Metal halide perovskites, owing to their straightforward bandgap tuning through variations in halide stoichiometry, have demonstrated significant potential in various optoelectronic devices. However, unwanted halide segregation under operational conditions, such as light illumination and voltage bias, limits practical applications, and the underlying mechanisms still require in-depth investigation. In this thesis, we experimentally explore both voltage-induced and light-induced halide segregation to uncover the photoelectrochemical origins of this phenomenon. We start with an examination of voltage-induced halide segregation and study the impact of voltage bias on halide perovskite devices. Through conducting a series of prolonged volt- age biasing tests, complemented by extensive characterization techniques, we identify various voltage thresholds in mixed-halide perovskite devices and directly visualize the voltage-induced halide redistribution. Furthermore, we show that monolithic perovskite/silicon tandem solar cells exhibit superior reverse-bias resilience compared to perovskite single-junction devices, positioning them at a higher technology readiness level for addressing the challenge of partial shading. Lastly, we delve into light- induced halide segregation and examine the effect of organic hole transport layers (HTLs) on the photoluminescence behavior at perovskite/organic HTL interfaces. We demonstrate that the highest occupied molecular orbital energy of the HTL in- fluences the reactivity of the I2/HTL redox reaction, halogen diffusion, and light- induced halide segregation at these interfaces. Our findings offer new insights into a variety of voltage-induced and light-induced instabilities in halide perovskite materials and devices from a photoelectrochemical standpoint, guiding the development of perovskite-based optoelectronic devices towards stable operation.

Adviser: Barry Rand