New technology for eco-friendly blue LEDs without toxic metals

Very few people know that although the sharp, electric blue glow in today's best screens looks effortless, it's actually one of the hardest colors scientists have ever tried to perfect. Deep-blue light is essential for the vivid full-color spectrum of modern screens and efficient lighting, but making it safely, sustainably, and affordably has been a long-standing challenge.

Now, a research team from Rutgers University, the U.S. Department of Energy's National Renewable Energy Laboratory (NREL), Shenzhen Polytechnic University, the University of North Texas, and national labs like Brookhaven and Lawrence Berkeley, has found what could be a solution. Their study, published in Nature, introduces a copper–iodide hybrid material that emits a brilliant deep-blue light, without relying on toxic metals like lead or cadmium.

And the improvement is significant: near-perfect light emission efficiency (99.6%), stable color at 449 nanometers, and a record-breaking external quantum efficiency (EQE) of 12.6% in prototype LEDs. All of that from a material that's cheap, abundant, and environmentally friendly.

Creating a good blue LED is like trying to make a fire that burns cool and bright at the same time, it's inherently difficult. Red and green emitters are relatively easy, but blue requires materials that can handle higher energy photons without breaking down. Historically, scientists have turned to lead-based perovskites or cadmium quantum dots for their efficiency, but those come with toxicity and stability issues.

Displays and lighting consume an enormous amount of energy worldwide. Even small improvements in efficiency can ripple out into huge savings. But environmental safety is just as crucial. Blue organic LEDs tend to fade quickly, and the safer alternatives, like indium-based compounds, are costly and complex to manufacture. As the researchers put it, there's been an "urgent need" for a cost-effective, non-toxic, and stable blue-emitting material.

That's where copper–iodide hybrids come in.x

Copper and iodine may sound humble compared to exotic rare-earth elements, but in the hands of materials scientists, they can do something extraordinary. These compounds are non-toxic, abundant, and resilient in air and moisture, qualities that make them ideal for scalable light-emitting devices.

Earlier attempts using copper–iodide clusters showed promise but suffered from inefficiencies when used in actual LEDs. The problem was at the interfaces, the delicate regions where different layers of the device meet and where electrical charges can get stuck, wasted, or trapped.

So, the research team attacked that problem from two sides, literally. In fact, their innovation centers on what they call a "dual interfacial hydrogen-bonding passivation" strategy. Yes, it's a mouthful, but the idea is simple: use the gentle "Velcro" of chemistry, hydrogen bonds, to make the layers of the LED stick together more smoothly.

In a typical LED, you have multiple layers: one that injects positive charges (holes), one that injects negative charges (electrons), and the middle "emissive layer" that actually glows when those charges meet. Any roughness or chemical mismatch between layers can cause defects, leading to wasted energy and shorter lifetimes.

So the researchers added two special coatings. A self-assembled monolayer (SAM) that bonds to the hole-transport side, and an ultrathin polymer (PMMA) capping layer that hugs the electron-transport side.

Both act as hydrogen-bond acceptors, passivating (smoothing out) surface defects and optimizing how charges flow in and out of the light-emitting layer. The result is a remarkably stable interface, like giving your LED the world's most supportive handshake from both sides.

At the heart of the breakthrough is a hybrid compound called CuI(Hda). The scientists designed this hybrid so that copper and iodine atoms form a one-dimensional chain, with organic molecules acting as connectors and stabilizers.

Under ultraviolet light, these crystals glow a vivid blue. When processed into thin films, they remain exceptionally smooth, just 0.18 nanometers rough on average, almost atomically flat. That uniformity helps the LEDs emit light efficiently and consistently.

Even more intriguing is how CuI(Hda) produces its light. Most materials emit through a single process, fluorescence or phosphorescence. But this one combines three pathways: rapid fluorescence, delayed fluorescence (a thermally activated version), and phosphorescence. This "triple play" of emission channels is one reason the material can reach near-perfect luminescence efficiency.

The researchers' deep-blue LED prototypes used CuI(Hda) as the only active light-emitting layer, which simplifies manufacturing. The devices reached a maximum brightness of nearly 4,000 candela per square meter, plenty for display applications, and held their color steady even under stress.

The dual hydrogen-bonding treatment (or DIHP, as the paper calls it) boosted efficiency by more than fourfold compared to untreated devices. Their EQE of 12.57%, meaning over one in ten electrons becomes a photon, is a record for copper-based deep-blue LEDs and competitive with commercial perovskite technologies, minus the lead.

Even better, the devices proved stable, continuing to shine for over 200 hours under continuous operation in open air, something few blue-emitting materials can manage. And they scaled it up: a 4-square-centimeter LED panel maintained high efficiency across its surface, showing the method could be practical for larger displays.

By showing that earth-abundant, non-toxic materials like copper and iodine can compete with the best commercial emitters, this research could shift how we design the next generation of displays and solid-state lighting.

Moreover, the hydrogen-bond engineering approach offers a universal trick: the same principle might enhance perovskites, organic LEDs, or other hybrid semiconductors. Hydrogen bonds, after all, are the quiet glue of the molecular world, strong enough to hold DNA together, now strong enough to hold an LED at peak performance.

The next steps will focus on pushing the material's operational lifetime further, beyond hundreds to thousands of hours, and integrating it into flexible or transparent devices. Given its excellent stability in air and moisture, CuI(Hda) could one day power eco-friendly displays, wearable electronics, or even next-generation lighting that mimics daylight with stunning accuracy.

If you want to learn more, read the original article titled "Dual interfacial H-bonding-enhanced deep blue hybrid copper–iodide" on Nature at http://dx.doi.org/10.1038/s41586-025-09257-8.