Novel organic dyes based on diarylmethylene-bridged triphenylamine for dye-sensitized solar cells

• Organic dyes containing diarylmethylene-bridged triphenylamine are synthesized.
• The hexyl substituted thiophene attached are advantageous for light harvesting.
• Dye TTB-1 provides the highest power conversion efficiency of 4.35 %.

Three D–π–A type organic dyes, including TB-1, TTB-1 and TTB-2, which contained bridged triphenylamine (TPA) donor moieties, were synthesized and characterized for applications in dye-sensitized solar cells (DSSCs). Compared to TB-1, the 5-hexyl and 3-hexyl substituted thiophene rings were introduced onto the TPA core in TTB-1 and TTB-2. Their photophysical, electrochemical and photovoltaic properties were investigated. The reference compound L1 (the triphenylamine counterpart of TB-1) was also evaluated for comparison. Compared to L1, the bridged triphenylamine based dyes studied showed enhanced performances, suggesting reasonable design of the new dyes. Meanwhile, the investigation of the three bridged TPA dyes demonstrated that by grafting 5-hexyl substituted thiophene onto the bridged TPA, TTB-1 had a significantly broader absorption spectrum in the UV–vis region, and thereby, its light harvesting ability was remarkably enhanced. Accordingly, the higher incident photon to current conversion efficiency (IPCE) of TTB-1 indicated a higher short-circuit current. In contrast, the 3-hexyl substituted thiophene in TTB-2 lead to larger steric hindrance, resulting in lower Jsc value. Similar structure of TTB-1 and TTB-2 afforded almost the same Voc. Therefore, dye TTB-1 showed the best performance, exhibiting power conversion efficiency of 4.35%, with Jsc of 8.61 mA cm−2 and Voc of 704 mV under simulated AM 1.5 irradiation (100 mW cm−2).

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