Synthesis of star-shaped small molecules carrying peripheral 1,8-naphthalimide functional groups and their applications in organic solar cells

• Star-shaped D-A molecules were synthesized by direct C–H activation and Suzuki cross-coupling.
• Star-shaped molecules were used as donor materials for organic solar cells.
• 1,8-Naphthalimide, triphenylamine, and oligothiophene were used the acceptor, the donor and the spacer, respectively.

A series of novel star-shaped small molecules with triphenylamine as the core, oligothiophene as the spacer and 1,8-naphthalimide as the electron withdrawing end-group were synthesized and used as donor materials for solution-processed organic solar cells. Direct arylation and Suzuki cross-coupling were used to synthesize the key intermediates and star-shaped molecules. The star-shaped molecules showed good thermal stability, intense absorption in the range of 300–700 nm, and deep HOMO energy level. A bulk heterojunction organic solar cell with one of the star shaped molecules in combination with PC71BM as the active layer gave a power conversion efficiency of 2.32% with a high open-circuit voltage up to 0.94 V. The influence of the spacer between the triphenylamine core and the peripheral 1,8-naphthalimide function group on the optical and photovoltaic properties was also investigated. Our studies indicated that 1,8-naphthalimide can be used as a promising building block for the synthesis of novel donor materials for organic solar cells.

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