Solution-processable, π-extended small molecule (SM) donors and acceptors are promising alternatives to polymer donors and fullerenes, respectively, in bulk-heterojunction (BHJ) solar cells. With single-cell device efficiencies &gt;10% now in reach, further efficiency improvements with π-extended SM systems require forging a better understanding of how molecular structure and functional substitutions direct the occurrence of molecular packing effects, specific BHJ morphologies and, in turn, carrier transport and recombination effects in thin-film devices. Our recent studies with various sets of analogous SM donor systems indicate that main-chain substitutions and donor-acceptor unit sequences largely impact all of the aforementioned material and thin-film characteristics, yielding a broad range of efficiencies in BHJ solar cells: from ca. 1% to &gt;8%. Our parallel effort on SM acceptors that can serve as fullerene alternatives in efficient BHJ solar cells with polymer donors indicates that adequate functional end-group substitutions can effectively promote the electron-transport character of the p-extended backbone, and we show that efficiencies of up to ca. 10% can be achieved when polymer donors with complementary spectral absorption are employed. Achieving favorable morphologies and comparable device efficiencies with “all-SM blends” composed of SM donor and SM acceptor counterparts proves more challenging.

Solution-processable molecular donors & acceptors for efficient bulk-heterojunction solar cells

253rd National Meeting (2017)

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