Stable Surfactant-Free Colloidal Dispersions for Organic Photovoltaic Solar Cells
Résumé
In this study, we will use the solvent shifting technique (or "Ouzo Method") in order to prepare surfactant-free stable colloidal dispersions of poly(3-hexylthiophene) (P3HT) and/or [6-6]-Phenyl-C61-butyric acid methyl ester (PCBM) nano-particles in non-toxic solvents. Depending on several parameters (type of solvents, initial concentration, ratio good/bad solvent, pH, molecular weight), it is possible to tune the size and crystallinity of the particles. DLS and AFM were used to determine their size and shape: sphere with diameter between 50 and 150 nm were detected. The resulting colloidal dispersion can be made of both kinds of particles, donor and acceptor, or the donor particles dispersed in an acceptor solution. From this last dispersion, it would be possible to have the ideal morphology for organic solar cells: donor nano-particles in an acceptor matrix. The ability of these colloidal dispersions to form thin films was investigated using several coating techniques: Dr. Blading, ultrasonic spray and standard spray coating. The morphology of the resulting films were analysed by AFM and SEM. Controlling the temperature deposition process enables to tune the film morphology from stacked nanoparticles to rough melted matrix. In some cases, interesting P3HT porous nanostructure was identify useful for the back infiltration of PCBM, in order to develop an ideal bulk heterojunction with well defined P3HT and PCBM domains and vertical phase segregation. The photovoltaic properties of these kinds of layers will be presented.