Poly(3-hexylthiophene) (P3HT) and Phenyl-C61-Butyric Acid Methyl Ester (PC61BM) Based Bulk Heterojunction Solar Cells Containing Silica and Titanium Dioxide Nanorods: Molecular Dynamics Simulations

Molecular dynamics simulations are used to demonstrate the effects of introducing anisotropically-shaped silica (SiO2) and titanium dioxide (TiO2) nanoparticles on the morphology of poly(3-hexyl-thiophene) (P3HT)-phenyl-C61-butyric acid methyl ester (PC61BM) bulk heterojunction (BHJ) solar cells. The morphological compatibility and structure formation upon introduction of nanorods to the mixture of P3HT and PCBM are systematically studied by calculating several parameters that are known to influence the performance of BHJ. The anisotropically-shaped nanorods self-assemble into a variety of macroscopic structures, depending on the aspect ratio, and alter the phase morphology of PCBM. Several morphological properties such as domain size, crystallinity of the polymer phase and surface area of contact between P3HT and PCBM are found to be influenced by the presence of these nanorods. At low aspect ratios of the nanorods, the nanorod-PCBM clusters formed are kinetically-trapped and heavily branched, resulting in lower P3HT domain size and crystallinity. As the aspect ratio increases, the nanorods align parallel to each other and form two-dimensional sheet-like structures with PCBM. The P3HT crystallinity near the surface of longer nanorods were found to be higher. These changes in the morphological properties of the bulk heterojunction can be used as a benchmark to study the ternary blend solar cells with enhanced power conversion efficiency.