<br/>Photo-electrodes are the heart of photovoltaic and photocatalytic technologies. The traditional photoanode structure is composed of a transparent conductor (TC) on glass, i.e. fluorine or indium-doped tin oxides (FTO, ITO), coated with a n-type semiconductor, that allows for the conversion of photons into electrons. Graphene is a promising TC alternative, with larger flexibility and optical transmittance, that can be synthesized from renewable sources. In recent years, graphene has been largely explored as an additive in photoanodes, but rarely has it been applied to fully replace the functionality of FTO or ITO. We explore the application of high quality graphene films obtained by chemical vapor deposition as TC in tin oxide-free photoanodes using ZnO as the n-type semiconductor. In our work, we explore different methods for the deposition of ZnO on graphene and the effects on their performance as photoanode materials. By simple slip-casting of ZnO nanoparticles, we have shown that graphene DSSCs render similar efficiency but faster rates of charge recombination in comparison to FTO cells, due to graphene's electro-catalytic activity towards triiodide reduction. We are currently exploring the technique of electrodeposition to accurately tune the morphology and crystal structure of the ZnO nanostructures grown on graphene. This <i>in-situ</i> deposition of ZnO nanostructures is expected to result in more efficient charge transfer from ZnO to graphene and provide a passivating effect to prevent shunt current leakage. Electrodeposition has the advantage of lower processing temperatures and shorter deposition times in comparison to hydrothermal and chemical vapor deposition, and is very versatile, allowing the growth of a broad range of nanostructures, including hierarchical structures produced in one-pot processes. We prepare different morphologies of ZnO on graphene and compare the charge transport within the materials and across the interfaces. The charge kinetics and resistance elements of the DSSCs are estimated from linear sweep voltammetry, electrochemical impedance spectroscopy and open-circuit voltage decay measurements, complemented with model fitting. This integral approach for photovoltaic performance evaluation provides deep understanding of the internal processes taking place in the DSSCs and traces the route to optimize graphene 3D hybrid nanomaterials for photovoltaics.

Deposition of ZnO nanostructures on graphene: Application as tin oxide-free photoanodes

253rd National Meeting (2017)

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