Diffuse light sources such as organic LEDs, or OLEDs, offer a flexible, glare-free option for luminaire design. However, current OLED lighting is limited by low light-extraction efficiency, even though they have very high internal light-production efficiency. Pixelligent Technology is teaming with OLEDWorks to develop and demonstrate advanced OLED materials and methods.
Pixelligent research funded through the DOE Small Business Innovation Research (SBIR) program has advanced the materials science used to create internal light extraction layers for use in OLED panels, through the use of high-refractive-index (HRI) layers that are embedded with light-scattering particles. In 2017, the team developed a novel internal light extraction (ILE) design to improve the light extraction efficiency of OLED lighting devices to 70% without negatively impacting the device voltage, efficiency, or angular color dependence. The innovative structure is positioned between the OLED device stack and the glass or polymer substrate, enhancing light outcoupling by reducing waveguiding losses in the OLED stack. These losses occur due to reflections resulting from an index of refraction mismatch at the device/substrate interface. Pixelligent’s ILE combines scattering particles in a HRI matrix. The HRI matrix has an index of refraction between that of the device stack and the substrate, resulting in fewer interfacial reflections and waveguiding losses. The larger (hundreds of microns) TiO2 scattering particles embedded in this matrix serve to scatter light out of the device. This HRI-ILE technology is enabled by Pixelligent’s proprietary, high refractive index, highly transparent ZrO2 nanocrystals. Extensive research has been conducted to optimize the index of refraction of the ILE materials, determine the appropriate scattering size and loading densities, and formulate the materials for proper particle distribution and processibility.
In subsequent projects, the team utilized the extremely small size of the HRI nanoparticles to create gradient index films with a simple coating process. They have continued to optimize the process for gradient film manufacturing and the scattering layer configuration and processing. In 2018, Pixelligent commercialized their ILE formulations, which are fully compatible with multiple OLED device manufacturing processes and operating conditions, helping to expedite the commercialization of OLED lighting. HRI-ILE OLEDs are cost effective due to the use of highly scalable materials and the low-cost manufacturability of Pixelligent materials.
Pixelligent teams with OLEDWorks to demonstrate their cost-effective, high-refractive-index nanocomposite formulation in a well-characterized OLED device manufactured by OLEDWorks. In 2021, Pixelligent’s HRI-ILE integrated OLEDs demonstrated an efficacy as high as 117 lm/W at 3,000 cd/m2 with a Duv <0.008 and CRI of ~84 in prototype devices. In comparison, the efficacy of the state-of-the-art OLEDWorks Brite 3 panel (currently available in the market) is 85 lm/W. With the OLED lighting market moving toward niche applications, such as bendable light panels, Pixelligent’s ILE has also successfully been tested in flexible prototype devices. (August 2021)
Return to Research Highlights.
