Dependence of nanocrystal dimensionality on the polymer nanomorphology, anisotropic optical absorption, and carrier transport in P3HT: TiO₂ bulk heterojunctions

It is known that the nanoscale morphological organization of donors or acceptors in bulk heterojunction (BHJ) solar cells is critical to device performance and strongly affects carrier generation, transporting, and collection. This work demonstrates the dependence of nanocrystal dimensionality and organization on the polymer nanomorphology in P3HT:TiO₂ hybrid bulk heterojunctions, which were revealed using grazing-incidence X-ray diffraction (GIXRD) using a synchrotron X-ray beam and electron tomography. We further performed a multiscale molecular dynamic simulation to understand the morphological orientation of a polymer blended with TiO₂ nanoparticles (NPs) or nanorods (NRs). The correlation between polymer nanoscale morphology and the dimensionality and anisotropy of nanocrystals in P3HT:TiO₂ hybrids clearly explains the observation of different optical absorption and carrier transport behaviors in directions perpendicular or parallel to the film substrate. Our results provide crucial information toward understanding the interplay between nanocrystal dimensionality and polymer morphology in developing organic/inorganic hybrid electronic devices such as thin film transistors (TFTs) or photovoltaics (PVs).