Perovskite solar cells (PSCs) can reach power conversion efficiencies above 26% through simple fabrication methods, offering key advantages over established photovoltaic technologies. Yet, for PSCs to contribute to the energy transition, their operational stability must be improved. The mixed ionic-electronic conductivity of the metal halide perovskite absorber induces reversible and irreversible performance changes linked to electric field-driven ionic accumulation. The extent to which PSCs are affected by mobile ions depends on the interplay between ionic and electronic properties, with stability determined by how these evolve over time.

This thesis investigates how ion migration affects PSC device physics, using simulations and experiments based on innovative characterization approaches. Electroluminescence (EL) is key for perovskite LEDs (PeLEDs), but also provides vital information on the origin of recombination losses in PSCs. The effect of ionic redistribution on transient EL of PeLEDs and PSCs is studied. Mobile ions show a double-edged role, enhancing radiative recombination in some cases while impairing it in others, depending also on interactions with charge transport layers. Performance changes often attributed to 'light soaking' under illumination are also observed in the dark under forward bias, highlighting the dominant role of ion migration.

Under current extraction, ionic accumulation can screen the electric field, reducing the driving force for charge collection. Because the perovskite absorption coefficient depends on wavelength, spectral changes in external quantum efficiency (EQE) under different preconditioning voltages reveal how collection efficiency depends on ionic distribution. When recombination competes with extraction, the slow response of mobile ions can lead to scan rate-dependent J-V hysteresis, sometimes causing an anomalous photocurrent maximum ('bump') before short-circuit. By controlling temperature, preconditioning, and bias sequence of EQE measurements to reflect conditions of rate-dependent scans, J-V curves can be reconstructed with spectral information, helping to visualize the effects of ion dynamics. Temperature variation mimics different scan rates by affecting ionic mobility. This method, combined with simulations, explains current losses for both normal and inverted hysteresis, where negative effects from polarity inversion of ionic accumulation layers dominate. Key considerations for optimizing carbon-based triple mesoscopic PSCs are provided with a focus on ionic effects.

Combining EQE with optical simulations enables, for the first time, extraction of the spatial collection efficiency (SCE) of PSCs. The method is validated with simulations and demonstrates SCE analysis as a powerful tool to study ionic effects. Simulations clarify how mobile ions influence PSC performance and stability depending on device-specific properties, and how ion-induced performance losses or gains can be measured during degradation. Finally, the sign of the low-frequency capacitance of PSCs is shown to depend on the ionic modulation of recombination. The insights presented, supported by measurements and simulations, elucidate how the interplay between ionic and electronic properties governs PSC performance and stability, and provide effective methods to analyze performance changes arising from ion migration.