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<p>This study explores the influence of Li-based co-doping on the optoelectronic and photocatalytic performance of ZnO thin films synthesized via the dip-coating technique. Films of 5%Li–ZnO, 1%Mg–5%Li–ZnO, 1%La–5%Li–ZnO, and 1%Al–5%Li–ZnO were analyzed and compared with undoped ZnO. Structural analysis via XRD reveals that the 5%LiZnO film possesses the largest crystallite size (39&#xa0;nm), while the 1%Al–5%Li–ZnO shows the smallest (18&#xa0;nm). Optical studies show that 1%Mg5%Li–ZnO and 1%La–5%Li–ZnO have the widest bandgap energies of 3.46 eV, while pure ZnO has the narrowest at 3.41 eV. Electrochemical impedance analysis indicates that pure ZnO exhibits the highest polarization resistance (<i>R</i><sub>p</sub> = 237,280 Ω), corresponding to the lowest charge transfer efficiency. In contrast, Mg and Laco-doped films show significantly reduced R<sub>s</sub> and R<sub>p</sub> values, demonstrating enhanced electrical transport due to improved carrier mobility and reduced grain boundary barriers. This interpretation corrects the previous ambiguity regarding electrical performance. Photodetector evaluation indicates that pure ZnO exhibits the highest sensitivity (65.8), attributed to low dark current rather than superior conductivity. The reduced sensitivity of co-doped films is explained by their high dark current caused by increased carrier concentration, despite improved electrical transport properties. Photocatalytic tests demonstrate that 1%La–5%Li–ZnO achieves nearly 100% degradation of methylene blue under UV irradiation. Scavenger experiments confirm that holes (h⁺) and hydroxyl radicals (OH) are the dominant reactive species. The study emphasizes multifunctional optimization rather than a novel material composition.</p>

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Influence of 5% Li doping and 1% (Mg, La, Al) co-doping on the structural, optical, electrical transport, UV photodetection, and UV-driven photocatalytic degradation of methylene blue in dip-coated ZnO thin films: identification of h⁺ and ·OH reactive species

  • 期刊论文

  • 发表日期：

    2026年3月17日

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  • Sabrina Roguai,
  • Romaissa Allouche,
  • Abdelghani Lakel,
  • Abdelkader Djelloul

摘要

This study explores the influence of Li-based co-doping on the optoelectronic and photocatalytic performance of ZnO thin films synthesized via the dip-coating technique. Films of 5%Li–ZnO, 1%Mg–5%Li–ZnO, 1%La–5%Li–ZnO, and 1%Al–5%Li–ZnO were analyzed and compared with undoped ZnO. Structural analysis via XRD reveals that the 5%LiZnO film possesses the largest crystallite size (39 nm), while the 1%Al–5%Li–ZnO shows the smallest (18 nm). Optical studies show that 1%Mg5%Li–ZnO and 1%La–5%Li–ZnO have the widest bandgap energies of 3.46 eV, while pure ZnO has the narrowest at 3.41 eV. Electrochemical impedance analysis indicates that pure ZnO exhibits the highest polarization resistance (Rp = 237,280 Ω), corresponding to the lowest charge transfer efficiency. In contrast, Mg and Laco-doped films show significantly reduced Rs and Rp values, demonstrating enhanced electrical transport due to improved carrier mobility and reduced grain boundary barriers. This interpretation corrects the previous ambiguity regarding electrical performance. Photodetector evaluation indicates that pure ZnO exhibits the highest sensitivity (65.8), attributed to low dark current rather than superior conductivity. The reduced sensitivity of co-doped films is explained by their high dark current caused by increased carrier concentration, despite improved electrical transport properties. Photocatalytic tests demonstrate that 1%La–5%Li–ZnO achieves nearly 100% degradation of methylene blue under UV irradiation. Scavenger experiments confirm that holes (h⁺) and hydroxyl radicals (OH) are the dominant reactive species. The study emphasizes multifunctional optimization rather than a novel material composition.