Organic photovoltaics (OPVs) are promising candidates for providing a low cost, widespread energy source by converting sunlight into electricity. Solution-processable active layers have predominantly consisted of a conjugated polymer donor blended with a fullerene derivative as the acceptor. Although fullerene derivatives have been the dominant electron acceptors in organic photovoltaics, they have limitations, including poor absorption in the visible to near-IR and limited tuning of the energy levels. There is strong interest in discovering new electron acceptors that may overcome these limitations. Here, we present our work in developing non-fullerene acceptors based on azadipyrromethenes (ADP). Azadipyrromethenes are ligands with strong absorption in the visible to near-IR, high electron affinity, and tunable energy levels through substitutions and chelation. New azadipyrromethenes with arylethynyl substituents were synthesized, characterized and coordinated with BF2+ and transition metals. The azadipyrromethenes were tested in organic solar cells using regioregular poly(3-hexylthiophene) as the donor material. Free ligands and BF2+ chelates showed poor device performance due to aggregation in blends. On the other hand, homoleptic complexes of Zn(II) showed good performance, and the presence of arylethynyl substituents in the pyrollic positions was key to obtaining a favorable morphology in blends and a power conversion efficiency as high as 4%. The high efficiency is attributed to the acceptor’s 3D structure that prevents crystallization and promotes a favorable morphology in blends.

Alternative electron acceptors based on azadipyrromethene complexes for bulk heterojunction organic solar cells

252nd National Meeting (2016)

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