Designed structure of bilayer TiO2–Nb2O5 photoanode for increasing the performance of dye-sensitized solar cells

Abstract

Here, we investigate the effect of crystalline structure and design configuration of photoanode semiconductor on physical properties and electron transport parameters of dye-sensitized solar cells based on niobium pentoxide (Nb2O5) composition. At the first step, the effect of calcination on structural properties of Nb2O5 has been studied. Phase transformation from mixed monoclinic/orthorhombic to pure monoclinic phase has been observed. The performance of cells is then investigated for different designs of photoanode, including pure Nb2O5, pure TiO2 and bilayer structure composed of TiO2/calcined Nb2O5. The highest performance belonged to the cell prepared bilayer photoanode. Bilayer structure facilitated charge extraction which leads to the drastically improvement of photoconversion efficiency. Remarkable increase in JSC is reported comparing to cells without TiO2 layer, from about 0.08 to around 5.7 mA cm−2, leading to conversion efficiency as high as 1.48% in the best cell. Results of dye loading measurement and impedance spectroscopy analysis revealed that this higher photocurrent is attributed to both more injected electrons from dye to photoanode and higher electron lifetime. Furthermore, inhibition of electron back-transfer from the composite layer to the electrolyte as well as low recombination resistance plays critical roles in such dramatically photoconversion efficiency.