[Reading Science] OLED Screen Brightness Doubled with the Same Power

KAIST Researchers Develop "Quasi-Planar Light Extraction Structure"
That Reduces Crosstalk Between Pixels

A new technology has been developed that addresses the chronic issue of internal light loss in organic light-emitting diodes (OLEDs), long considered a fundamental limitation. This innovation enables screen brightness to be more than doubled with the same power consumption. There is growing attention on whether this breakthrough can simultaneously enhance both the brightness and efficiency, which are key performance factors for displays in devices such as smartphones and TVs.

On January 11, the research team led by Professor Yoo Seunghyup of the Department of Electrical Engineering at KAIST announced the development of a "quasi-planar light extraction structure" and a new OLED design method that can dramatically increase light efficiency while maintaining the planar structure of OLEDs.

Overview and Photo of the Quasi-Planar Light Extraction Structure. The research team first conducted a fundamental design to maximize radiative power transfer in finite-sized emission and reception areas, then applied a quasi-planar light extraction structure with precisely controlled curvature of the curved section and slope of the straight section. This minimized light loss caused by back-reflection within the structure and allowed more light to be emitted externally within a limited space. As a result, the proposed structure demonstrated higher brightness improvement compared to OLEDs without the structure as well as OLEDs equipped with micro-lens arrays (MLA) of the same size. Provided by the research team

OLEDs are widely used in smartphones and TVs due to their excellent color reproduction, thinness, and flexibility. However, because of their multilayer organic thin-film structure, more than 80% of the internally generated light is reflected or absorbed and lost as heat. As a result, the proportion of light emitted externally-known as external quantum efficiency (EQE)-has remained at around 20%.

Design Considering Pixel Size... Moving Beyond the 'Infinite Plane' Assumption

In the past, methods such as attaching hemispherical lenses or micro-lens arrays (MLA) to OLEDs have been proposed to extract more light. However, hemispherical lenses protrude and compromise the planar nature of the display, while MLAs must be much larger than the pixel size to achieve sufficient efficiency, leading to crosstalk issues between pixels.

The research team broke away from the conventional approach that assumed OLEDs as infinitely wide planes and instead presented an optical design method that considers the "finite pixel size" used in actual displays. The key was to optimize the structure so that light generated within each pixel is emitted directly forward, minimizing lateral leakage.

The newly developed quasi-planar light extraction structure is an ultra-thin design that maintains an almost flat OLED surface while efficiently extracting light to the outside. With a thickness of just about 50 micrometers, it achieves light extraction efficiency comparable to that of hemispherical lenses, which are over 2 millimeters thick. By maintaining a thickness similar to existing micro-lens arrays, it can also be applied directly to flexible OLEDs.

The team optimized the design through integrated optical simulations that encompass everything from the nanometer-scale OLED device structure to the millimeter-scale light extraction structure. As a result, OLEDs with the new structure achieved an external quantum efficiency (EQE) of 48.0% and a current efficiency of 192 cd/A, surpassing both conventional devices (EQE 35.6%) and devices with MLA applied (EQE 35.4%).

Photo of main authors. Top left: Kim Joungho, PhD at KAIST; bottom left: Kim Minjae, undergraduate at KAIST; Yoo Seunghyup, professor at KAIST. Provided by KAIST

Improvements Expected in Battery Life, Heat Generation, and Device Longevity

If this technology is applied, it will be possible to achieve brighter screens with the same power, leading to longer battery life, reduced heat generation, and extended display lifespan for mobile devices such as smartphones and tablet PCs. The research team explained that the technology can be applied not only to OLEDs but also to next-generation displays based on perovskite and quantum dot (QD) technologies.

This research originated from the KAIST Undergraduate Research Program (URP). Kim Minjae, the first author, said, "A small idea that came to me during class led to tangible research results." Professor Yoo Seunghyup emphasized, "We have presented a practical solution that maximizes efficiency while reducing crosstalk, even in displays composed of countless small pixels. The potential for expansion to next-generation displays, as well as OLEDs, is significant."

The research was jointly led by Kim Minjae, undergraduate student in Materials Science and Engineering (currently a doctoral student at Stanford University), and Kim Joungho, PhD in Electrical Engineering (currently a postdoctoral researcher at the University of Cologne, Germany). The results were published online in the international journal Nature Communications on December 29, 2025. The paper is titled "Near-planar light outcoupling structures with finite lateral dimensions for ultra-efficient and optical crosstalk-free OLED displays."

This research was supported by the KAIST Undergraduate Research Program (URP), the National Research Foundation of Korea’s Mid-Career Researcher Program, the Future Display Strategic Research Program, the Ministry of Trade, Industry and Energy’s Industrial Innovation Talent Growth Program, and the Electronic Components Industry Technology Development Program.