Proceedings of nanoGe Fall Meeting 2021 (NFM21)
DOI: https://doi.org/10.29363/nanoge.nfm.2021.197
Publication date: 23rd September 2021
Photo-induced halide segregation is critical to the stability of multijunction photovoltaic-compatible mixed-halide (iodide-bromide) 3D perovskites. However, the effect is not well understood in mixed-halide lower-dimensional (2D or quasi-2D) perovskites whose superior environmental stability can improve long-term performance. In this work, we study phenethylammonium-based mixed-halide 2D (PEA2Pb(I1-xBrx)4) and quasi-2D (PEA2MAn-1Pbn(I1-xBrx)3n+1) perovskite thin films and characterize the slow occurrence of halide segregation under illumination and its reversal in the dark. Time-dependent photoluminescence spectroscopy shows that a system’s propensity to undergo halide demixing strongly depends on its structural nature. While a pure-2D (n=1) system is largely immune to the light-induced demixing of halides, other structural phases (n>1) comprised of conjoined lead halide octahedral sheets show a lower tolerance to such stressors and consequently form low-energy iodide-rich traps. In multi-dimensional (nominally n=4) thin film systems, the distribution of these phases (n=1, 2…∞), and consequently the stability, are shown to be regulated through solvent-engineering strategies. Differences in ion migration behaviour between structural phases also influences entropy-driven ionic remixing in the dark, which successfully restores the statistical mixed-halide composition in higher-dimensional phases but not in lower-dimensional analogs. These observations therefore establish perovskite dimensionality as a key determinant to the photo-stability of lower-dimensional perovskite optoelectronic devices.
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