Effect of annealing temperatures on performance of DSSCs fabricated using Ag or Pd@C@ZnO composites as photoanode materials

ZnO nanorods have been synthesized with microwave treatment and co-precipitation method. Different concentrations of Ag@C and Pd@C nanospheres prepared by hydrothermal method were loaded onto ZnO nanorods. The sample obtained was characterized by x-ray diffraction (XRD), UV–vis reflectance spectroscopy (DRS), scanning electron microscopy (SEM), and Energy dispersive X-ray spectroscopy (EDX). The metal content did not change the peak position deducing that prepared materials were of high purity. Different types of cells were prepared to check the effect of noble metal content on the optical property on ZnO and annealed at different temperatures. The cells were tested in a conventional architecture sing Pt counter electrode and I^-/I^-₃ electrolyte. The dye sensitized solar cells (DSSCs) based on Ag@C-ZnO photoanode including 50 mg Ag annealed at 500 °C was found to be more efficient among all DSSs with an efficiency of 3.60% and a current density of 7.87 mA/cm² with a fill factor of 59.3%. While DSSC based on Pd@C-ZnO photoanode including 50 mg Pd with the same conditions was observed to possess 1.93% efficiency with current density 6.01 mA/cm² and fill factor of 42.9%. The enhancement in ZnO efficiency is attributed to the reduction in electron hole recombination and increase in photo-generated e^-/h⁺ due to presence of noble metals and valonea.