The 1550-nanometre band occupies a particularly valuable position in the near-infrared spectrum. Light at this wavelength is widely used in optical communications, while also offering practical advantages for sensing systems that must operate around people, vehicles and other sensitive environments. Compared with shorter-wavelength lidar sources, 1550-nanometre systems can be designed to meet eye-safety requirements at higher transmitted energies under appropriate operating conditions. Greater permissible pulse energy can translate into stronger returning signals, longer useful sensing distances or improved performance when atmospheric conditions weaken the reflected light. Yet detecting this wavelength efficiently and selectively remains a demanding engineering problem, especially when lidar hardware must become smaller, cheaper and more power-conscious.

The central idea in the new work is to use colloidal quantum dots as the light-absorbing material in a tandem photodiode. Colloidal quantum dots are semiconductor nanocrystals whose optical and electronic properties can be tuned by controlling their composition, size and surface chemistry. Unlike many conventional semiconductor detector materials, they can be deposited from inks and processed over relatively large areas using techniques compatible with low-temperature fabrication. Their absorption can also be adjusted across the visible and infrared spectrum, making them attractive for sensors that must be tailored to a specific wavelength. In a tandem device, multiple quantum-dot photodiodes are placed in a vertical stack, allowing the structure to interact with incoming light in a controlled, wavelength-dependent manner.

Spectral selectivity is essential because a lidar detector does not receive only the signal sent by its laser. Sunlight, artificial lighting, reflections from nearby objects and electronic noise can all contribute unwanted background. If a detector responds broadly across the spectrum, the desired return pulse may be buried beneath those competing signals. A spectrally selective detector instead acts like an optical and electronic gate: it preferentially responds to the target wavelength while suppressing light outside the sensing band. By integrating two photodiode sections rather than relying on a single absorbing layer, the tandem architecture gives researchers additional freedom to shape how different wavelengths are absorbed, transmitted or converted into electrical signals.

In operation, a lidar transmitter emits light toward a target, and the reflected photons travel back to the receiver. The detector converts those photons into an electrical response, while timing electronics determine the interval between transmission and return. Because light travels at a fixed speed, even a very short delay contains information about distance. The challenge becomes more severe as targets grow darker, farther away or partially obscured by haze, because fewer photons return to the detector. A detector designed specifically for 1550 nanometres can improve the ratio between the useful lidar signal and the surrounding optical background. The tandem quantum-dot structure is therefore not simply a new material choice; it is an attempt to unite wavelength control, photodetection and lidar-specific signal processing in one integrated platform.

The use of colloidal quantum dots could also change how future lidar receivers are manufactured. Traditional infrared photodiodes often depend on specialized semiconductor growth, high-temperature processing or costly substrates. Quantum-dot layers, by contrast, can potentially be deposited on diverse surfaces and incorporated into thin, lightweight devices. That flexibility is especially relevant for emerging lidar systems in robotics, drones, industrial monitoring and vehicles, where bulky optical assemblies can limit design options. A detector that is compact and spectrally targeted could help reduce the burden placed on filtering optics, cooling systems and downstream computation. It may also open routes toward detector arrays capable of combining distance information with wavelength-sensitive imaging.

The concept is significant because lidar is moving from laboratories and high-end surveying equipment into everyday machines. Autonomous vehicles need to distinguish road users, barriers and road geometry under changing illumination. Robots must navigate warehouses, factories and homes filled with reflective and irregular surfaces. Atmospheric and environmental instruments use laser ranging to study aerosols, vegetation and changing landscapes. In each of these applications, the receiver must separate a deliberately generated optical signal from a complex background. Spectral selectivity can provide an additional layer of discrimination before the data reaches software, potentially reducing the amount of information that must be filtered digitally and improving the reliability of measurements made in bright or optically cluttered environments.

The reported platform also highlights a broader shift in photonics: the effort to build sophisticated optical functions directly into thin-film semiconductor devices. Instead of treating the detector as a passive endpoint connected to a separate collection of filters and optical components, researchers are increasingly designing the material stack itself to perform part of the signal-selection task. Tandem quantum-dot photodiodes fit this philosophy because their individual layers can be engineered to absorb different portions of the spectrum and to work together electrically. Such control may eventually support receivers that are not only sensitive at 1550 nanometres but can also distinguish multiple bands, identify atmospheric interference or combine ranging with chemical and material recognition.

Important questions remain before the technology can become a commercial lidar component. Practical systems must maintain stable performance over temperature changes, prolonged illumination and repeated electrical operation. Quantum-dot surfaces require careful chemical treatment because defects and imperfect interfaces can trap charge, slow the detector response or increase noise. A lidar receiver must also balance sensitivity against speed: detecting very weak signals is useful only if the device can respond quickly enough for high-rate ranging. Manufacturing uniform tandem stacks over large areas, protecting them from moisture and oxygen, and integrating them with readout electronics are additional challenges. The new study places spectral-selective quantum-dot detection into a lidar context, but the wider path to deployment will depend on how the devices perform under the demanding conditions of field operation.

Even with those challenges, the research points toward a future in which lidar receivers are designed around the physics of the signal they need to measure. The 1550-nanometre wavelength is already central to optical communications and advanced ranging, but its full potential depends on detectors that can recognize it efficiently amid a flood of unwanted light. By combining tunable colloidal quantum dots with a tandem photodiode structure, the researchers offer a route to make that recognition more precise and potentially more manufacturable. If the approach can be refined for speed, durability and scalable production, it could contribute to a new generation of selective lidar systems—devices that see farther not merely by transmitting more light, but by becoming smarter about which photons count.

Subject of Research: Spectral-selective 1550-nanometre light detection and ranging using tandem colloidal quantum dot photodiodes.

Article Title: Spectral-selective light detection and ranging at 1550 nm using tandem colloidal quantum dot photodiodes.

Article References: Yang, J., Liu, J., Deng, C. et al. “Spectral-selective light detection and ranging at 1550 nm using tandem colloidal quantum dot photodiodes.” Light Science & Applications 15, 355 (2026). https://doi.org/10.1038/s41377-026-02244-2

Image Credits: AI Generated

DOI: https://doi.org/10.1038/s41377-026-02244-2

Keywords: lidar, light detection and ranging, 1550 nm, colloidal quantum dots, tandem photodiodes, spectral-selective detection, near-infrared photodetectors, optical sensing, photonics, autonomous systems.

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