Design, synthesis and photophysical properties of A-D-A-D-A small molecules for photovoltaic application

• Five small molecules for photovoltaic cells are described by an A-D-A-D-A structure.
• These molecules possess broad absorption spectrum and high absorption coefficient.
• High hole-mobility and energy level of these donor molecules match with that of PCBM.
• The DERH3TT-based cells exhibited maximum PCE of 3.19%.
• These molecules based devices showed broad photoelectric response from 300 to 800 nm.

A series of linear-conjugated small molecule compounds featured with the acceptor-donor-acceptor-donor-acceptor (A-D-A-D-A) structure were designed, synthesized and characterized. The films of the compounds showed a broad UV–Vis absorption range of 300–800 nm with high molar absorption coefficient of more than 1.0 × 104 cm−1. Their hole-mobility can be as high as 1.0 × 10−3 cm2 V−1 s−1. The compounds have a compatible HOMO energy level of −5.0 eV to PC71BM and a high solubility up to 20 mg mL−1 in chloroform. Therefore, compounds can blend with PC71BM in the chloroform and form an active layer for a photovoltaic cell device by spin-coating of the blend solution. A maximum power conversion efficiency of 3.2% was achieved with the DERH3TT solar cell device. These results indicate that the A-D-A-D-A small molecules with electron-withdrawing dyes as terminals are promising candidates for the high efficiency solution processed organic photovoltaic cells.

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