Electronic Properties of {111} Twin Boundaries in a Mixed-Ion Lead Halide Perovskite Solar Absorber

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We present first-principles theoretical predictions of the electronic properties of {111} twin boundaries in pure formamidinium lead iodide (FAPI) as well as a mixed-ion lead halide perovskite containing formamidinium, Cs, I, and Br. We find that the {111} twin boundary is extremely stable in pure FAPI but introduces no electron or hole trapping states and presents relatively small barriers (<100 meV) to transport of electrons and holes, suggesting that they are relatively benign for solar cell performance. However, in the mixed-ion perovskite, twin boundaries serve as a nucleation site for formation of an I- and Cs-rich secondary phase. The reduced band gap in this segregated phase leads to hole trapping and is likely to enhance electron–hole recombination and lead to reduced open-circuit voltage in solar cell devices. These results highlight the role of twin defects as nucleation sites for secondary phases, which can be extremely detrimental to solar cell performance.
Original languageEnglish
Pages (from-to)2663-2668
Number of pages6
JournalACS Energy Letters
Issue number11
Early online date4 Oct 2018
Publication statusPublished - 9 Nov 2018

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