Role of hexyloxy groups in zinc phthalocyanines bearing sulfonic acid anchoring groups for dye-sensitized solar cells

Zinc phthalocyanine dyes bearing four sulfonic acid anchoring groups with (A-ZnPc) and without (H-ZnPc) four chloro and eight hexyloxy groups were used as sensitizers for dye-sensitized solar cells (DSSCs). The dyes were investigated in terms of their optical, electrochemical and photovoltaic properties. The presence of these groups in dye A-ZnPc resulted in both red-shifted absorption and decreased dye aggregation, which are beneficial for the improvement of device performance. In the presence of chenodeoxycholic acid (CDCA) as a coadsorbent, the DSSC based on H-ZnPc shows a power conversion efficiency (PCE) of 0.96%, which is improved by similar to 40% as compared to the device without CDCA. However, the PCE of an A-ZnPc-based device with CDCA slightly enhances from 1.15% (without CDCA) to 1.22%, indicating that the bulky hexyloxy groups with large steric hindrance can effectively suppress aggregation of the adsorbed dye. The results showed that the zinc phthalocyanine dye bearing bulky hexyloxy groups is a promising candidate to construct efficient coadsorbent-free DSSCs.