Addressing dynamic photovoltaic processes at electrode:active layer and donor:acceptor interfaces in organic solar cells under device-operating conditions

This article presents our experimental studies to unravel the dynamic photovoltaic processes occurring at donor:acceptor (D:A) and electrode:active layer (E:A) interfaces under device-operating conditions by using two unique magneto-optical measurements, namely photo-induced capacitance and magnetic field effect measurement. First, we have found that a higher surface polarization of dielectric thin film can decrease the surface charge accumulation at E:A interface. The photo-induced capacitance results indicate that dielectric thin film plays a crucial role in the charge collection in generating photocurrent in organic solar cells. Second, our experimental results from magnetic field effect show that the binding energies of charge transfer (CT) states at D:A interface can be evaluated by using the critical bias required to completely dissociate the CT states. This is the first experimental demonstration that the binding energies of CT states can be measured under deviceoperating conditions. Furthermore, we use our measurement of magnetic field effect to investigate the most popular organic photovoltaic solar cells, organometal halide perovskite photovoltaic devices. The results of magneto-photoluminescence show that the photogenerated electrons and holes are inevitably recombined into electron-hole pairs through a spin-dependent process in the perovskites. Therefore, using spin polarizations can present a new design to control the photovoltaic loss in perovskites-based photovoltaic devices. Also, we found that introducing D:A interface can largely affect the bulk charge dissociation and recombination in perovskite solar cells. This indicates that the interfacial and bulk photovoltaic processes are internally coupled in developing photovoltaic actions in perovskite devices. Clearly, these magneto-optical measurements show a great potential to unravel the deeper photovoltaic processes occurring at D:A and E:A interfaces in both organic bulk-heterojunction and perovskite solar cells under device-operating conditions.