Metal halide perovskites, owing to straightforward bandgap tuning through halide stoichiometry variation, have shown great potentials in various optoelectronic devices. However, unwanted halide segregation under operational conditions restricts practical applications, and the mechanism behind remains unclear.

In this presentation, I will first introduce a photoelectrochemical model to rationalize both light-induced and voltage-induced halide segregation. Second, I will focus on voltage-induced halide segregation and discuss the impact of voltage bias on halide perovskite devices. We identified various voltage thresholds and visualized voltage-induced halide redistribution in mixed-halide perovskite devices. Moreover, we demonstrated that monolithic perovskite/silicon tandem solar cells, compared to perovskite single-junction devices, show superior reverse-bias resilience. Third, I will switch gears to light-induced halide segregation and discuss the effect of organic hole transport layers (HTLs) on perovskite photoluminescence behavior. We showed that the HTL’s highest occupied molecular orbital energy dictates light-induced halide segregation and halogen diffusion at perovskite/organic HTL interfaces. Furthermore, we experimentally revealed the correlation between halide segregation and iodide oxidation via in-situ opto-gravimetric measurements. Finally, I will talk about the challenges and future research directions for the commercialization of perovskite photovoltaics, and present our attempt to mitigate iodine diffusion by using a MoO₃-organic composite HTL.

Adviser: Barry Rand