Single-emitter white OLED offers a simpler and more sustainable lighting technology

In an effort to create simpler next-generation lighting solutions, researchers at the University of Turku in Finland have developed a color-tunable white OLED. It is a top light emitting device that produces white light from a single organic layer and two standard aluminum electrodes, eliminating the need for rare indium tin oxide. This streamlined design is expected to replace the need for complex organic stacks with smart optics, reducing manufacturing costs and reliance on rare materials.

White OLEDs power high-end screens and are becoming more common in lamps and architectural lighting. However, traditional white OLEDs are complex. Manufacturers mix red, green, and blue dopants with heavy metals and add a transparent indium tin oxide (ITO) layer. By mixing these color-forming additives with the host organic layer in precise proportions, the device produces white light. However, these steps increase cost and waste and are not sustainable.

In a recent study published in Advanced Optical Materials, researchers at the University of Turku developed an innovative approach. They took a standard sky-blue metal-free TADF molecule (DMAC-DPS) and modified its light shape using tiny optical “holes in the mirror” known as microcavities.

This new device is top-emitting and does not use ITO. Both mirrors of the microcavity are made of common aluminum and serve as electrodes. The emissive layer is a single-component thin film based on the third-generation emitter DMAC-DPS, thus avoiding the cost and complexity associated with traditional host-guest chemistry and RGB color mixing.

Microcavities can be compared to small mirror holes because they reflect light in a similar way. In a new OLED technology developed by researchers, adjusting the cavity length (for example, by changing the thickness of the emissive layer) changes which colors are enhanced in the OLED.

At the same time, ripples of electromagnetic energy traveling along the metal surface, known as surface plasmon polaritons (SPPs), mix with the resonances of the cavity, broadening the spectrum from blue to white.

Combining these effects produces tunable white light from approximately 3,790 K (warm white) to approximately 5,050 K (cool white) without adding any additional materials.

“Our breakthrough is to get more for less,” says lead researcher Manish Kumar. “We have shown that complex RGB color mixing is not required to obtain beautiful white light. By letting carefully designed cavities and surface plasmons do the mixing, we turn a single blue emitter into a tunable white OLED using materials already familiar to manufacturers, no ITO, and a much simpler stack.”

The researchers’ invention has the potential to significantly reduce the ecological footprint and costs of OLED manufacturing, as it requires fewer rare input materials and processing steps. The design also fits neatly into existing vacuum deposition production lines. Because the device is “top-emitting,” it also works well on reflective and flexible surfaces, opening up options for sophisticated lighting fixtures, low-profile backlights, and future smart building panels.

“This study shows how clever optical design can replace chemical complexity,” says research group leader and professor Konstantinos Daskalakis. “By removing ITO and heavy metal dopants, we aim for lighting that is not only efficient, but also easier to manufacture, more sustainable, and environmentally and supply chain friendly.”

The researchers’ next steps are to investigate brightness, efficiency, and long-term stability in order to develop the lab prototype into a real-world lighting product.