ABSTRACT
Donor-acceptor interfacial microstructures and fast ambipolar charge transport are pivotal in determining the device performance of inorganic-organic hybrid photovoltaics. Here, we report on a series of one-dimensional coaxial p-n junction core-shell nanohybrids formed by direct side-on attachment of carboxylated poly(3-alkylthiophene)s onto single-crystalline ZnO nanowires. The diameter of pristine ZnO nanowires is â¼30 nm, and the conjugated polymer forms a 2-10 nm shell around each nanowire. Spectroscopic studies on the resulting core-shell hybrid nanowires show an elongated conjugation length of the poly(3-alkylthiophene) backbone and fast electron transfer via ordered donor-acceptor interfaces. Hybrid nanowires in suspensions spontaneously undergo phase transitions from isotropic to nematic liquid crystalline phases via a biphasic region with increasing concentration. The unique liquid crystalline elasticity of nanohybrids results in large-area monodomain structures of aligned hybrid nanowires under simple shear flow, which are maintained in the dried film used for device fabrication. These methodologies provide a mechanism for controlling donor-acceptor interfaces and exploiting lyotropic liquid crystallinity for solution-based processing of large-area alignment of photovoltaic elements with anisotropic charge transport for hybrid photovoltaic devices.
ABSTRACT
We report on a series of experiments on large-area ordered patterns of graphene oxide on solid substrates deposited from aqueous dispersions by directed drop evaporation. The aqueous dispersion of graphene oxide exhibits phase transitions from isotropic to liquid crystalline nematic phases via a biphasic region with increasing concentration. In the single nematic phase, schlieren textures accompanied by oriented bands are frequent. Drying of drops in each phase results in deposition covering the whole drop base. The dynamic process of drop drying is analyzed based on the weight loss, radius change, and texture change over time. It is found that the radial bands develop in the nematic drops in the vicinity of the receding of the contact line and subsequently transform into birefringent stripes after drying. Study into the structure and morphology of the stripes reveals anisotropic wrinkling of graphene oxide sheets. The nature of stripe orientation is strongly dependent on the local nematic order at the dewetting water front. Various macroscopic patterns with different stripe orientations including radial spokes, spider webs, and parallel stripes have been generated by tuning the nematic order of drops.
