All-Solid-State Dye-Sensitized Solar Cells Based on Push-Pull Zinc Porphyrin and Metal-Free Organic Sensitizers

Porphyrins have been designed and synthesized based on the molecular structure of YD2-oC8 for applications of dye-sensitized solar cell (DSSC) to reach PCE 13 % using cobalt-based liquid-type electrolyte. However, traditional liquid-type devices suffered from leaking of electrolyte and the best solution is to replace it with solid hole transporting materials like spiro-OMeTAD. In this lecture, I will present our recent results of all-solid-state DSSC based on a series of novel porphyrin sensitizers together with co-sensitization of porphyrins with organic dyes and/or porphyrin dimers. Extension of p-conjugation can be achieved by attaching various cyclic aromatic hydrocarbon substituents, such as anthracene, tetracene, pyrene, fluorene, and amino-substituted electron-donating groups opposite to the anchoring group of the target porphyrin. The reference porphyrin is the LD14 dye, which makes a traditional DSSC attaining PCE 9.2 % using iodine-based electrolyte. When the functional group has been inserted into the position between porphyrin core and the donor group, the efficiency of the device made of spiro-OMeTAD HTM attained PCE 4.1 %. The solid state device has the configuration FTO/TiO₂ (1.8 mm)/porphyrin/spiro (180 nm)/Ag. Another new push-pull porphyrin was designed to insert the functional group Benzothiadiazole (BTD) in the position between the porphyrin core and the anchoring group. By co-sensitization of this porphyrin with a newly designed organic dye on a TiO₂ film of 1.8 mm, the solid-state device showed a promising performance with PCE 5.5 %. Both time-resolved (TAS) and frequency-domain (EIS) techniques were applied to understand charge transport and recombination kinetics with respect to their photovoltaic performances.