Electrochemical properties and trap states of TiO2 nanoparticles modified by doping with graphene and used as counter electrodes for dye-sensitized solar cell applications

Abstract

The electrochemical properties and trap states of TiO2 nanoparticles that are modified by doping with graphene (Gr) and used as counter electrodes (CEs) for dye-sensitized solar cell (DSSC) applications are studied. This research demonstrates the operation of a DSSC that features a TiO2 CE, with or without the addition of Gr. TiO2 nanoparticles are used as the CE for a DSSC to determine their specific properties and to determine the effect of trap states in TiO2 on the photovoltaic performance. The photovoltaic performance for DSSCs is affected by the addition of Gr. In a CE that uses TiO2, the long-lifetime and short-lifetime carrier traps render the charge transfer behavior more complex. The existence of trap states induces photovoltaic instability. The incorporation of Gr leads to an increase in the power conversion efficiency and the photovoltaic stability for a DSSC, because of the change in the over-potential at the TiO2 CE/electrolyte interface and the dominance of the long-lifetime hole detrapping that is related to the formation of the Gr percolation paths in a TiO2 CE that is doped with Gr.