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<p>Dopant-free transition metal oxides are emerging as promising hole-selective contacts for crystalline silicon heterojunction solar cells. However, their performance is strongly governed by oxygen-vacancy-induced electronic disorder and unstable work function. In this study, sub-stoichiometric molybdenum oxide (MoO<sub>3-x</sub>) thin films were deposited by thermal evaporation and treated with ultraviolet-ozone (UVO) to tune their optical properties, stoichiometry, and work function. UV–Visible spectroscopy revealed enhanced optical transparency, with the average transmittance increasing from ~ 80% for the as-deposited film to ~ 85% after 30&#xa0;min of UVO treatment in the visible wavelength range, with optical bandgap values in the range of ~ 3.29–3.32&#xa0;eV for all MoO<sub>3-x</sub> films. Kelvin probe force microscopy showed a monotonic increase in work function from 4.61 to 5.03&#xa0;eV, with increasing UVO exposure, attributed to the reduction of donor-like oxygen vacancies. X-ray photoelectron spectroscopy revealed an increase in the Mo<sup>6+</sup>/Mo<sup>5+</sup> ratio and a systematic decrease in oxygen-vacancy concentration with increasing UVO treatment. Furthermore, the combined characterization results provide insight into the relationship between oxygen-vacancy concentration, Mo oxidation states, surface characteristics, and work-function variation of MoO<sub>3-x</sub> thin films. AFORS-HET simulations were further employed to provide qualitative insight into the influence of UVO-induced work-function variation on band alignment in MoO<sub>3-x</sub>/c-Si(n) heterojunctions.</p>

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Ultraviolet-ozone modulation of oxygen vacancies and work function in MoO3-x thin films for MoO3-x/c-Si(n) heterojunction solar cells

  • 期刊论文

  • 发表日期：

    2026年6月25日

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  • B. K. Keerthana,
  • Rahul,
  • Juhi Kumari,
  • Pratima Agarwal

摘要

Dopant-free transition metal oxides are emerging as promising hole-selective contacts for crystalline silicon heterojunction solar cells. However, their performance is strongly governed by oxygen-vacancy-induced electronic disorder and unstable work function. In this study, sub-stoichiometric molybdenum oxide (MoO3-x) thin films were deposited by thermal evaporation and treated with ultraviolet-ozone (UVO) to tune their optical properties, stoichiometry, and work function. UV–Visible spectroscopy revealed enhanced optical transparency, with the average transmittance increasing from ~ 80% for the as-deposited film to ~ 85% after 30 min of UVO treatment in the visible wavelength range, with optical bandgap values in the range of ~ 3.29–3.32 eV for all MoO3-x films. Kelvin probe force microscopy showed a monotonic increase in work function from 4.61 to 5.03 eV, with increasing UVO exposure, attributed to the reduction of donor-like oxygen vacancies. X-ray photoelectron spectroscopy revealed an increase in the Mo6+/Mo5+ ratio and a systematic decrease in oxygen-vacancy concentration with increasing UVO treatment. Furthermore, the combined characterization results provide insight into the relationship between oxygen-vacancy concentration, Mo oxidation states, surface characteristics, and work-function variation of MoO3-x thin films. AFORS-HET simulations were further employed to provide qualitative insight into the influence of UVO-induced work-function variation on band alignment in MoO3-x/c-Si(n) heterojunctions.