POSS-Enhanced Phase Separation in Air-Processed P3HT:PCBM Bulk Heterojunction Photovoltaic Systems

Nanoparticles have been shown in some cases to improve phase separation and morphology in bulk heterojunction organic photovoltaic cells. In this study, the effect of incorporation of polyhedral oligomeric silsesquioxane (POSS) molecules of different structures in air processed poly(3-hexylthiophene-2,5-diyl) (P3HT) and [6,6] phenyl C-61 butyric acid methyl ester (PCBM) films and photovoltaic cells was evaluated. Morphology and composition of the nanoscalephase-separated domains were determined via conductive atomic force microscopy in conjunction with nanomechanical mapping and Raman imaging. UV-vis and fluorescence spectroscopy analysis of the films was performed at different stages of the process and with different levels of solvent vapor and thermal annealing. It was found that POSS molecules of selected structures provided enhancement in morphology control in films, translating to improvements in fill factor and power conversion efficiency of laboratory-scale OPV cells. The findings indicate the potential for further improvements in solar cell performance with specifically tailored POSS/polymer phase separated systems.