Novel zinc porphyrin sensitizers for dye-sensitized solar cells: Synthesis and spectral, electrochemical, and photovoltaic properties

Two donor–π-spacer–acceptor porphyrin dyes were synthesized for use in dye-sensitized solar cells. The dyes comprised the same donor (porphyrin derivative) consisting of 3,4,5-trimethoxybenzaldehyde and acceptor/anchoring group (carboxyl group) but varying π-spacer consisting of a Schiff base structure. Each of the dyes displayed different adsorption behavior and coverage on the TiO2 surface. The porphyrin dyes PZnBIACOOH studied in this work exhibit red-shifted and broadened electronic spectra respect to the reference PZnCOOH as expected. By the introduction of Schiff base unit at the meso positions, the energy level of Eox (excited-state oxidation potentials) is significantly shifted to the positive compared with the reference PZnCOOH, indicating a decreased HOMO–LUMO gap. The highest power conversion efficiency of the two dyes based on DSSCs reached 1.75% under AM 1.5 G irradiation.