Degradation Dynamics of Perovskite Solar Cells Under Fixed Reverse-Current Injection

Previous studies of reverse-bias stability in perovskite solar cells have focused primarily on voltage-controlled tests. Here, we instead investigate perovskite solar cell degradation under well-defined, constant reverse-current stress. We show that the choice of hole-transport layer dictates the dominant degradation pathway: cells using thick poly(triphenylamine) (PTAA) layers can tolerate high reverse bias but quickly undergo catastrophic breakdown under fixed reverse current near their one-sun maximum power point. In contrast, cells modified with phosphonic-acid interface layer MeO-2PACz, with poorer indium-doped tin oxide (ITO) coverage compared to PTAA, exhibit gradual and recoverable degradation under certain stress and recovery conditions. For MeO-2PACz devices, degradation increases with both current magnitude and duration. Importantly, when normalized by injected charge (current times duration), lower currents applied over longer times cause more degradation than higher currents over shorter periods. Combining electrical measurements with spatially resolved photoluminescence imaging, our observations support an ion- and charge-mediated interfacial electrochemical degradation mode.