Jeffrey DuBose – Hole Trapping in Halide Perovskites Induces Phase Segregation

Relevant papers:
https://pubs.acs.org/doi/abs/10.1021/...
https://pubs.acs.org/doi/abs/10.1021/...

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Talk Given by Jeffrey DuBose on the 26th of April 2023.
Abstract:
Metal halide perovskites have garnered a great deal of attention photovoltaic and optoelectronic applications. The ability to precisely tune the band gap of perovskites through compositional alloying of the halide ion is of particular interest for synthesizing tandem solar cells. However, under steady state light irradiation, an initially homogeneous mixed halide perovskite (MHP) will form local domains enriched in one halide ion (e.g., Br or I). This light-induced phase segregation forms iodide-rich domains that act as charge carrier traps and lowers the efficiency of perovskite-based devices, posing challenges for implementation of MHP devices. Interestingly, when a segregated MHP is placed in the dark, entropic driving forces prevail and the perovskite remixes to its initially homogeneous state. This talk will cover recent results that point to the specific role of hole trapping in driving phase segregation. Generation of holes either photochemically or electrochemically increases ion migration and leads to phase segregation. The thermodynamic properties of perovskites provide a strong driving force for hole trapping and oxidation of iodide species. However, mobile halide species within the perovskite lattice take time to migrate and generate halide-rich domains. When in contact with a nonpolar solvent, the migration of iodine species is further extended to expulsion of iodine from the perovskite film. Thus, the mobility of halides and their susceptibility to hole-induced oxidation play a crucial role in determining the long-term stability of metal halide perovskites. Strategies to gain kinetic control over ion migration to slow phase will be discussed. To achieve stability and improve the long-term efficiency of perovskite devices, suppression of segregation remains the key factor.