New A3B-type naphthyl Zn(II) porphyrins as DSSC dyes: Effect of anchoring group and co-adsorption for enhanced efficiency

Abstract

Two new Zn(II) porphyrin dyes ZnNPCA and ZnNPHy bearing three naphthyl groups and one carboxyphenyl/hydroxyphenyl anchoring group in an A3B meso substitution pattern was synthesized utilizing a mixed condensation approach. The redshifted absorption bands to 427 nm as impacts on the extended conjugation with three naphthyl substituents. Similarly, the emission spectrum also exhibits a redshift than ZnTPP-COOH dye. The anodic shift was found in the reduction potential of the naphthyl dyes with the carboxylic acid anchor (ZnNPCA), facilitating the more favourable electron injection. Moreover, the naphthyl porphyrin dyes positively interacted with semiconducting TiO2, whose binding mode was further established using FT-IR. While interacting with titania, the more broadening absorption spectra exhibit strong electronic coupling and will benefit the electron injection. The high dye loading amount obtained for ZnNPCA dye was 13.1 × 10−8 mol cm2, which is more significant towards light harvesting. DSSC devices were fabricated using porphyrin-sensitized photoanodes. ZnNPCA showed better efficiency than ZnNPHy owing to higher dye loading onto the titania surface. Furthermore, the influence of co-adsorbent DCA on the photovoltaic performance of the fabricated DSSC devices was investigated. As a result, a maximum efficiency of 1.85% was achieved for ZnNPCA/DCA device. In addition, electrochemical impedance spectroscopy results revealed a higher electron lifetime (6.14 ms) for this device, supporting better suppression of back reactions.