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<p>All-inorganic bismuth-based perovskites have emerged as promising candidates to replace lead-based perovskites due to their low toxicity and excellent environmental stability. However, the zero-dimensional (0D) structure of Cs<sub>3</sub>Bi<sub>2</sub>I<sub>9</sub> limits its charge transport capability, hindering its application in optoelectronic devices. In this work, a series of Br-doped Cs<sub>3</sub>Bi<sub>2</sub>I<sub>9-x</sub>Br<sub>x</sub> (x = 1–8) perovskite single crystals were successfully prepared via a modified anti-solvent vapor-assisted crystallization method, and their crystal structure, morphological evolution, and optoelectronic properties were systematically investigated. With increasing Br content, the crystals gradually transform from hexagonal prisms to hexagonal platelets, accompanied by a structural transformation from the 0D <i>P</i>6<sub>3</sub>/<i>mmc</i> phase to the 2D <i>P</i>–3<i>m</i> phase at the critical composition x = 3. At this transition point, Cs<sub>3</sub>Bi<sub>2</sub>I<sub>6</sub>Br<sub>3</sub> single crystals exhibit the highest crystallinity and the smallest band gap (1.86&#xa0;eV), as confirmed by UV–vis spectroscopy and further supported by density functional theory (DFT) calculations (calculated band gap ~ 1.8&#xa0;eV). Raman spectroscopy reveals the gradual disappearance of [Bi<sub>2</sub>I<sub>9</sub>]<sup>3−</sup> dimer vibrations and the emergence of Bi-Br vibrational modes, providing direct local structural evidence for the 0D → 2D transformation. A photodetector fabricated from the Cs<sub>3</sub>Bi<sub>2</sub>I<sub>6</sub>Br<sub>3</sub> single crystal exhibits a responsivity of 17.53&#xa0;mA W⁻<sup>1</sup>, a specific detectivity of 4.5 × 10<sup>10</sup> Jones, an on/off ratio of 125, and an external quantum efficiency (EQE) of 5.7% at 380&#xa0;nm. This study provides an effective strategy for regulating the dimensionality and band gap of bismuth-based perovskites, promoting their application in ultraviolet photodetection.</p>

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Structural transformation and dimensional control for high-performance photodetection in Cs3Bi2I9-xBrx perovskites

  • 期刊论文

  • 发表日期：

    2026年4月26日

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  • Zhiheng Liu,
  • Kaimin Wang,
  • Lang Gu,
  • Rui Shi,
  • Sancan Han

摘要

All-inorganic bismuth-based perovskites have emerged as promising candidates to replace lead-based perovskites due to their low toxicity and excellent environmental stability. However, the zero-dimensional (0D) structure of Cs3Bi2I9 limits its charge transport capability, hindering its application in optoelectronic devices. In this work, a series of Br-doped Cs3Bi2I9-xBrx (x = 1–8) perovskite single crystals were successfully prepared via a modified anti-solvent vapor-assisted crystallization method, and their crystal structure, morphological evolution, and optoelectronic properties were systematically investigated. With increasing Br content, the crystals gradually transform from hexagonal prisms to hexagonal platelets, accompanied by a structural transformation from the 0D P63/mmc phase to the 2D P–3m phase at the critical composition x = 3. At this transition point, Cs3Bi2I6Br3 single crystals exhibit the highest crystallinity and the smallest band gap (1.86 eV), as confirmed by UV–vis spectroscopy and further supported by density functional theory (DFT) calculations (calculated band gap ~ 1.8 eV). Raman spectroscopy reveals the gradual disappearance of [Bi2I9]3− dimer vibrations and the emergence of Bi-Br vibrational modes, providing direct local structural evidence for the 0D → 2D transformation. A photodetector fabricated from the Cs3Bi2I6Br3 single crystal exhibits a responsivity of 17.53 mA W⁻1, a specific detectivity of 4.5 × 1010 Jones, an on/off ratio of 125, and an external quantum efficiency (EQE) of 5.7% at 380 nm. This study provides an effective strategy for regulating the dimensionality and band gap of bismuth-based perovskites, promoting their application in ultraviolet photodetection.