Understanding The Impact of Ions on Open Circuit Voltage in Perovskite Solar Cells

Metal halide perovskites are a nascent class of materials that combine competitive power conversion efficiencies with low-cost materials and manufacturing processes for use in next-gen solar cells. These materials, uniquely amongst PV materials, are capable of conducting both ionic and electronic charge. However, the presence of mobile ions can lead to extraction losses and carrier accumulation, as a function of the applied bias history of the device which can lead to unreliable performance. However, mobile ions can also reduce recombination currents at the perovskite/transport layer interfaces, increasing open-circuit voltage (V_oc). Employing Stabilise-and-Pulse (SaP) measurements, we show that ion accumulation can increase V_oc by 0.1 V, which decreases as the flat-ion potential of the PSC becomes larger. We validate these results with drift-diffusion simulations and confirm that under poor energetic alignment conditions, ions can provide a significant boost to the device performance.