High‐Gain Graphene‐Titanium Oxide Photoconductor Made from Inkjet Printable Ionic Solution

As an alternative to such layer-by-layer assembled fi lms, which require multiple dipping cycles in different solutions, it is interesting to consider whether an optically transparent and electrically conducting matrix comprising of homogeneously dispersed TiO 2 and graphene can be synthesized. Ideally this composite blend would be derived from a homogenized mixture that acts as a precursor source and that can be spin-coated or inkjet-printed onto any substrate to be thermally sintered into a transparent conductor or light-harvesting photoconductor fi lm. Here, we show that a conventional sol-gel chemistry approach used previously for the formation of graphene-silica composites [ 6 ] is not applicable to GO-TiO 2 systems. Instead, we report a strategy based on blending GO sheets with a titanium hydroxide-based ionic salt to produce a chemically tunable graphene-TiO 2 composite, which can be used as a printable photodetector. The fabricated structure exploits the desirable charge injection and separation properties at dispersed heterojunctions, and thus opens a widely applicable fabrication strategy for graphene-based composites in photoconductors, sensors, and photovoltaics. Looking at their chemical structure, GO sheets are wellsuited to blending with titanium alkoxide precursors in solgel synthesis because of their water solubility and hydrogenbonding ability (Schematic 1 a). GO sheets are composed of planar, graphene-like aromatic domains and the basal planes and edges are decorated by hydroxyl, epoxy, ether, or carboxylic groups. [ 7 ] These hydroxyl functionalities in GO can participate in oxoor hydroxobridges with metal centers. The formation of titanium oxide in sol-gel synthesis involves interconnecting