Crowning of dibenzosilole with a naphthalenediimide functional group to prepare an electron acceptor for organic solar cells

• Conjoint use of dibenzosilole (DBS) and naphthalenediimide (NDI) functionalities to develop a novel non-fullerene acceptor.
• Incorporation of peripheral donor atoms containing lypophilic chains in order to enhance solubility.
• Highly conjugated and well-proportioned target material which possesses energy levels matching with those of P3HT.
• BHJ device afforded FF which is amongst the top values for a small molecular non-fullerene acceptor.

A novel, solution-processable non-fullerene electron acceptor 9,9′-(5,5-dioctyl-5H-dibenzo [b,d]silole-3,7-diyl)bis(2,7-dioctyl-4-(octylamino)benzo[lmn][3,8]phenanthroline-1,3,6,8(2H,7H)-tetraone) (B3) based on dibenzosilole and naphthalenediimide building blocks was designed, synthesized, characterized and successfully used in a bulk-heterojunction organic solar cell. B3 displayed excellent solubility, thermal stability and acquired electron energy levels matching with those of archetypal donor polymer poly(3-hexylthiophene). Solution-processable bulk-heterojunction devices afforded 1.16% power conversion efficiency with a high fill factor of 53%. B3 is the first example in the literature using this design principle, where mild donor units at the peripheries of end-capped naphthalenediimide units tune solubility and optical energy levels simultaneously.

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