SAMOS

In the course of this work, in a first top-down approach, we studied the realization of evaporated multilayer solar cells based on organic materials: pentacene and PTCDI-C5. This approach was developed during Y. Dufil in J.M. Nunzi's group at Queen's University. We used it to build and characterize single junction bilayer cells. These cells served as a reference model for our study, demonstrating capabilities in line with the literature. We then produced and characterized multijunction bilayer cells. A quick study of the behavior of a nanometer-thick layer of silver was used to deposit the recombination layer of these cells. Unfortunately, all the multi-junction cells exhibited characteristics similar to those of a single-junction cell. In particular, the expected increase in open circuit voltage was not observed. This seemed to indicate the presence of a short-circuit within the additional junctions, but although we tried to demonstrate this by scanning electron microscopy after FIB erosion at our partners at UCT Prague, we were unable to observe any short-circuit.

We then set about the realization of self-assembled monolayers on silicon with the aim of developing active donor-acceptor layers and stacking them using the bottom-up approach (Fig. 1).

After studying the silane and phosphonic acid anchor groups, we investigated the realization of (3-Trimethoxysilylpropyl) diethylenetriamine (DETAS) SAMs on silicon as an anchor layer for active molecules (Fig. 4a). We demonstrated that relative humidity plays a key role in the formation of DETAS SAMs with a non-polar solvent such as toluene and leads to multilayers by micellar deposition when it reaches 40% and above. The observations suggest that to obtain good quality DETAS SAMs, a minimum DETAS concentration of 2.5×10-2 M and a long chain of alcoholic solvent are required. The kinetics show immediate adsorption of the molecule at the very first moment of the SAM formation process, which is rare for organosilane grafting. The thickness remains almost constant for more than 30 minutes before increasing with the organization of the molecule by hydrogen bonds between the primary (NH2) and secondary (NH) amine functions thus helping the organization of the SAM. This was highlighted by infrared spectroscopy ATR-FTIR carried out at the University of Toulon with P. Carrière of MAPIEM. This work has been recently published.

We then used this SAM as an adhesion layer for the grafting of a photoactive molecule perylene tetracarboxylic dianhydride (PTCDA) (Figs. 4b and 4c).

AFM, ellipsometry and Raman spectroscopy techniques were used to characterize the surface after PTCDA grafting.