Influence of spacer and donor groups as tetraphenylethylene or triphenylamine in asymmetric zinc phthalocyanine dyes for dye-sensitized solar cells

Based on the available literature, the carboxylic acid is a suitable electron-withdrawing group for the development of push–pull type AB3 phthalocyanines that can be used in dye-sensitized solar cell (DSSC). This study aims to assess the impact of carboxylic acid groups on solar cell energy conversion efficiency. Two types of carboxylic acid groups were selected as electron-withdrawing groups for this purpose. These groups were attached to the phthalocyanine (Pc) core either directly or via conjugated linker groups. Two novel push–pull zinc phthalocyanine dyes (GT-52 and GGC-22) containing tetraphenylethylene (TPE) or triphenylamine (TPA) substituents as electron donor groups and carboxylic acid or phenoxy carboxylic acid as anchoring groups, respectively, have been synthesized to construct DSSCs. The optical, electrochemical, and photovoltaic properties of the effect of the spacer and electron donor groups in these phthalocyanines are evaluated. Both dyes exhibit good anti-aggregation ability owing to the presence of the bulky donor groups. On the other hand, the DSSC based on GGC-22 showed a significantly higher power conversion efficiency (PCE) of 2.15% than that of GT-52 (0.26%) under AM 1.5G solar conditions. The superior performance of GGC-22 is attributed to the introduction of a phenoxy spacer, which results in a longer distance between the donor groups and the TiO2 surface compared to GT-52 without any spacer. This allows for higher dye loading, resulting in higher JSC, VOC, and PCE for GGC-22. As a result, the presence of a longer anchoring group for the donor groups is an important synthetic strategy for efficient phthalocyanine-based DSSCs.