A Step Toward Efficient Panchromatic Multi-Chromophoric Sensitizers for Dye Sensitized Solar Cells

Panchromatic dyes with absorption profiles extending into the near-infrared are of interest to researchers in the field of dye sensitized solar cells (DSSCs), as they offer potential access to a wide energy range of photons necessary to enhance solar to electric power conversion efficiencies (PCEs). In this report, a porphyrin with a Soret band absorbing at high energy is combined with a squaraine absorbing at low energy via an acetylene linker to form a bichromophoric sensitizer with molar extinctions on the order of 105 M–1 cm–1 and an incident photon-to-current efficiency (IPCE) onset of ∼850 nm. Various bulky substituents were installed on both the porphyrin and squaraine moieties, and conjugation was increased with π-bridge spacers to achieve a PCE of 7.6%, which is up to 15% higher than a comparable squaraine-only dye. For the most part, charge injection dynamics indicate slower charge injection rates and lower injection quantum yields for these bichromophoric sensitizers compared to nonporphyrin squaraine-based DSSC sensitizers. Nevertheless, higher PCE was observed for most porphyrin-containing dyes due largely to increased panchromaticity.