A new study has examined how structural and chemical changes contribute to the degradation of heavy-metal-free quantum dot light-emitting diodes (QD-LEDs) during operation. The researchers studied the structural and chemical changes that occur inside red and blue cadmium-free QD-LEDs as they age under electrical stress. The study highlights acrylate-based resin encapsulation as a practical solution for extending the operational lifetime of QD-LEDs.
Study: Morphological and chemical changes in Cd-free colloidal QD-LEDs during operation. Image Credit: BokehStore/Shutterstock.com
Addressing the Stability Challenges of Cadmium-Free QD-LEDs
QD-LEDs deliver high brightness, excellent color purity, and are compatible with flexible electronic devices.
Although red and green QD-LEDs have achieved high efficiencies, heavy-metal-free devices based on indium phosphide (InP) and zinc telluride selenide (ZnTeSe) still suffer from limited operational lifetimes. This durability challenge remains a major obstacle to their commercial adoption.
Earlier research has focused on improving device efficiency by optimizing QDs, charge transport layers, and overall device architecture. However, researchers have paid very little attention to the physical and chemical changes that occur inside QD-LEDs during operation. While electrical stress was known to reduce device performance over time, the underlying degradation mechanisms remained poorly understood.
In this study, researchers investigated how the structure and chemical composition of cadmium-free QD-LEDs change during operation. They compared red InP/ZnSe/ZnS and blue ZnTeSe/ZnSe/ZnS devices before and after electrical aging. The study also showed that remote acrylate-based resin encapsulation suppresses these degradation processes, significantly improving device stability and extending operational lifetime.
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Combining Advanced Microscopy with Chemical Mapping
The researchers fabricated red and blue cadmium-free QD-LEDs using indium tin oxide electrodes, charge transport layers, QD emissive layers, ZnMgO electron transport layers, and aluminum electrodes. They coated some devices with a remote acrylate-based resin, while leaving others uncoated for comparison during aging tests.
The team operated the devices under a constant current until the brightness dropped to half of its initial value. Then, they compared pristine and aged devices using high-resolution transmission electron microscopy (TEM). To accurately quantify structural changes, the team also developed an image-processing algorithm that measured variations in the thickness of individual device layers.
The researchers utilized energy-dispersive X-ray spectroscopy (EDS) to monitor oxygen migration and time-of-flight secondary ion mass spectrometry (TOF-SIMS) to map the distribution of hydrogen and oxygen within the devices. Thermal simulations showed that self-heating remained minimal during operation, indicating that temperature was not the primary driver of degradation.
The team performed in situ environmental TEM experiments on ZnMgO nanoparticle films to better understand the degradation process. They exposed the films to hydrogen, oxygen, and water vapor under controlled conditions and observed how each environment affected nanoparticle stability. These techniques helped the team to distinguish structural changes from electrical effects and identify the chemical species responsible for device degradation.
Structural Rearrangement Drives Device Degradation
The analysis revealed that prolonged operation caused significant structural changes in both red and blue cadmium-free QD-LEDs. TEM images showed that the QD and ZnMgO electron transport layers gradually became thinner and denser as the devices aged. At the same time, individual nanoparticles grew larger, interfaces became less distinct, and the layered structure began to deteriorate. These changes disrupted charge transport and increased energy losses, reducing overall device performance.
Chemical analysis provided further evidence of the degradation process. Oxygen accumulated at the interface between the aluminum electrode and the ZnMgO layer before migrating into the QD layer in aged, uncoated red devices. Hydrogen also accumulated at several interfaces, confirming that electrical operation drives elemental migration throughout the device. Together, these structural and chemical changes accelerated device degradation.
The in-situ TEM experiments identified hydrogen as a key contributor to this process. Hydrogen exposure rapidly caused ZnMgO nanoparticles to coarsen, whereas oxygen and water produced little structural change. Under the same conditions, the QDs remained largely unchanged. This finding indicates that degradation begins primarily in the ZnMgO electron transport layer rather than in the emissive QDs.
The acrylate-based resin significantly improved device stability. Resin-coated devices maintained their original layer thickness, showed much less oxygen and hydrogen migration, and largely avoided nanoparticle coarsening. As a result, the projected operational lifetime increased by more than 50-fold for red InP devices and over 5,000-fold for blue ZnTeSe devices without sacrificing external quantum efficiency. These findings show that controlling nanoscale structural changes is critical for building durable QD-LEDs.
Toward Durable and Commercially Viable QD Displays
This study provides new insights into how heavy-metal-free QD-LEDs lose performance during operation. The researchers show that failure results from a combination of nanoparticle coarsening, layer thinning, and the migration of oxygen and hydrogen across the device. Improving long-term stability therefore requires controlling both the device structure and its chemical environment.
The acrylate-based resin offers a practical solution to this challenge. The resin protects the device by limiting elemental migration, suppressing chemical activity, and preserving critical functional layers. This simple encapsulation strategy substantially improves reliability without requiring major changes to the device architecture.
The findings provide valuable design insights for next-generation optoelectronic devices based on multilayer nanostructures. Understanding how these interfaces evolve during operation can improve material stability, enhance charge transport, and extend device lifetime. As cadmium-free QD-LEDs move closer to commercialization, controlling both morphology and chemistry will be critical for developing efficient, durable, and environmentally friendly display technologies.
Journal Reference
Zhang, R., Geng, J., et al. (2026). Morphological and chemical changes in Cd-free colloidal QD-LEDs during operation. Science Advances, 12(28). https://www.science.org/doi/10.1126/sciadv.aec8208
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