Perovskite solar cells (PSCs) are a promising next-generation photovoltaic technology. Their device physics differs from that of conventional solar cells due to the ability of metal halide perovskites to conduct both electronic and ionic charge. The effects of mobile ions are often most pronounced in transient or frequency domain measurements due to ionic charge having a significantly lower mobility than electronic charge. As a result, the impact of mobile ions on steady state performance has attracted less attention, although it is of greater significance to device functionality given that solar cells are typically operated continuously at their maximum power point. In this thesis, we address this issue by using experimentally verified drift-diffusion simulations to investigate how mobile ions affect extraction and recombination processes in PSCs under steady state conditions. We show that mobile ions lead to diffusive electronic transport which results in electronic carrier accumulation under short-circuit conditions. However, by comparing our simulation results to measurements of PSCs’ bias-dependent photoluminescence quantum yield, we show that mobile ions alone cannot explain the experimental data. Instead, we find that the perovskite must also have a relatively low electronic carrier mobility. Furthermore, our simulations show that mobile ionic charge can increase the open-circuit voltage of PSCs, especially those in which non-radiative recombination losses are largely mediated by trap states located at perovskite/transport layer interfaces. We validate these findings using a novel experimental protocol which allows for a more accurate assessment of the impact of mobile ions on open-circuit voltage than is possible using existing methods. Based on these experimentally validated simulations, we propose that mobile ions increase the tolerance of PSCs to energetic offsets at the perovskite/transport layer interfaces, though at the cost of an increased sensitivity to the rate of recombination at these interfaces.