Two methods have been widely used in selecting host solvents and additives. (1) Host solvents usually possess a high solubility to both electron donor and acceptor molecules, whereas solvent additives have selectively higher solubility to one of the two components, typically with the acceptor. (2) Solvent additives are typically less volatile with a higher boiling point than the host solvent.60,61 A different study has been conducted to remove the residual additives by slow drying, high vacuum treatment, or by washing with a low boiling point solvent additive, such as methanol, to enhance the performance of BHJ solar cells.66 Crystal orientation, interlayer spacing, crystal size, and number of crystals depend upon the type of BHJ solar cells under study. It is observed that low vapor pressure solvent additives have a pronounced effect on enhancing crystallinity in most BHJs. In molecular systems, high crystallinity during processing obviously improves for carrier mobility and strong intermolecular interaction. Venkatesan et.al.17 compared the effects of several additives on the morphology of the active layer. Results showed that CN and DIO additives gave an optimal morphology, which helped to increase the overall efficiency of BHJ solar cells. Charge transport and bimolecular recombination dynamics were correlated with nanomorphology in polymer solar cells. Domain purity and domain size affect the charge transport and recombination dynamics.67,68 Different characterizing tools have been used for insight study of nanoscale morphology. Atomic force microscopy, Kelvin probe force microscopy, transmission electron microscopy, energy field transmission electron microscopy (EFTEM), x-ray diffraction, soft x-ray scattering, grazing incidence wide-angle x-ray scattering, and selected area electron diffraction are basic characterizing tools for morphology study at the nanoscale range.