Investigation of the effect of acid and base treatment of the photoanode on the photovoltaic parameters of Zn2SnO4-based DSSCs

We have investigated the influence of acid and base treatment of the Zn2SnO4-based photoanode on the photovoltaic performance of dye-sensitized solar cells (DSSCs). The results clearly showed that the acid treatment not only could not improve the photovoltaic performance of the fabricated DSSCs but also remarkably decreased their open circuit voltage and short current density which may be attributed to the increase in the number of the surface traps. Conversely, NaOH-treatment of the photoanodes increased the power conversion efficiency of DSSCs by about 93% relative to the untreated photoanode. Electrochemical impedance spectroscopy confirmed that the base treatment reduces the charge recombination centers on the surface of the photoanode and then facilitates charge transport. Furthermore, the significant increase in the optical absorption of the NaOH-treated photoanode indicates that the base treatment apparently increases the amount of adsorbed dye molecules on the surface of the photoanodes which can be attributed to the increase in the basicity of the photoanode surface.