Structural effect of Low-dimensional carbon nanostructures on Long-term stability of dye sensitized solar cells

Abstract

A major challenge in upscaling and commercializing dye-sensitized solar cells (DSSC) is to simultaneously rely on a robust photoconversion efficiency (PCE) along with long-term device stability. Two-dimensional (2D) nanocarbon materials are known to improve the PCE and stability of devices made of hybrid nanocomposite photoanodes. However, there is inadequate knowledge on how the morphology of 2D nanocarbon materials plays an important role in improving photovoltaic (PV) performance and stability. Here we report the comparative effect on the PV performance and the long-term stability of DSSCs made of optimal loadings of few-layer graphene (FLG) flakes and graphene nanoribbons (GNR) into the mesoporous TiO2 active layer. DSSCs were fabricated by using standard nanocrystalline TiO2, GNR-TiO2 and FLG-TiO2 hybrid mesoporous films as anodes and subjected to continuous visible light irradiation to monitor their long-term stability. Results show that the optimized incorporation of GNR (0.005 wt%) and FLG (0.010 wt%) in the mesoporous TiO2 active layer enhances the PCE by 34% and 21% compared to pristine TiO2, respectively. Moreover, the operational stability of hybrid devices shows a 51.6% (for GNR-TiO2) and a 10% (for FLG-TiO2) sustained higher PCE than the device based on bare TiO2, after 273 h of continuous one sunlight soaking. The electrochemical impedance spectroscopy (EIS) and transient photovoltage decay were studied to investigate how GNR strikingly reduces degradation of device performance as compared to its counterpart FLG-TiO2 and TiO2 based cells. This significant enhancement can be attributed to the structural modifications induced by GNR within the TiO2 photoanode, which improves the electron lifetime and reduces non-radiative carrier recombination.