A Molecular Engineering Strategy of Phenylamine-Based Zinc-Porphyrin Dyes for Dye-Sensitized Solar Cells: Synthesis, Characteristics, and Structure–Performance Relationships

The molecular engineering of phenylamine- and phenothiazine-based porphyrin dyes is an advisable strategy for high-efficiency dye-sensitized solar cells (DSSC). Herein, we incorporated two and three phenothiazine units into the triphenylamine donor (D) unit of porphyrin dye (T-1) to replace the benzene units, resulting in two novel porphyrin dyes, T-3 and T-4. UV–vis absorption studies revealed that the molar extinction coefficients (ε) on TiO2 films of T-3 and T-4 were significantly higher than T-1, mainly owing to the increased loaded amount. Hence, the T-3- and T-4-devices exhibit higher IPCE and Jsc values. Furthermore, transient PL measurements and electrochemical impedance spectroscopy (EIS) results demonstrate that the electron injection efficiency (ηinj) and electron lifetime (τ) of the T-3-device were the highest. Thus, the T-3-device achieved the highest power conversion efficiency (PCE) of 8.02% (N719, 8.45%) with Voc = 670 mV, Jsc = 16.84 mA cm–2, and FF = 70.02%. Meanwhile, the theoretical calculation studies suggest the smaller dihedral angle between the D unit and porphyrin macrocycle of T-3, leading to a favorable intramolecular charge transfer (ICT) process (t = 1.831, qct = 0.922) compared to that of T-4. These results demonstrate that introducing a different number of phenothiazine units to replace the benzene units of triphenylamine in suitable positions can serve as an effective strategy for developing efficient DSSC.