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<p>In this work, we report a comprehensive study of the structural, optical, and photoelectrical properties of one-dimensional (1D) CsCu<sub>2</sub>Br<sub>3</sub> single crystals. Powder X-ray diffraction (XRD) confirms the orthorhombic Cmcm phase with excellent crystallinity, while thermogravimetric analysis (TGA) demonstrates thermal stability up to ~ 300&#xa0;°C, with only a minor (~ 6%) extrinsic mass loss near 287&#xa0;°C. Optical characterization reveals a direct bandgap of 4.09&#xa0;eV, a low Urbach energy (0.104&#xa0;eV), and strong blue photoluminescence (451.6&#xa0;nm) with a large Stokes shift and unusually broad full width at half maximum (FWHM) (~ 250&#xa0;nm), indicative of pronounced electron–phonon coupling and self-trapped excitons (STEs). Time-resolved PL yields two recombination channels (<i>τ</i><sub>1</sub> = 10.07&#xa0;ns, <i>τ</i><sub>2</sub> = 2.27&#xa0;ns), consistent with free/shallow carriers and stabilized STEs. Electrical measurements show symmetric Current–voltage (I–V) behavior and UV-enhanced conduction dominated at high fields by a trap-limited space-charge-limited current (SCLC) mechanism (<i>m</i>&#xa0;≈&#xa0;2.45, <i>V</i><sub><i>TFL</i></sub>&#xa0;≈&#xa0;13.2&#xa0;V). Under 365&#xa0;nm excitation (photon energy below E<sub>g</sub>), the device exhibits a reproducible but modest photoconductive response, mediated by sub-gap absorption pathways—namely Urbach-tail states, defect-related channels, and STE manifolds—rather than direct interband excitation. Accordingly, the responsivity at 365&#xa0;nm is modest (R&#xa0;≈&#xa0;4.38 × 10<sup>−5</sup>&#xa0;A W<sup>−1</sup>), requires a higher bias (+ 20&#xa0;V), and shows trap-limited SCLC signatures, fully consistent with a weak sub-gap absorption regime. Collectively, the structural robustness, stable excitonic blue emission, and sub-gap mediated UV photoresponse position CsCu<sub>2</sub>Br<sub>3</sub> as a durable lead-free platform for UV optoelectronics, with maximum efficiency expected under deep-UV excitation (≈&#xa0;280–320&#xa0;nm), to be mapped in future calibrated spectral responsivity studies.</p>

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Stable blue emission and sub-gap mediated UV photodetection in lead-free 1D CsCu2Br3 single crystals

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  • 发表日期：

    2025年10月14日

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  • Mohamed Bouzidi,
  • Abdullah A. Alatawi,
  • Turki Alkathiri,
  • Sultan Albarakati,
  • Norah Alwadai,
  • Hammadi Khmissi,
  • Mohamed Ben bechir

摘要

In this work, we report a comprehensive study of the structural, optical, and photoelectrical properties of one-dimensional (1D) CsCu2Br3 single crystals. Powder X-ray diffraction (XRD) confirms the orthorhombic Cmcm phase with excellent crystallinity, while thermogravimetric analysis (TGA) demonstrates thermal stability up to ~ 300 °C, with only a minor (~ 6%) extrinsic mass loss near 287 °C. Optical characterization reveals a direct bandgap of 4.09 eV, a low Urbach energy (0.104 eV), and strong blue photoluminescence (451.6 nm) with a large Stokes shift and unusually broad full width at half maximum (FWHM) (~ 250 nm), indicative of pronounced electron–phonon coupling and self-trapped excitons (STEs). Time-resolved PL yields two recombination channels (τ1 = 10.07 ns, τ2 = 2.27 ns), consistent with free/shallow carriers and stabilized STEs. Electrical measurements show symmetric Current–voltage (I–V) behavior and UV-enhanced conduction dominated at high fields by a trap-limited space-charge-limited current (SCLC) mechanism (m ≈ 2.45, VTFL ≈ 13.2 V). Under 365 nm excitation (photon energy below Eg), the device exhibits a reproducible but modest photoconductive response, mediated by sub-gap absorption pathways—namely Urbach-tail states, defect-related channels, and STE manifolds—rather than direct interband excitation. Accordingly, the responsivity at 365 nm is modest (R ≈ 4.38 × 10−5 A W−1), requires a higher bias (+ 20 V), and shows trap-limited SCLC signatures, fully consistent with a weak sub-gap absorption regime. Collectively, the structural robustness, stable excitonic blue emission, and sub-gap mediated UV photoresponse position CsCu2Br3 as a durable lead-free platform for UV optoelectronics, with maximum efficiency expected under deep-UV excitation (≈ 280–320 nm), to be mapped in future calibrated spectral responsivity studies.