"Breaking the limits of OLED: Postech achieves low-votage freely color tunable ultra-pure laser emission"

A new class of laser emission technology enabling ultra-high color purity and continuous spectral tunability at low voltage has been developed, marking a significant advance beyond conventional display light sources.

 

A research team led by Prof. Su Seok Choi of the Department of Electrical Engineering at POSTECH (Pohang University of Science and Technology)—including Hyerin Kim (M.S.), Jeongwoo Park (integrated M.S.-Ph.D. program), and Wontae Jung (Ph.D. candidate) among others—has demonstrated a next-generation laser emission platform capable of precise color control under battery-level low voltage. The study was selected as an Inside Front Cover article in the international optics journal Laser & Photonics Reviews, underscoring its scientific significance.

 

The clarity and purity of color are fundamentally determined by how narrowly light is confined within a specific wavelength range, typically quantified by the full width at half maximum (FWHM) of the emission spectrum. Conventional OLED-based displays exhibit relatively broad emission spectra (FWHM ~40 nm), while even advanced quantum dot (QD) emitters remain around ~30 nm. These intrinsic spectral limitations restrict color purity and pose critical challenges for emerging applications such as holographic and advanced AR/VR displays, which require laser-like ultra-narrowband (~1 nm) emission for precise optical wavefront and phase control.

 

In addition, existing display technologies rely on the color mixing of discrete red–green–blue (RGB) emitters, leading to structural complexity and limited capability for continuous spectral tuning. Achieving both ultra-high color purity and continuous wavelength tunability within a single device has remained a long-standing challenge.

 

To address these limitations, the research team introduced a novel photonic architecture that integrates OLED emissive materials with chiral liquid crystals (CLCs). The helically ordered structure of CLCs forms a periodic resonant cavity capable of selectively amplifying specific wavelengths. By coupling broadband OLED emission into this chiral resonant structure, the team successfully transformed it into laser-like emission with an ultra-narrow linewidth of approximately 1 nm (FWHM), achieving color purity tens of times higher than that of conventional OLEDs.

 

Beyond spectral narrowing, the team also achieved continuous wavelength tunability within a single device. By employing an electrothermal actuation mechanism, small electrical inputs induce controlled thermal modulation of the CLC helical pitch, thereby shifting the resonance wavelength. Notably, this enables continuous color tuning over a wide visible spectral range of approximately 135 nm under a low driving voltage below 1.5 V, overcoming the high-voltage limitations of conventional tunable laser systems.

 

Importantly, the proposed platform achieves this functionality within a single-pixel architecture. Unlike conventional displays that require multiple RGB subpixels, the device can generate a continuous spectrum of colors from a single emissive unit, significantly simplifying the device structure and enabling high integration density for future display and photonic systems.

 

This work is particularly notable in that it realizes ultra-high-brightness emission together with low-voltage, color-tunable vertical-cavity lasing—key attributes for next-generation display applications.

 

This work represents a comprehensive breakthrough that simultaneously overcomes three key limitations of conventional light sources: high driving voltage, broad emission spectra, and complex multi-emitter architectures. By integrating low-voltage operation, ultra-high color purity, and continuous spectral tunability into a unified platform, the technology opens new possibilities for next-generation photonic applications.

 

Potential applications include holographic displays, AR/VR and micro-displays, ultra-high color gamut imaging systems, wavelength-tunable optical communications, biosensing, optical encryption, and next-generation photonic semiconductor devices for AI.

 

Professor Choi commented, “By combining OLED materials with chiral liquid crystals, we have demonstrated laser-grade ultra-high color purity emission and precise wavelength control at practical low voltages. This work establishes a new platform that could fundamentally transform the architecture of displays and optoelectronic devices.”

 

This research was supported by the Samsung Future Technology Foundation under its designated display research program.

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