Perforated ZnO Nanoflakes via Hydrothermal Routes for Dye Sensitized Solar Cells (DSSC) Applications

Abstract

Highly porous flakes-like ZnO nanostructures are successfully synthesized by hydrothermal route using zinc acetate as precursor and DI water as a solvent. HMT and ammonia were used as additive and surfactant, respectively. The two different sets of ZnO nanostructures are synthesized by varying ammonia solution amount (Z1-H and Z2-H). The structural, morphological and optical properties of as-prepared powder were studied by different characterization techniques. The structural analysis of synthesized powder shows the formation of hexagonal wurtzite ZnO. The optical absorption peak of synthesized ZnO exhibited blue shift as compared to the bulk ZnO. Morphological study showed formation of highly perforated flakes like morphology with different thickness revealing their high surface area. The efficiency characteristics for DSSCs were measured under simulated sunlight illumination of 100 mW/cm² intensity. It was found that the best results of DSSCs were observed with power conversion efficiency of 2.08% and 2.81% for Z1-H and Z2-H as photoanodes, respectively, which was significantly 3 to 4 times higher than the commercial ZnO. The efficiency enhancement can be explained by increasing of dye adsorption on perforated ZnO flakes due to enhancement of the active surface area of photoanode. The charge recombination behavior of cells was inspected by electrochemical impedance spectra (EIS), and the results showed that Z2-H based cell with lower thickness of nanoflakes have the lowest transfer resistance and the longest electron lifetime, which could facilitate the reduction in recombination processes and thus would promote the solar-cell performance.