THESIS TITLE : Synthesis and optical properties of 3D perovskites for photovoltaïcs and OLEDs
Hybrid perovskite crystals having the formula (R-NH3)2MX4 or (H3N-R-NH3)M4, with R an organic group, M a divalent metal such as Pb2+ and X an halogen ion such as Cl, Br or I, have attracted much attention since 1990 ‘s years due to the particular optical properties of this semiconductor, which is a good candidate to be introduced in opto-electronic devices like OLEDs (Organic Light Emitting Diodes), OFETs (Organic Field Effet Transistors) and more recently photovoltaic devices . Since 2 years, works about hybrid organic-inorganic perovskites provide an explosion of the performance of these low cost solar cells, they now compete with the silicon solar cells : in fact, after only two years of research, the obtained efficiency is already 20% ! Moreover, an article published in 2014 shows the ability of the 3D perovskites to emit some white light , the hybrid perovskites are thus also very good candidates for a new line of materials for OLED lighting. In summary, this new material represents a true breakthrough in the physics of materials.
In this particular active context, and relying on our 10 years expertise in 2D perovskites (R-NH3)2PbX4, we propose the synthesis of new hybrid perovskites. Firstly, we propose to synthesize 3D perovskite alloys. Mixing halogen ions allows to tune continuously the energy gap of these semiconductors, which is interesting for both the collection and the emission of light. The substitution of lead by another metallic cation, a divalent one or a cation with another oxydation degree, will allow to explore the conduction properties of the perovskites and to treat the environnemental problem posed by lead.
In order to improve the ability to collect solar light by the 3D perovskite, we propose to functionalize the organic part of the material. Relying on the activation experience of the 2D perovskites by introducing a fluorophore in the structure of the molecular crystal, and thanks to our great knowledge about the self-assembly of these materials, we will be able to find the convenient molecules for this functionalization. The physical study of the energy transferts in this system will be done, relying on the strong expertise of the LAC group.
Finally, we propose to explore different shapes of the molecular crystals for photovoltaïcs, in particular, it will be interesting to prepare some 3D perovskite nanoparticles.
All these materials will be characterized optically in LAC : photoluminescence, excitation spectroscopy, pump-probe experiment and time-resolved photoluminescence. Moreover, the two PhD directors have numerous collaborations which allow to explore fully the physical properties of the material : in particular X-diffraction and photoemission experiments at SOLEIL, ab initio calculation of the band structure at INSA Rennes.
 Lee, M. M.; Teuscher, J.; Miyasaka, T.; Murakami, T. N.; Snaith, H. J. Efficient hybrid solar cells based on meso-superstructured organometal halide persovskites. Science 2012, 338, 643−647.