Single-layered organic photovoltaics with double cascading charge transport pathways: 18 % efficiencies

Abstract The chemical structure of donors (Ds) and acceptors (As) limit the power conversion efficiencies (PCEs) achievable with bulk heterojunction (BHJ) active layers of binary D-A mixtures. However, using quaternary D-A blends, double cascading energy level alignment in BHJ organic photovoltaic active layers are realized, enabling efficient carrier splitting and transport. Numerous avenues to optimize light absorption, carrier transport, and charge transfer state energy levels are opened by the chemical constitution of the components. Record-breaking PCEs of 18.07% are achieved where, by electronic structure and morphology optimization, simultaneous improvements of the open-circuit voltage, short-circuit current and fill factor occur. The D and A chemical structures afford control over electronic structure and charge transfer state energy levels, enabling manipulation of hole-transfer rates, carrier transport, and non-radiative recombination losses.