Abstract :
[en] The main objective of this master thesis is to optimize CH3NH3PbI3-like perovskite coatings (thickness, cell architecture, chloride doping) in order to prepare photovoltaic cells with conversion efficiencies higher than 10%. The 3D structuring of porous perovskite films is also studied in order to highlight the effect of this structuration on the efficiency of the corresponding cells and on the optical properties of the films in terms of semi-transparency and/or coloration, in comparison with the dense perovskite films usually used. This work is therefore divided into two parts devoted to perovskite dense films and porous films, respectively. The perovskite films are prepared through 1-step process (deposition of a solution containing the Pb precursor and CH3NH3I) or 2-steps process (deposition of the Pb precursor followed by its conversion by CH3NH3I or CH3NH3Cl). For the preparation of the perovskite porous films, polystyrene beads are used as a structuring agent.
The first part of the work devoted to the optimization of dense films shows that the most homogeneous 1-step non-doped CH3NH3PbI3 perovskite films are obtained with DMSO as a solvent, the duration of the heat treatment at 100°C has no impact on the morphology of the films and the anti-solvent smoothing with sec-butanol allows for further improvement of the films homogeneity and coverage. However, PV efficiencies of the corresponding cells are low and a decrease is even observed with the sec-butanol smoothing due to a lack of adherence of the films. The 1-step doped CH3NH3PbI3-xClx perovskite films are therefore investigated to improve charge transfer and to reduce recombination. The obtained films, despite poor coverage and a lack of uniformity, lead to an increase of the efficiencies from 2.1% to 4.0% in direct scanning direction thanks to the doping. The 2-steps non-doped CH3NH3PbI3 perovskite films are also studied. The conversion of a PbI2 film by dipping in a CH3NH3I solution gives the best results. For the 2-steps doped CH3NH3PbI3-xClx perovskite films, the best results are obtained by converting a PbI2 film by a solution of both CH3NH3I:CH3NH3Cl and an efficiency of 12.1% is reached for our best cell. The use of the non-doped CH3NH3PbI3 perovskite in combination with a TiO2 mesoporous film is also considered to improve the PV efficiency of the cells, reaching 11.0% for our best cell. The addition of a TiO2 mesoporous film or the perovskite doping is therefore required to achieve conversion efficiencies higher than 10%.
In the second part of the work devoted to the 3D structuring of porous perovskite films, five polystyrene beads diameters are studied: 300 nm, 540 nm, 810 nm, 1.0 μm and 2.1 μm, to highlight the effect of the beads diameter on the optical properties of the films and on the PV efficiency of the corresponding cells. The 1-step process gives the best results. PbI2/CH3NH3I 0.7 M and PbCl2/CH3NH3I 1.0 M solutions in DMSO lead to the most covering, homogeneous and overlayer-free porous films of 1-step non-doped CH3NH3PbI3 and doped CH3NH3PbI3-xClx perovskite, respectively. The efficiency of the corresponding cells increases with the beads diameter. A significant improvement in the PV conversion efficiency is observed thanks to the 3D structuring for the non-doped CH3NH3PbI3 perovskite films. In addition, CH3NH3PbI3-PS810, CH3NH3PbI3-PS1000, CH3NH3PbI3-PS2100 and CH3NH3PbI3-xClx-PS2100 porous films are obviously colored, which is very interesting for building integration of these PV cells (BIPV).
