The advances in halide perovskite-based optoelectronic devices originate from their unconventional semiconductor properties, including defect tolerance, strong light-matter interaction, a dynamic lattice, and a highly tunable electronic structure. Fully exploiting the potential of perovskites, therefore, demands a deeper understanding of their fundamental properties, encompassing charge-carrier dynamics, defect physics, and structure–property relationships. Building on the success of PeroFun25, we propose PeroFun26 at MatSus 2026 as a platform to highlight recent advances in the fundamental understanding of perovskite materials, with particular emphasis on their behavior in device-relevant architectures. In multilayer device stacks, interfaces can significantly alter charge, ionic, and optical processes; consequently, interface effects and strategies to mitigate interface-induced performance losses will be a central focus of the symposium. The symposium will emphasize emerging studies that probe composition, structure, optoelectronic properties, and ionic/electronic transport, especially those providing high spatial and temporal resolution. These approaches are critical for elucidating operational mechanisms and degradation pathways, enabling the rational design of more efficient and durable devices. Contributions on emerging perovskite-based applications, including field-effect transistors, thermoelectrics, memristive and neuromorphic devices, lasing, single-photon emission, polarized emission, and spintronics, are also welcomed