The device is based on silver bismuth sulfide, or AgBiS₂, colloidal quantum dots. These nanoscale semiconductor particles have attracted attention because they absorb light efficiently across a broad spectral range and can be processed from solution, offering a potentially lower-cost alternative to conventional semiconductor fabrication. Unlike many high-performance infrared quantum dots based on lead or mercury, AgBiS₂ avoids the most serious toxicity concerns associated with heavy-metal materials. Yet its practical performance has been limited by a difficult interface problem inside the detector.

A photodetector works by converting incoming photons into mobile electrical charges. In an AgBiS₂ device, the photoactive quantum-dot layer must transfer electrons efficiently into an electron transport layer, which then carries them toward an electrode. If the energy levels at that boundary are poorly aligned, electrons can become trapped or recombine with holes before they are collected. The same defects can also allow unwanted current to flow in darkness. This dark current acts like electronic background noise, making it difficult to distinguish a weak optical signal from the detector’s own electrical activity.

To solve this problem, a research team led by Professors Bingkun Chen and Guohui Li introduced a bilayer electron transport structure made from zinc oxide and MXene. Rather than relying on a single transport material, the researchers used the two layers to engineer the interface between the quantum dots and the device’s charge-collecting components. Their design improves energy-level alignment, reduces interfacial defects, and creates a more favorable route for photogenerated electrons. The result is a detector designed to collect useful charges while blocking unnecessary current injection.

The performance numbers are striking. The optimized device achieved a dark-current density of just 6.1 × 10⁻⁸ amperes per square centimeter, reported as the lowest value so far for an AgBiS₂ colloidal quantum-dot photodetector. It responded to light from 375 to 1120 nanometers, spanning much of the visible spectrum and extending well into the near-infrared. At a wavelength of 980 nanometers, its specific detectivity reached 7.8 × 10¹⁰ Jones, a standard measure of how effectively a detector can identify weak radiation in the presence of noise.

The detector also delivered a linear dynamic range of 80 decibels. This value describes how wide a range of light intensities the device can measure while maintaining a predictable relationship between illumination and electrical output. A broad linear range is particularly important in imaging, where a single scene may contain both brightly illuminated and extremely dim regions. Compared with devices using traditional single-layer electron transport structures, the bilayer detector improved detectivity by approximately 3.5 to seven times, according to the research team.

The improvement is linked to the way the ZnO/MXene combination manages charge at the nanoscale. Zinc oxide provides an electron-transporting semiconductor interface, while the MXene layer helps modify the electronic environment and facilitate charge movement. Together, the layers reduce the barrier that electrons encounter as they leave the AgBiS₂ quantum dots. They also help passivate imperfections at the interface, limiting the pathways through which charges can disappear or unwanted carriers can enter. In practical terms, this means a stronger signal with less background interference.

To test whether the laboratory results could translate into imaging, the researchers integrated the photodetector with a 64 × 64 thin-film-transistor array. The resulting system produced clear and stable near-infrared images at 850 nanometers. This demonstration matters because an individual detector can show impressive sensitivity without necessarily functioning well in a large array. Uniformity, stability, and compatibility with electronic readout circuits are all essential for cameras and sensor platforms. The successful array experiment suggests that the architecture may be suitable for scalable imaging technologies rather than remaining a proof-of-concept material study.

The researchers describe the work as an interface-engineering strategy that could extend beyond AgBiS₂. By controlling energy alignment and defect-related losses at the boundary between quantum dots and transport layers, similar methods could help improve other lead-free optoelectronic devices. Potential applications include low-light imaging, wearable biomedical sensors, machine vision, environmental monitoring, and optical communication systems. The study, published in Nano Research on June 25, 2026, presents the ZnO/MXene bilayer as a route toward near-infrared sensors that combine high sensitivity, low dark current, solution-processable materials, and reduced reliance on toxic elements.

Subject of Research: Lead-free AgBiS₂ colloidal quantum-dot near-infrared photodetector using a ZnO/MXene bilayer electron transport layer

Article Title: ZnO/MXene bilayer electron transport layer enables ultra-low dark current AgBiS₂ quantum dot near-infrared photodetector for high-performance imaging

News Publication Date: 25 June 2026

Web References: https://doi.org/10.26599/NR.2026.94908699; Nano Research

References: Nano Research, DOI: 10.26599/NR.2026.94908699

Image Credits: Nano Research, Tsinghua University Press

Keywords

AgBiS₂ quantum dots, MXene, zinc oxide, near-infrared photodetector, quantum-dot imaging, lead-free optoelectronics, dark current, detectivity, thin-film-transistor array, nanotechnology

The research team’s approach employed a sophisticated method known as high-temperature successive ion layer adsorption and reaction (HT-SILAR). By utilizing this technique, researchers have synthesized a new class of gradient alloyed quantum dots that offer significant improvements in luminescent properties. The tailored QDs composed of a composite structure of CdZnSe/Zn₁₋ₓCdₓSe/ZnSe/ZnS/CdZnS exhibit an impressive ultra-narrow emission full width at half maximum (FWHM) of just 17.1 nm. This characteristic is remarkable and contributes significantly to the high color purity of the emitted light.

