Electrodeposition of ZnO nanorods on graphene: tuning the topography for application as tin oxide-free electron transport layer

Abstract

The heterostructure of graphene and ZnO nanorods is attractive as a tin oxide-free electron transport layer for a broad variety of excitonic photovoltaic technologies. This work focuses on the effect of electrodeposition variables on morphology and performance of vertically aligned zinc oxide nanorods (ZVNRs) on graphene. This in situ growth technique has potential for fabrication of a wide variety of graphene heterostructures under mild synthesis conditions to prevent graphene damage. Large area graphene was grown by chemical vapor deposition, stacked up to four atomic layers, and transferred to glass. ZVNRs were electrodeposited on the graphene-coated glass and the topography was controlled by changing the electrodeposition parameters of the time, temperature, stirring, and seeding layers. The mechanisms controlling the cathodic electrodeposition of nanocrystals on graphene were studied by scanning electron microscopy of the ZVNRs topography. The effect of the topography of the ZVNRs on the electron generation and transport was studied for photoanode application in reference dye-sensitized solar cells. The charge transfer resistance and kinetics of the materials as photoanodes were measured with the techniques of linear sweep voltammetry, open circuit voltage decay, and electrochemical impedance spectroscopy. The optimization of ZnO growth resulted in an increase of the surface-to-volume ratio of the electrode from 10 to 250 mm−1, 60-fold increase of electron lifetime and ten-fold increase in power output. The results of this study provide fundamental understanding for designing electrodeposition processes of the hybrid ZVNR/graphene material.