Negative photoconductivity as a quantitative probe of sulfur vacancies in MoS2 photoelectrodes

Nguyen Xuan Chung, Pham Duc Thang, L.V.C. Hau, Nguyen Ba Huy Hoang, Nguyen Duy Thien, Tien Dai Nguyen, Thuan Dao Nguyen, T.T.K. Chi, Thi Bich Vu, Tien-Thanh Nguyen

Applied Surface Science, Volume 752, January 2027, 168207

DOI: 10.1016/j.apsusc.2026.168207

Abstract

This report demonstrates a quantitative and non-destructive approach to evaluate sulfur vacancies in hydrothermally synthesized MoS₂ by using negative photoconductivity as a probe of defect-mediated carrier dynamics. While X-ray diffraction and Raman parameters, such as the (0 0 2) peak position (14.06–14.12°) and Raman mode separation (Δω ≈ 28.7–30.3 cm⁻¹), show negligible or non-systematic variation, the normalized photoresponse efficiency (η) exhibits a clear monotonic dependence on precursor ratio. A multilevel framework is developed in which η–potential curves are analyzed using a sigmoidal model to extract the saturation efficiency, followed by Langmuir and Boltzmann formalisms to quantify defect density. With calibration against four independent XPS measurements, the sulfur vacancy concentration is estimated to range from approximately 4.6% to 11.8% across the sample series (MS11–MS18). These results establish negative photoconductivity as a sensitive probe that reproduces the same sample-to-sample ranking of defect density as XPS, providing a low-cost alternative for defect engineering in MoS₂ and related two-dimensional materials.