Perylene diimide acceptor with two planar arms and a twisted core for high efficiency polymer solar cells

We design and synthesize two novel PDI based acceptors VDP-Se and NDP-Se. VDP-Se with a central vinylene core presents a slightly twisted molecular conformation; whereas, the fused NDP-Se possesses a distorted naphthalene core, an X-shaped skeleton and two planar PDI units. The twisted conformations of these two acceptors can effectively prevent them from forming large aggregates when blended with the polymer donor. Photovoltaic characterizations demonstrate PCEs of 6.01% and 6.85% for VDP-Se and NDP-Se based devices, respectively. Higher and more balanced charge carrier mobility of NDP-Se based devices can account for its better photovoltaic performance. The morphology of PBDB-T:NDP-Se blend films can be slightly optimized by the addition of DIO and an improved PCE of 7.41% (V-oc = 0.94 V, J(sc) = 12.68 mA/cm(2) and FF = 61.89%) is finally achieved. Our studies demonstrate that the twisted core can effectively suppress the exhausted intermolecular aggregation and the planar PDI units can form better charge transporting channels. Such combined planar and twisted strategy can be an effective way to design PDI based acceptors for high efficiency PSCs.