Zinc oxide-based dye-sensitized solar cells with a ruthenium dye containing an alkyl bithiophene group

An improved light-harvesting ruthenium dye with an alkyl bithiophene group, designated as CYC-B1, is employed as the photosensitizer for a zinc oxide (ZnO)-based dye-sensitized solar cell (DSSC). ZnO films with N3 and CYC-B1 dyes exhibit different surface appearances. Interestingly, the ZnO nanocrystal electrode surface with CYC-B1 dye is found to be almost free from Zn 2+ /dye-agglomerations, usually observed in the case of other commercial ruthenium dyes for such an electrode surface, e.g., N3 dye. Owing to this favorable effect of the CYC-B1 dye, the DSSC with a ZnO film (designated as ZN20) sensitized with this dye exhibited an average efficiency ( η ) of 4.85 ± 0.03%, which is about 94% higher than the η of the cell with N3 dye (2.50 ± 0.12%). The enhancements of the cell with CYC-B1 dye are explained by analyzing the electrochemical impedance spectra (EIS) and laser-induced photocurrent transients. Further, polymethylmethacrylate (PMMA) spheres with uniform sizes of ca. 300 nm are synthesized and incorporated to template the ZN20 film (designated as PMMA-ZN20); this PMMA-ZN20 film is used as the scattering layer and it is coated on the underlayer ZN20 film to make the photoanode film (ZN20/PMMA-ZN20) of a DSSC. The thus fabricated DSSC shows an η of 5.40 ± 0.03%.