What if the tiny atomic flaws inside a semiconductor could become a design tool instead of a performance killer? For two-dimensional transition metal dichalcogenides (TMDs), the atomically thin materials widely regarded as a frontier platform for next-generation optoelectronics, this question has never been more relevant. Sulfur vacancies, atomic-scale holes inevitably created during growth, can depress photoluminescence quantum yields (PL QYs) to as low as 0.01%, cut carrier mobility by orders of magnitude, and slow photodetector response times. Now, researchers from Northeast Normal University and Neijiang Normal University in China have delivered a systematic account of how acid treatment, one of the most powerful “defect engineering” strategies, can turn these flaws into a tunable knob for optoelectronic performance. The review has been published in the journal Nano Research on August 5, 2026.
The story begins with a striking observation. Since 2015, superacid treatments such as bis(trifluoromethane)sulfonimide (TFSI) have been shown to boost the PL QY of monolayer molybdenum disulfide (MoS 2 ) and tungsten disulfide (WS 2 ) toward near-unity values, with enhancements of up to 190-fold and lifetimes lengthened from 0.3 to 10.8 nanoseconds. “Acids act like a molecular medicine for these atomically thin materials,” explains Assoc. Prof. Yuanzheng Li, corresponding author. “They repair sulfur vacancies and reshape the carrier population, allowing monolayers to emit light almost perfectly.”
But there is a paradox: the same treatment that makes TMDs shine often makes their transistors sluggish. TFSI-treated field-effect transistors frequently show degraded carrier mobility, and in some cases a two-order-of-magnitude drop. “For years, researchers treated optical enhancement and electrical degradation as separate stories,” says Prof. Weizhen Liu, corresponding author. “Our review shows they are two sides of the same coin.” The key, the team argues, is a sulfur-vacancy-mediated hopping transport model: in the low-carrier-density regime, sulfur vacancies themselves act as hopping sites that carry current, so passivating them removes the very conduction pathway. This counterintuitive mechanism explains why optical improvement can come at the cost of electrical transport.
The review also disentangles the competing mechanisms behind acid-induced PL enhancement: H + -mediated passivation, cation-induced p-type doping, and synergistic H + /anion effects, each supported by distinct experimental evidence. Intriguingly, a completely non-acidic analogue (TFEA) still produces strong PL enhancement, challenging all three models and suggesting that the underlying chemistry may be system-dependent. “The mechanism debate is far from settled,” notes Li. “Resolving it will require watching acid molecules interact with defects at the atomic scale, which is where machine learning comes in.”
Moving beyond the trade-off, the authors critically assess strategies for decoupling optical and electronic responses. A two-step thiol–acid passivation, for example, preserves near-pristine mobility while maintaining the benefits of p-type doping, and protective capping layers or corrosion-resistant electrodes tame acid-induced damage. The review further highlights Lewis acids such as SnCl 4 , PtCl 4 , and FeCl 3 as a complementary paradigm: unlike Brønsted acids, they dope TMDs substitutionally, enabling record-low contact resistance, lateral p–n homojunctions for photodetectors, and photoelectric synaptic devices with ultralow energy consumption of about 0.1 femtojoule per event.
Across the device landscape, acid-induced doping has already powered homojunction photodetectors, logic inverters, ternary logic gates, light-emitting devices, and neuromorphic synapses. The review reframes these advances within a single knowledge framework that connects atomic-scale mechanisms to macroscopic device functionality, from passive defect passivation to active functionality design.
Looking ahead, the team outlines three priorities: integrating machine learning with atomic-scale defect characterization to resolve the mechanistic debate; extending defect-selective passivation beyond sulfur vacancies to metal vacancies, antisites, and grain boundaries; and overcoming practical barriers such as ambient instability, thermal limits, and poor reproducibility. “If acid treatment can be made stable and scalable, it could become a standard tool in future fabs,” says Liu. “Our ultimate goal is to give researchers a general blueprint for energy-efficient, high-performance 2D optoelectronics.”
The review was authored by Qiushi Feng (Neijiang Normal University) together with Yuanzheng Li and Weizhen Liu (Northeast Normal University). The work was supported by the National Key Research and Development Program of China (No. 2023YFB3610200), the National Natural Science Foundation of China (Nos. 12474421, 62574038 and 62275045), and the Science and Technology Development Plan Project of Jilin Province, China (Nos. 20260101043JJ and 20240601049RC).
DOI Link:
https://doi.org/10.26599/NR.2026.94909086
About Nano Research
Nano Research is a peer-reviewed, open access, international and interdisciplinary research journal, sponsored by Tsinghua University and the Chinese Chemical Society, published by Tsinghua University Press on the platform SciOpen. It publishes original high-quality research and significant review articles on all aspects of nanoscience and nanotechnology, ranging from basic aspects of the science of nanoscale materials to practical applications of such materials. After 18 years of development, it has become one of the most influential academic journals in the nano field. Nano Research has published more than 1,000 papers every year from 2022, with its cumulative count surpassing 8,000 articles. In 2025 InCites Journal Citation Reports, its 2025 IF is 9.4 (8.3, 5 years), and it continues to be the Q1 area among the four subject classifications. Nano Research Award, established by Nano Research together with TUP and Springer Nature in 2013, and Nano Research Young Innovators (NR45) Awards, established by Nano Research in 2018, have become international academic awards with global influence.
Nano Research
Engineering optoelectronic properties of two-dimensional transition metal dichalcogenides via acid treatment: defect manipulation mechanisms and the optical–electrical trade-off
5-Aug-2026