present in curcuma. Acceptor group is boron difluoride. Donor groups vary depending on the curcuminoid derivative. Optoelectronic properties of seventeen semi-conductors were studied. Several of them stood out: those with anthracene groups, those with thiophene derivatives, finally and especially, those with triphenylamine groups. For this last family, the impact on the photovoltaic performances of the ink formulation used for deposition has been deeply studied. Several acceptor materials were tested, as well as ternary blend. For one curcuminoid derivative combined with PC61BM, efficiency above 4% has been achieved with open circuit voltage up to 1.0 V. Due to the very simple chemical structure of the donor, this represents one of the best result reported in literature to our knowledge. Transient species were also studied by ultrafast spectroscopy. The fabrication process was also changed to eliminate halogenated solvent and to enable processing in ambient air like in industrial process. Finally, photovoltaic properties observed are interesting. Nevertheless, they are not sufficient for industrial application due to low hole mobility in these materials.

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