Shi-Jhang Wu

Efficient and stable plastic dye-sensitized solar cells based on a high light-harvesting ruthenium sensitizer

A high light-harvesting ability heteroleptic ruthenium complex dye, SJW-E1, was examined as a sensitizer for the plastic dye-sensitized solar cells (DSSCs) constructed by a low-temperature electrode preparation method using binder-free TiO2 paste and an ITO-PEN substrate. The effects of a TiOxbuffer layer, electrolyte composition and co-adsorbents on the cell performance as well as the cell long-term stability were investigated. The TiOxbuffer layer has not only enhanced the adhesion between TiO2 thin film and the ITO/PEN substrate but also reduced the electron recombination, resulting in the improvement of the fill factor (FF) and therefore the photovoltaic performance of the solar cells. The optimized solar cell based on SJW-E1dye showed an efficiency of 6.31%. Furthermore, the plastic DSSCs based on the SJW-E1 dye shows a better cell stability compared to that based on N719dye after a full sunlight soaking (at ca. 50 °C) for 500 h. These results demonstrated that the flexible DSSCs based on the high light-harvesting, well-functionalized heteroleptic ruthenium dye could achieve both high performance and good stability.

Heteroleptic ruthenium antenna-dye for high-voltage dye-sensitized solar cells

A new ruthenium photosensitizer, coded CYC-B7, incorporating a bithienyl-carbazole antenna ligand was designed and prepared for improving the open-circuit voltage (Voc) of a dye-sensitized solar cell (DSC) device. This new sensitizer displays the low energy MLCT transition band centered at 551 nm with a high molar absorption coefficient of 2.19 × 104 M−1 cm−1. In addition, a simple approach to reduce the aggregation of bulky ruthenium dyes assembled onto the surface of TiO2 film is demonstrated. The cell based on this new heteroleptic ruthenium dye provides a high Voc of 788 mV and an overall conversion efficiency (η) of 8.96%. The functionality of carbazole in CYC-B7 resulting in the increases of the Voc value of the corresponding device is verified by comparing with the performance of the DSC sensitized with a structurally similar dye without carbazole.

Structural design of ruthenium sensitizer compatible with cobalt electrolyte for a dye-sensitized solar cell

Two heteroleptic ruthenium complexes, SJW-B18 and CYC-B11H, with four alkyl groups and two alkyl groups, respectively, on the terminal of their ancillary ligand were prepared. These two complexes have a similar absorption profile, energy level and orbital distribution of the frontier orbitals. Therefore, they are good model compounds to explore the effect of the molecular structure of a ruthenium sensitizer on their photovoltaic performance, especially when cobalt electrolyte was used in assembling the device. When I−/I3− electrolyte was employed, the dye-sensitized solar cell based on SJW-B18 and CYC-B11H sensitizers achieved similar power conversion efficiencies of 9.54% and 9.64%, respectively, because the two dyes have similar optical and electronic properties. Nevertheless, when Co(II)/(III) electrolyte was used, the SJW-B18 sensitized device has a higher efficiency (7.30%) than the CYC-B11H-based cell (6.65%), mainly in higher open-circuit voltage (0.829 V vs. 0.784 V). Electrochemical impedance and intensity modulated photocurrent/photovoltage spectroscopic data reveal that the SJW-B18 dyed titanium dioxide (TiO2) anode has better surface protection compared to the CYC-B11H adsorbed TiO2 film. The physical insulation of the TiO2 surface with the four alkyl groups on the SJW-B18 dye can reduce the charge recombination between the electron on TiO2 and Co(III) to increase the open circuit voltage, and the power conversion efficiency of the device. These results provide a new strategy for designing ruthenium sensitizers which are compatible with a cobalt-based electrolyte.