Chemists boost efficiency of hybrid LEDs to nearly 40 percent

Researchers at Emory University have developed a method to significantly improve the efficiency of light-emitting diodes (LEDs) made from perovskite materials. By refining the chemical process used to manufacture the devices, the team achieved a quantum efficiency of up to 37 percent, compared with the 20 to 30 percent typically reported in previous research.

The findings, published in the journal Nature, could help advance the development of lightweight, flexible and cost-effective LEDs for applications including biomedical imaging, low-light photography and facial recognition.

The research was led by Letian Dou, professor of chemistry at Emory University. His team investigates hybrid LEDs made from metal-halide perovskites, materials that combine organic and inorganic components. These devices could offer a combination of flexibility, efficiency and relatively low manufacturing costs.

Conventional LEDs based on inorganic semiconductors, such as gallium nitride, are efficient, durable and long-lasting. However, their rigid structure can make them difficult to integrate into flexible devices or manufacture as extremely small pixels. Organic LEDs offer greater flexibility and design possibilities, but can be more expensive to produce and less durable.

Hybrid perovskite LEDs could combine advantages of both technologies. Improving their efficiency and operational lifetime is an important step towards commercial applications.

The breakthrough began when researcher Sung-Doo Baek noticed that a batch of perovskite LEDs performed better than expected. The standard manufacturing process typically produced devices with an efficiency of around 20 to 25 percent, but the team’s results reached approximately 30 percent.

Baek investigated whether oxygen entering the nitrogen-filled laboratory enclosure might explain the difference. That hypothesis proved incorrect, prompting the researchers to examine the chemistry of the solution used to manufacture the LEDs.

The production process involves dissolving metal-halide salts and additives in a solvent. The solution is then applied in an ultrathin layer to a substrate before being heated to remove the solvent and form a crystalline perovskite structure.

After months of experiments, the researchers discovered that the duration of the heating process had a significant effect on the final device’s performance. Heating the solution for approximately 20 minutes produced the best results.

Further analysis revealed why. The heating process encouraged the formation of a linear chemical compound that improved the LED’s efficiency while suppressing the formation of a ring-shaped compound that reduced performance.

The team subsequently synthesised and purified the beneficial compound, then developed a method to control the chemical reactions involved. This approach increased the quantum efficiency of the perovskite LEDs to a peak of 37 percent.

Quantum efficiency measures how effectively a device converts electrical energy into light. The improvement therefore represents a substantial advance over the levels commonly achieved in earlier perovskite LED research.