The photoluminescence quantum yield (PLQY) of these QDs is near unity, indicating that they can convert nearly all absorbed light into emitted light with minimal losses. As a result, the external quantum efficiency (EQE) of the red QLEDs reached a record-breaking 38.2%. This exceptional efficiency suggests that not only can these devices output brilliant color, but they can also do so while consuming less power, a vital characteristic for sustainable technology.

Furthermore, the operational lifetime of the devices tested at a luminance level of 1,000 cd/m² exceeds 24,100 hours. This impressive stability ensures that these QLEDs can maintain top performance for extended periods, making them a reliable choice for consumers. To put this into perspective, if these devices are utilized for eight hours per day, they could last for up to eight years without significant degradation in performance. The ability to sustain long-term brightness and efficiency is a game-changer for manufacturers and end-users alike.

The synthesis process involved meticulous control over the thickness of the Zn₁₋ₓCdₓSe/ZnSe shells, which effectively alleviates compressive strain within the quantum dots. This strain reduction is crucial, as it prevents the heavy-hole energy band splitting and weakens exciton-phonon coupling—two phenomena that negatively impact luminescence. By mastering this control, the researchers have made strides in enhancing the quality and performance of the QDs.

Another critical aspect of the research is the design of the shell layers. The advanced configuration of the Zn₁₋ₓCdₓSe/ZnSe/ZnS shells confines electronic carriers within the core of the quantum dots. This design tweak enhances the efficiency of light emission by boosting PLQY. In addition, the incorporation of Cd-doped ZnS shells acts to passivate surface defects, facilitating smooth hole injection and achieving balanced carrier recombination. This control translates into devices that do not merely operate effectively on paper but exhibit real-world performance improvements and stability.

Further findings reveal that the use of large-size quantum dots significantly reduces heat generation in the QLED devices. This is an essential factor since excessive heat can lead to detrimental effects, such as screen burn-in, which affects image quality and longevity. By mitigating this risk, the research team has also addressed a common issue in existing display technologies, thus bolstering user satisfaction and device reliability.

As investigations into these novel QDs continue, they serve as a foundation for the advancement of display technologies designed to meet high consumer expectations. The breakthrough is not only significant for devices like televisions and monitors but also sets the stage for more sophisticated applications in various fields, including medical imaging and advanced lighting solutions. As manufacturers look for greener and more tech-savvy ways to provide vibrant displays, these findings hold great promise for the future of the industry.

The research was published in the peer-reviewed journal "Science Bulletin," highlighting its significance in the scientific community. The findings and techniques outlined in the publication are expected to attract considerable attention from both academia and industry sectors alike, as they pave the way for next-generation optoelectronic devices.

Moreover, the collaborative nature of this research unites institutions known for their expertise in materials science and engineering, further enhancing the credibility and reach of the study. The results showcase the importance of interdisciplinary approaches to tackle complex scientific challenges.

With the groundbreaking results and the potential impact of these large-particle quantum dots on the QLED landscape, this study opens exciting avenues for future exploration. As QLED technology continues to evolve, it is crucial to monitor further developments in quantum dot synthesis and device architecture that could result in even greater efficiencies and capabilities.

In conclusion, the advancements made by the Soochow University and Macau University of Science and Technology demonstrate significant strides in quantum dot technology that can bring forth innovations in both consumer electronics and material science sectors. The implications of this research stretch far beyond the confines of academia, promising a bright future for display technologies that harness the true potential of quantum dots.

Subject of Research: Quantum Dot Light Emitting Diodes
Article Title: Advancements in Quantum Dot Technology Enhancing QLED Performance
News Publication Date: October 2023
Web References: Science Bulletin DOI
References: Science Bulletin, Soochow University Research
Image Credits: ©Science China Press

Keywords

Quantum dots, QLEDs, photoluminescence, external quantum efficiency, stability, display technology, high-temperature successive ion layer adsorption and reaction, materials science, optoelectronics, luminescent materials, quantum efficiency, surface defects.