Common Polymer additive Boosts Quantum-Dot LED Efficiency with a Simple Surface Treatment

A dash of an everyday polymer may be all it takes to squeeze more light out of quantum-dot light-emitting diodes. In a study published in the Journal of Materials Science, a team of researchers from Phenikaa University, VNU University of Engineering and Technology, and the Vietnam Academy of Science and Technology reports that treating the emissive region of CdSe/ZnS quantum-dot LEDs with polyethylene glycol, better known as PEG, substantially improves how efficiently injected electrical current is converted into visible light. The work, led by Huu Tuan Nguyen of Phenikaa University, offers a low-cost, solution-based route to better quantum-dot displays without redesigning the entire device stack.

Quantum-dot LEDs, or QLEDs, are among the most promising technologies for next-generation displays because the nanoscale semiconductor crystals at their heart emit extremely pure, tunable colors. In the devices studied here, the light-emitting layer consists of cadmium selenide cores wrapped in zinc sulfide shells, sandwiched between charge-transport layers that steer electrons and holes toward the dots. When the two types of charge meet inside a quantum dot, they can recombine radiatively and emit a photon, or they can be lost through non-radiative pathways and defects. The fraction of current that ends up as light, rather than heat or leakage, is what determines a display’s brightness and energy efficiency, and it is precisely the quantity the Vietnamese team set out to improve.

The researchers’ strategy targeted the interface between the hole-transport polymer poly-TPD and the quantum-dot layer, a region widely recognized as a bottleneck in these devices. By applying a PEG-assisted modification to this poly-TPD/QD region, they altered the physical and electrical character of the junction where holes are injected into the emissive layer. Compared with an otherwise identical untreated device, the PEG-treated QLED showed a lower current density at a given voltage together with higher luminance, higher current efficiency, and higher external quantum efficiency. Taken together, those trends point to a cleaner conversion of injected current into photons: less current flows, but more of what does flow produces light.

The headline numbers are striking for such a simple intervention. The maximum luminance of the treated devices increased by approximately 1.8-fold, while the maximum current efficiency rose by approximately 1.6-fold. In practical terms, the modified LEDs could be driven roughly twice as bright, and every milliamp of current delivered roughly sixty percent more light. For display manufacturers, improvements of this magnitude achieved through a solution-processable additive, rather than new materials or vacuum deposition steps, are exactly the kind of incremental engineering that compounds into commercially meaningful gains.

To understand where the improvement came from, the team examined the surface quality of the deposited quantum-dot films using atomic force microscopy. The measurements revealed a decrease in the root-mean-square roughness of the film from 1.367 nanometers to 0.829 nanometers after PEG treatment, even though the overall topographical features remained qualitatively similar. That smoothing matters because rough, uneven films create local thickness variations and poorly contacted regions where charge can accumulate, leak, or recombine without emitting. A flatter emissive layer promotes more uniform current spreading and more consistent contact between the quantum dots and the adjacent transport layers, which is consistent with the improved current-to-light conversion the team observed.

The electrical analysis went beyond simple current-voltage curves. The researchers fitted the forward-bias current density-voltage characteristics using a modified Shockley-type expression, a phenomenological device-level model borrowed from classical diode physics and adapted for the layered reality of QLEDs. Two extracted parameters proved especially informative: the effective ideality factor, which describes how far the device departs from ideal diode behavior, and the current prefactor, which sets the overall scale of the current response. PEG treatment produced lower values of both parameters, alongside a higher effective series resistance.

The authors are notably careful about what these fitted parameters do and do not mean. They emphasize that the ideality factor and prefactor describe the aggregate non-ideal electrical response of the entire multilayer device and should not be interpreted as direct measurements of leakage current, trap density, or non-radiative recombination. That restraint is a welcome corrective to a common pitfall in the LED literature, where ideality factors are often over-interpreted as clean probes of specific loss mechanisms. In a device with many stacked layers and interfaces, a single diode equation can only summarize the combined behavior, and the Vietnamese team frames their findings accordingly, discussing the performance enhancement as a correlation among PEG treatment, surface topography, and device-level charge transport rather than claiming a single microscopic cause.

The higher effective series resistance in the treated devices fits naturally with the observed lower current density. PEG, an insulating polymer, appears to moderate the flow of charge through the modified region, suppressing parasitic current paths that consume current without generating light. The trade-off is favorable: the modest additional resistance costs some current, but the current that remains is used far more productively in the emissive dots. This echoes a recurring theme in quantum-dot optoelectronics, where the goal is not to maximize current but to balance electron and hole injection so that charges meet and recombine where they should.

PEG itself is an intriguing choice of additive. The inexpensive, water-soluble polymer has a track record in organic and hybrid electronics, where it has been used to modify the conductivity of PEDOT:PSS electrodes and to passivate zinc oxide electron-transport layers in blue quantum-dot LEDs. Its ether-linked oxygen atoms can coordinate to surface sites and its polymer chains can mediate film morphology, making it a versatile interfacial agent. The new study extends this toolkit to the poly-TPD/quantum-dot interface in CdSe/ZnS devices, showing that the same benign chemistry can smooth films and reshape charge transport in a full LED stack.

The work was supported by the National Foundation for Science and Technology Development of Vietnam under Project 103.03-2023.80, and the authors state that the data supporting the findings are available within the article. While Cd-based quantum dots face regulatory scrutiny in consumer products, the interfacial modification strategy demonstrated here is material-agnostic in principle and could transfer to cadmium-free emitters such as the InP-based dots now driving commercial development. For a field chasing every last percent of efficiency, the message of this study is refreshingly simple: sometimes the biggest gains come not from new nanocrystals, but from treating the surfaces you already have with a polymer you can buy by the bottle.

Subject of Research: PEG-assisted interfacial modification for improved efficiency of CdSe/ZnS quantum-dot light-emitting diodes

Article Title: Improved current-to-light conversion in CdSe/ZnS quantum-dot light-emitting diodes through PEG-assisted interfacial modification

Article References: Nguyen, H. T., Duong, A. T., Van Hoang, N., Nguyen, D. L., & Nguyen, T. H. (2026). Improved current-to-light conversion in CdSe/ZnS quantum-dot light-emitting diodes through PEG-assisted interfacial modification. Journal of Materials Science. https://doi.org/10.1007/s10853-026-13950-y

Image Credits: AI Generated

DOI: 10.1007/s10853-026-13950-y

Keywords: quantum dots, QLED, CdSe/ZnS, polyethylene glycol, PEG, poly-TPD, external quantum efficiency, atomic force microscopy, ideality factor, charge transport, interfacial modification, display technology