Chemical structure of ZnO nanorod array on a DSSC photoanode

The main objective of the present work was to study speciation of ZnO nanorods during the photoexcited electron transfer between photosensitive dyes and the ZnO nanorod arrays on the photoanode of a dye-sensitized solar cell (DSSC) by X-ray absorption (near edge structure (XANES) and extended X-ray absorption fine structure (EXAFS)) spectroscopy. The least-square component fitted XANES spectra show that the main zinc species in the ZnO-nanorod photoanode are nanosize ZnO (88%) and Zn(OH)₂ (12%). An enhanced adsorption of the dyes N3 (C₂₆H₂₀O₁₀N ₆S₂Ru) and mercurochrome (C₂₀H ₈Br₂HgNa₂O₆) on the ZnO nanorods is found, of which 6-10% of the nanosize ZnO involve in the chemical interaction with the dyes. Their EXAFS spectra also indicate that the bond distance and coordination number of Zn-0 in the ZnO nanorods is 1.95 å (which is less than that in the ZnO seedlayer by 0.01 å) and in the range of 4.6-4.8, respectively. The efficiencies of the DSSCs containing the N3 and mercurochrome dispersed ZnO nanorods on the photoanodes are 0.33-0.92%. The relatively less J_sc (photocurrent density) of the DSSC with the N3-dispersed ZnO nanorod may be due to the formation of a N3-Zn²⁺ complex. A rapid recombination of the photoexcited electrons with I₃^- in the electrolyte of the DSSC containing the N3 dispersed ZnO nanorods is also found, which causes a reduction of its FF (fill factor) value.