Low band gap dyes based on 2-styryl-5-phenylazo-pyrrole: Synthesis and application for efficient dye-sensitized solar cells

A new series of low band gap dyes, C1, C2 and S, based on 2-styryl-5-phenylazo-pyrrole was synthesized. These dyes contain one carboxy, two carboxy and one sulfonic acid anchoring groups, respectively. They were soluble in common organic solvents, showed long-wavelength absorption maximum at ∼620 nm and optical band gap of 1.66–1.68 eV. The photophysical and electrochemical properties of these dyes were investigated and found to be suitable as photosensitizers for dye sensitized solar cells (DSSCs). The quasi solid state DSSCs with dye S showed a maximum monochromatic incident photon to current efficiency (IPCE) of 78% and an overall power conversion efficiency (PCE) of 4.17% under illumination intensity of 100 mW cm−2 (1.5 AM), which is higher than the other dyes (3.26% for C2 and 2.59% for C1). Even though dye S contains one sulfonic acid anchoring group, the higher PCE for the DSSCs based on this dye has been attributed to the higher dye loading at the TiO2 surface and enhanced electron lifetime in the device, as indicated by absorption spectra and electrochemical impedance spectra measurements. Finally, by increasing the molecular weight of poly(ethylene oxide) (PEO) in electrolyte, the PCE also increases up to 4.8% for the electrolyte with PEO molecular weight of 2.0 × 106. This improvement has been attributed to the enhancement in iodide ions diffusion due to the increase in free volume of polymer gel electrolyte.

A new series of low band gap dyes, C1, C2 and S, was synthesized. The quasi solid state DSSCs with dye S showed an overall power conversion efficiency (PCE) of 4.17% which is higher than the other dyes (3.26% for C2 and 2.59% for C1). By increasing the molecular weight of poly(ethylene oxide) in electrolyte, the PCE of the DSSC based on S increased up to 4.8%.Figure optionsDownload as PowerPoint slideResearch highlights▶ A new series of low band gap photosensitizers for dye-sensitized solar cells (DSSCs). ▶ New dyes based on 2-styryl-5-phenylazo-pyrrole. ▶ Power conversion efficiency of 4.17% for dye S which contains sulfonic acid anchoring group. ▶ Power conversion efficiency of 4.8% for dye S by increasing the molecular weight of PEO in electrolyte.