As-cast organic solar cells with 19.44% efficiency enabled by introducing functional fullerene derivative to facilitate charge carrier generation and transport

The reduced donor/acceptor interfacial area and relatively low electron mobility of fused ring electron acceptors confine charge carrier generation and transport in current sequential layer-by-layer (LbL) processed organic solar cells (OSCs), thus limiting the further improvement of power conversion efficiencies (PCEs). In view of the good compatibility and high electron mobility of fullerene, herein we develop a new fullerene derivative, FU-MO, and introduce it into the acceptor layer of LbL OSCs based on the D18/Y6 pair. FU-MO possesses good miscibility with the polymer donor, D18, and excellent electron mobility, which endows the D18/Y6+FU-MO blend film with shorter d-spacing, larger crystalline coherence length, improved crystal quality and optimized phase separation. Such enables D18/Y6+FU-MO based LbL devices to achieve reduced trap density, higher charge carrier mobilities, shrinkable extraction time and prolonged charge carrier lifetime, thus facilitating exciton dissociation and suppressing charge carrier recombination, compared with the pristine D18/Y6 counterparts. Therefore, D18/Y6+FU-MO based as-cast LbL OSCs gain a superior PCE of 19.44%, which is among the highest values for as-cast OSCs so far. This work demonstrates that introducing functional fullerene derivatives is an efficient route to boost PCEs of LbL OSCs.