Enhanced dye-sensitized solar cells performance of ZnO nanorod arrays grown by low-temperature hydrothermal reaction

Abstract

SUMMARY Well-aligned zinc oxide (ZnO) nanorod arrays were formed on indium tin oxide (ITO)/glass substrates via a low-temperature hydrothermal growth of a sol–gel-derived seed layer. The seed layer was heat treated at 300 °C for 10 min prior to the hydrothermal growth using optimized conditions from our previous work to form well-aligned ZnO nanorod arrays. Hydrothermal growth time was varied for 4, 8, 12 and 24 h. Flat-top hexagonal ZnO nanorod arrays were obtained, and the length of the ZnO nanorods formed increased from approximately 150 nm after 4 h to approximately 2 µm after 24 h using a single reactive bath. X-ray diffraction patterns showed predominant ZnO peak at (002) plane for all the samples. Photoluminescence spectra of the ZnO nanorod arrays showed peaks at ultra-violet and green region, which indicated good crystalline crystal formation containing oxygen-related defects. Raman scattering results obtained showed strong band at 438 cm−1 that correlated to E2 non-polar hexagonal wurtzite phase. Dye-sensitized solar cells (DSSC) based on the well-aligned ZnO nanorod arrays were fabricated. The maximum conversion efficiency of 0.22% was achieved for the nanorods formed after a prolonged hydrothermal time of 24 h. The conversion efficiency of the DSSC increased with hydrothermal exposure time as longer ZnO nanorods provided larger surface for dye adsorption to generate more electrons. Improved crystallinity of the ZnO nanorods provided at prolonged hydrothermal time also contributed to the higher conversion efficiency as the electron transportation was enhanced. Copyright © 2013 John Wiley & Sons, Ltd.