DEFESA DE TESE DE DOUTORADO #445 – EVERTON PEREIRA DE ANDRADE – 06/10/2025

This doctoral thesis investigates the optoelectronic properties of metal halide perovskite (MHP) nanowires, with emphasis on heterostructured CsPb(Br₁₋ₓClₓ)₃ systems. The nanowires were synthesized using a template-assisted epitaxial growth process followed by controlled gas-phase anion exchange in an Ar/Cl2 atmosphere, enabling the formation of axially stepped heterojunctions with tunable halide composition. Atomic force microscopy (AFM) revealed high morphological uniformity, with average lengths of 3-5 μm and diameters of 250 nm. Photoluminescence (PL) mapping demonstrated clear spectral gradients across the heterojunction, with emission peaks shifting from 523 nm in the Br-rich region to 507 nm in the Cl-rich region.
Temperature-dependent PL and time-correlated single-photon counting (TCSPC) measurements revealed a remarkable enhancement of exciton lifetimes near crystallographic phase transitions, particularly around 305 K in the Cl-rich domains and 361 K in Br-rich nanowires. Bi-exponential decay analysis showed that while the radiative recombination channel remained nearly stable, the non-radiative channel exhibited a pronounced slowdown at the transition, leading to lifetimes up to three times longer than the baseline values. This behavior was reproducible across multiple thermal cycles and was accompanied by hysteresis in the PL peak position, indicating structural reordering.
To interpret these results, the nanowires are modeled as disordered strain superlattices, where ferroelastic domains and flexoelectric polarization gradients modulate the electronic band structure and exciton dynamics. This framework highlights the interplay between strain, phase transitions, and carrier recombination in low-dimensional perovskite systems.
Overall, this work provides fundamental insights into how structural phase transitions extend exciton lifetimes and tune the optical response of CsPb(Br₁₋ₓClₓ)₃ nanowires. These findings establish design principles for exploiting ferroelasticity and flexoelectricity in perovskite nanostructures, with direct implications for high-efficiency optoelectronic devices such as solar cells, light-emitting diodes, and photodetectors operating under elevated temperatures and concentrated illumination.

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