Transparent graphene–platinum nanohybrid films for counter electrodes in high efficiency dye-sensitized solar cells

Abstract

A dispersion of platinum-on-graphene was prepared essentially by a two-step process, involving uniform distribution of graphene nanoplatelets in a cosolvent of ethanol–water in the presence of a polymeric dispersant and subsequent in situ reduction of dihydrogen hexachloroplatinate to metallic platinum on the graphene surface. The process generated platinum nanoparticles (PtNPs) of ca. 4.0–10 nm in diameter on the graphene surface. The platinum-on-graphene dispersion was coated on an FTO glass to prepare a counter electrode (CE) for a dye-sensitized solar cell (DSSC). The hybrid film of platinum nanoparticles and graphene nanoplatelets (PtNP/GN) showed a transparency of 70% at 550 nm, indicating its suitability as a CE material for a rear-illuminated DSSC. The DSSC with the CE having the film of PtNP/GN exhibited a power conversion efficiency (η) of 8.00%, superior to 7.14% of the DSSC with a conventional sputtered platinum (s-Pt) CE. In the case of rear-illumination the DSSC showed an η of 7.01%, while the DSSC with the conventional s-Pt showed an η of only 2.36%. HRTEM and FE-SEM were used to observe the dispersion of the hybrid material in the solvent, UV-vis spectroscopy and cyclic voltammetry were used to characterize the films, and IPCE spectra and electrochemical impedance spectra were used to explain the photovoltaic parameters of the DSSCs.