Doping Induced Orbit-Orbit Interaction between Excitons While Enhancing Photovoltaic Performance in Tin Perovskite Solar Cells

Doping has been used as a common method to improve photovoltaic performance in perovskite solar cells (PSCs). This paper reports a new phenomenon that the SnF₂ doping can largely increase the exciton-exciton interaction through orbital magnetic dipoles toward increasing dissociation probabilities in lead-free FASnI₂Br PSCs. Essentially, when orbit-orbit interaction between excitons occurs, linearly and circularly polarized photoexcitations can inevitably generate different photocurrents, giving rise to a ΔJ_sc phenomenon. Here, it is found that, when SnF₂ doping is used to boost photovoltaic efficiency to 7.61%, the orbit-orbit interaction is increased by a factor of 2.2, shown as the ΔJ_sc changed from 1.21% to 0.55%. Simultaneously, magnetic field effects of J_sc indicate that increasing orbit-orbit interaction leads to an increase on the spin-orbital coupling in Sn perovskites (FASnI₂Br) upon SnF₂ doping. This presents a new doping effect occurring in the Sn perovskite solar cell toward enhancing photovoltaic efficiency.