Over 20.1% Efficiency of Layer-by-Layer Organic Photovoltaics by Incorporating High Hole Mobility Material with...

Series of layer-by-layer organic photovoltaics (LOPVs) were constructed with polymer D18 as donor and small molecule L8-BO with self-dissociation characteristics as acceptor. The high hole mobility and good crystallinity semiconductor C8-BTBT was deliberately incorporated into the D18 and L8-BO layers for optimizing the performance of LOPVs. The power conversion efficiency (PCE) of LOPVs can be increased from 19.10% to 20.11% by incorporating 0.5 wt% C8-BTBT in D18 layer and 0.05 wt% C8-BTBT in L8-BO layer. The PCE improvement benefits from the synergistic enhancement of short circuit current density of 27.56 mA cm^-2 and fill factor of 80.10%. The incorporation of C8-BTBT in L8-BO layer can provide efficient transport channels for holes generated from L8-BO exciton self-dissociation. Introducing C8-BTBT in D18 layer can facilitate holes transport owing to its high hole mobility relative to that of D18. The interdiffusion between the D18 and L8-BO layers can be enhanced by incorporating highly crystalline C8-BTBT, facilitating exciton dissociation through enlarged donor/acceptor interfaces, as confirmed from neutron reflectivity measurements. This work indicates that incorporating high hole mobility material with good crystallinity into donor and acceptor layers is an effective strategy for achieving high-performance LOPVs.