Broadband light harvesting and fast charge separation in ordered self-assemblies of electron donor-acceptor-functionalized graphene oxide layers for effective solar energy conversion

Three-dimensionally (3D) ordered assemblies of GO layers functionalized with tetrakis(1-methylpyridinium-4-yl)porphyrin p-toluenesulfonate (Por), N,N′-di(2-(trimethylammonium iodide)ethylene) perylenediimide (PDI), and Zn(II) phthalocyanine tetrasulfonic acid (ZnPc) were obtained in water. Proper molar ratio is essential between the cationic dyes, Por and PDI, acting as the "glue" molecules to combine the GO layers and the anionic ZnPc, acting as dispersant of GO layers to (i) construct the 3D assemblies and (ii) the proportional absorption distribution of dye-functionalized GO assemblies. Resulting 3D structures effectively harvest the light from ultraviolet to near-infrared (NIR) regions. Dye molecules are arranged in mainly lateral order on the GO layers with partial stacking, which allows direct interactions with the π-conjugations of the GO surface in 3D architecture. Ultrafast charge separation upon the photoexcitation of the dyes at various wavelengths in the visible/NIR region was observed in these assemblies, in which ZnPc and PDI were the ultimate electron donor and acceptor, respectively. Lateral charge migration among the partially stacked dye molecules was inferred from the decay characteristics of the radical ion pair. Triggered by the charge separation processes in the 3D ordered self-assemblies, significantly higher photocurrent density in the OTE/SnO₂ electrode deposited with self-assemblies of (GO-Por-PDI-ZnPc)_n was generated compared to those deposited with only GO or dye components.