Engineering optoelectronic properties of two-dimensional transition metal dichalcogenides via acid treatment: defect manipulation mechanisms and the optical–electrical trade-off

Two-dimensional transition metal dichalcogenides (TMDs) are promising candidates for next-generation optoelectronics, but their performance is often constrained by intrinsic defects. Acid treatment has emerged as a powerful defect engineering strategy, dramatically boosting the photoluminescence (PL) quantum yield of these atomically thin semiconductors. This review systematically examines progress in acid-induced PL enhancement of TMDs over the past decade and distills the underlying mechanisms and ongoing controversies. A central theme is the ubiquitous trade-off: optical properties improve markedly, whereas electrical transport in field-effect transistors frequently degrades after treatment. This counterintuitive behavior is rationalized through a sulfur vacancy-mediated hopping transport model, which shows that the trade-off is an inherent consequence of defect manipulation rather than a side effect. Moving beyond this compromise, synergistic design rules for decoupling optical and electronic responses are critically assessed, with particular emphasis on the emerging use of Lewis acids for targeted property modulation. Finally, future research directions are outlined, including integrating machine learning with atomic-scale defect characterization, testing the generality of defect‑selective passivation across diverse defects, and advancing these strategies toward practical device applications.