Approaching 18% efficiency of ternary layer-by-layer polymer solar cells with alloyed acceptors

In this work, ternary layer-by-layer (LbL) polymer solar cells (PSCs) were prepared with D18-Cl/Y6 as host system and MAZ-2 as the second acceptor. The open circuit voltage (VOC) of LbL PSCs can be increased with the addition of MAZ-2, signifying the alloy state formation between Y6 and MAZ-2 with good compatibility. A power conversion efficiency (PCE) of 17.98% can be achieved in the optimal ternary LbL PSCs with acceptor layer prepared from Y6:MAZ-2 (10:1, wt/wt) blend solution, accompanying with synchronously improved short circuit current density (JSC) of 27.10 mA cm−2, open circuit voltage (VOC) of 0.88 V and FF of 75.39% as compared to those of host binary system. The JSC improvement of ternary LbL PSCs should be closely related to more efficient exciton utilization through the additional channel of intermolecular energy transfer from MAZ-2 to Y6. The interfacial energy between donor and acceptor layer can be increased by adding MAZ-2 with lower compatibility with D18-Cl, which may lead to the weakened interpenetration of acceptor into donor layer to form more ideal vertical phase separation for efficient charge transport and collection. This work provides a guidance to select the third component having appropriate compatibility with host materials for realizing performance improvement of LbL PSCs.