Synergistic Effect of Lewis Base Polymers and Graphene in Enhancing the Efficiency of Perovskite Solar Cells

Incorporating Lewis base polymers into a perovskite layer has been demonstrated as one of the most effective routes to passivate trap states at the grain boundaries, whereas the inferior electrical conductivity of polymers than that of perovskite would inevitably hinder charge transport across the perovskite grains. Herein, we reported a strategy of utilizing highly conductive graphene/Lewis base polymer (PM6 or PM7) composites as additives in perovskite, which simultaneously passivates the defects and facilitates charge transport in the film. We further revealed in the work that halogen elements (Cl/F) in the polymer (PM6/PM7) can p-dope the graphene and endow it with higher hole-transport selectivity, which is of critical importance as ambipolar charge transport without selectivity would induce significant charge recombination in graphene. By this design, we achieved an outstanding efficiency of 21.21%, which is significantly higher than that of the pristine device without treatment. The device also exhibited impressive stability by retaining 90% of its initial power conversion efficiency after 480 h aging in ambient air with a ∼35% relative humidity at room temperature.