2-Diphenylaminothiophene as the donor of porphyrin sensitizers for dye-sensitized solar cells
Four novel D–π–A porphyrin dyes (YQ1–YQ4) with 2-diphenylaminothiophene attached at the meso-position as the electron donor have been synthesized and used as the sensitizers for dye sensitized solar cells (DSSCs). 4-Ethynylbenzoic acid and 2-cyanoacrylic acid were incorporated as the anchoring moieties in YQ1, and YQ2–YQ4, respectively. Due to the extended conjugation size, the absorption spectra of YQ2–YQ4 showed Soret band maxima in the range of 447–468 nm, which is red shifted as compared to that of 446 nm for YQ1. Furthermore, in comparison with most reported porphyrin dyes with similar structures, YQ1–YQ4 demonstrate obviously red-shifted absorption maxima and broadened Soret bands, indicating that these porphyrin dyes may be developed as promising DSSC sensitizers. The electrochemical studies and DFT calculations indicated that all the four dyes were capable of serving as DSSC sensitizers. Thus, DSSCs were fabricated based on these dyes. The cells based on YQ4 showed the power conversion efficiency of 5.00%, which is higher than those of 4.23% and 4.38% for YQ2 and YQ3, respectively. This observation may be attributed to the suppression of the dye aggregation by the hexyl group attached to the thienyl ring of YQ4. On the other hand, YQ2–YQ4 demonstrated lower efficiencies compared with YQ1, which may be ascribed to the floppy structures of the cyanoacrylic acid-based porphyrins that provide free space for charge recombination. As a result, the DSSCs based on YQ1 exhibited the highest efficiency of 6.01%. This work demonstrates that the introduction of 2-diphenylaminothiophene into a porphyrin framework can obviously red-shift and broaden the absorption bands of the porphyrin dyes, resulting in high solar cell efficiencies. Hence, the introduction of 2-diphenylaminothiophene as the electron donor may be promising for the design of efficient porphyrin-based DSSC sensitizers.