External Field-Tunable Internal Orbit-Orbit Interaction in Flexible Perovskites.

In hybrid metal halide perovskites, electrons carry both orbital and spin momenta through s-p wave function hybridization. This leads to a hypothesis that the orbit-orbit interaction between excitons can occur through orbital magnetic dipoles forming short-range interaction or through orbital polarizations forming long-range interaction to influence optoelectronic properties. This Letter reports an interesting phenomenon: the orbit-orbit interaction can be electrically switched between orbital magnetic dipoles and orbital polarizations in a flexible perovskite (MAPbI3-xClx) solar cell by scanning an external voltage between forward and reverse biases (0.2 and -0.2 V). Essentially, this phenomenon presents an external mechanism for electrically controlling the internal orbit-orbit interaction in hybrid perovskites. It was further observed that this bias-switchable orbit-orbit interaction is sensitive to temperature, becoming negligible when the temperature is decreased from 300 to 250 K. This observation indicates that the mobile ions driven by an external electrical field provide an intrinsic mechanism for electrically switching the orbit-orbit interaction through polarization and spin parameters while applying an external voltage between forward and reverse biases. These results provide a comprehensive understanding of tuning the orbit-orbit interaction in flexible perovskites toward developing orbitronic actions.