(Nanowerk Spotlight) The screen on your smartphone or television contains millions of tiny light-emitting elements that activate individually to create images. Current display technologies use either organic molecules (OLEDs) or semiconductor nanocrystals called quantum dots (QD-LEDs) to generate this light. While these technologies produce vibrant colors, they operate at efficiencies far below their theoretical potential due to a fundamental electrical mismatch: the electrons and positively charged “holes” that must combine to create light move at different speeds through the display materials.
This mismatch creates several problems. In QD-LEDs, some electrons pass through the quantum dot layer without encountering a hole, wasting energy. Others recombine inefficiently, releasing heat instead of light through a process called Auger recombination. These inefficiencies limit brightness, reduce battery life in portable devices, and ultimately cause displays to degrade more quickly.
Scientists have explored various solutions to address these issues. One alternative, quantum-dot light-emitting electrochemical cells (QD-LECs), incorporates mobile ions to improve charge transport. However, these devices lack critical charge-containment structures, leading to poor efficiency (below 1%) and short operational lifetimes.
Recent advances in understanding how ions interact with electrons at material interfaces have opened new possibilities. By precisely engineering the movement of charged particles at the nanoscale, researchers are finding ways to overcome limitations that have persisted in display technology for decades.
Researchers from Sun Yat-sen University and Zhejiang University have now developed a display technology that significantly improves efficiency and longevity. Their research, published in Advanced Materials (“Quantum-Dot-Electrolyte Light-Emitting Diodes for Displays”), introduces quantum-dot-electrolyte LEDs (QE-LEDs), which incorporate ionic liquids directly into the light-emitting layer.
“We report another class of EL devices, which is called QD-electrolyte LED,” the researchers explain. “The key feature of QE-LED is that an ionic liquid is doped into QDs as the electrolyte emitter.”
This approach differs fundamentally from existing technologies. Unlike conventional QD-LEDs, QE-LEDs contain mobile ions that enhance charge flow. Unlike QD-LECs, they maintain a structured multilayer architecture that properly balances and contains the charged particles.
Schematic structure of QE-LEDs and emission mechanisms. a) Overview of the QE-LED structure, comprising an organic HTL/inorganic electronic transport layer (ETL) hybrid structure with a QD-electrolyte EML. Molecular structure of the ionic liquid (THA-BF4) utilized in the QD-electrolyte layer. b) Detailed magnification of the selected region in Figure 1a, illustrating the crosslinked TFB/QD-electrolyte/ZnMgO interface and the mechanistic analysis of charge behavior at the ZnMgO/QD-electrolyte layer/TFB interface. c) Schematic of the EDL model for ion distributions near the ZnMgO thin film. The diffuse layer is induced by the electrical double layer (EDL). (Image: Reprinted with permission by Wiley-VCH Verlag) (click on image to enlarge)
The team used tetrahexylammonium tetrafluoroborate (THA-BF4), an ionic liquid that dissolves well in the same solvents used for quantum dots. When voltage is applied, the positive and negative ions migrate toward opposite electrodes, forming electrical double layers (EDLs)—microscopically thin regions of separated charge—at material interfaces.
These EDLs act like molecular charge pumps, creating intense electric fields that significantly improve how efficiently electrons and holes enter and move through the quantum dots. Using scanning Kelvin probe microscopy, the researchers directly measured these enhanced fields.
The performance improvements are substantial. At 5.0V, QE-LEDs produced three times more light than standard QD-LEDs and forty times more than QD-LECs. The devices reached a maximum brightness of 58,692 cd/m² with an external quantum efficiency (EQE) of 17.0% at 3.0V, surpassing conventional designs.
However, the initial QE-LEDs suffered from electron overflow, where excess electrons passed through the quantum dots without producing light. To address this, the researchers added a small amount of polymethyl methacrylate (PMMA), an insulating polymer, to the quantum-dot-electrolyte mixture.
This addition selectively reduced excess electron flow, improving the ratio of electrons to holes in the quantum dots. The optimized devices achieved an EQE of 20.5%, matching the best OLED and QD-LED technologies while consuming less power.
Beyond efficiency, QE-LEDs demonstrated remarkable longevity. The optimized devices maintained 95% of their initial brightness for a projected 374,000 hours (over 42 years) at standard display brightness (100 cd/m²). While few electronic devices remain in use for decades, this translates to displays that maintain consistent brightness throughout their lifespan without the gradual dimming seen in current technologies.
To validate real-world applicability, the researchers fabricated active-matrix displays by integrating QE-LEDs with the thin-film transistor (TFT) backplanes used in commercial products. These displays showed uniform emission and stable performance after 400 hours of continuous operation at high brightness levels. The technology also supports refresh rates above 1,000 Hz, far exceeding the 60-120 Hz of most current displays. This improvement allows smoother motion rendering for applications such as gaming and virtual reality.
“The QE-LED is among the best EL devices,” the researchers note. “Furthermore, an active-matrix QE-LED display is demonstrated with superior stability that overtakes the commercial benchmark.”
Detailed measurements confirmed that adding ionic liquid and PMMA preserved the optical quality of the quantum dots. The photoluminescence quantum yield remained at approximately 75%, and the emission wavelength stayed centered at 622 nanometers with a narrow spectral width, ensuring precise color reproduction.
To further understand the ionic enhancements, the researchers used impedance spectroscopy, which revealed that QE-LED films have significantly lower electrical resistance (24 Ω vs. 68 Ω for standard QD films). Theoretical simulations showed that the electrical double layers improved charge tunneling probabilities at material interfaces by orders of magnitude.
This hybrid approach simultaneously solves multiple problems. Ionic liquids enhance charge injection and transport, while PMMA improves charge balance within the quantum dots. The multilayer structure ensures efficient charge containment, maximizing light emission.
While the study focused on display applications, the principles demonstrated in QE-LEDs could extend to other optoelectronic devices, including lighting panels, optical communication systems, photodetectors, and solar cells.
By addressing fundamental limitations in charge transport and recombination, this work highlights how materials engineering can overcome persistent challenges in light-emitting devices. The combination of high efficiency, extended operational lifetime, and compatibility with existing manufacturing techniques positions QE-LEDs as a promising technology for next-generation displays that deliver brighter visuals with improved energy efficiency.
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
