Inquiries

High-refractive materials for low power display design L Corporation, Display Materials Research Department

High-refractive-index zirconia nanoparticle dispersion for energy-efficient applications

With unique design technology, it achieves both high refractive index and transparency.

Electronics
Surface Modification Environmental Friendliness

Resercher D (hereafter "D" )  from chemical manufacturer Company L is in charge of designing optical layers for display-related materials in the research department. The sales department received an inquiry from a client, a manufacturer of display panels for smartphones, regarding improving light extraction efficiency aimed at reducing power consumption, and D was scheduled to attend a meeting with the relevant parties.

* This is a hypothetical example posted as a reference for those with similar challenges

Challenges

Utilization of high refractive index materials to meet energy-saving requests for smartphones. The key is the optical layer design that balances display quality and power efficiency...

 D is in charge of designing the optical layers used in smartphone displays and participated in an internal meeting at the request of the sales department.

In response to the growing demand to reduce power consumption while maintaining display quality, discussions have been underway on how to enhance light utilization efficiency without significantly altering the driving conditions or light-emitting materials, while preserving compatibility with existing designs. One proposed direction is to improve light extraction efficiency by reviewing the optical layers.

After that, D attended a meeting with the sales representative and technical personnel from a smartphone display panel manufacturer. There, the participants expressed interest in approaches to reducing power consumption while maintaining display quality, and exchanged views on optical-layer-based solutions.

Through discussions, it was reaffirmed that while the approach of enhancing light extraction efficiency through the design of the refractive index of optical layers is effective, increasing the refractive index of materials can easily lead to light scattering and cloudiness, which poses challenges to display quality.

Upon returning to the research institute, D and the others advanced their specific considerations to achieve both a high refractive index and low scattering.

In this study, they focus on the approach of reducing optical loss by minimizing the difference in refractive indices between layers. By alleviating the refractive index gap, light is less likely to be trapped within the layers, and it is expected that the same brightness can be achieved with a lower driving current.

Additionally, they conducted studies on various nanoparticles with the aim of improving light extraction efficiency and alleviating the refractive index gap between layers.

Titanium oxide-based nanoparticles have attracted attention as inorganic materials with a higher refractive index than zirconia-based materials, and they have been studied for the purpose of designing the refractive index of optical layers. However, due to the inherent color and photocatalytic activity of the materials, there may be an impact on the stability of the optical layer through the degradation of organic components.

On one hand, zirconium oxide-based nanoparticles, although lacking in color and photocatalytic activity, have a refractive index that is inferior to that of titanium oxide-based nanoparticles. Furthermore, a general issue with inorganic nanoparticles is that depending on the particle size and dispersion state, light scattering can become apparent, which may lead to problems such as uneven display and increased haze in display applications.

Furthermore, organic materials excel in transparency and processability, and some can achieve relatively high refractive indices through molecular design. However, there are cases where the design options are limited when considering the design conditions to further increase the refractive index of the entire optical layer, as well as the need to simultaneously meet long-term reliability requirements, including durability and stability.

When the various materials were lined up like this, each had its own strengths and weaknesses, and D and the others found themselves deep in thought about which one would be the most realistic choice.

Key Challenges

  • There has been a growing demand for designs that maintain quality while reducing power consumption.

  • We examined multiple inorganic and organic materials as high refractive index materials, but it became clear that there are inherent constraints of the materials, such as the impact of light scattering on display quality and the upper limit of the refractive index for the optical layer as a whole.

  • Each material has its own strengths and weaknesses, making it difficult to select materials that simultaneously meet the requirements for light extraction efficiency, display quality, and ease of design.

Solutions

Solution Summary

  • ZIRCOSTAR™ (zirconium oxide-based nanoparticle dispersion) has a high particle refractive index of 1.86.

  • ZIRCOSTAR™ is designed to control particle size effectively, and with considerations for dispersion and agglomeration suppression, it is easier to reduce light scattering, contributing to the reduction of cloudiness and haze.

  • As a result, it is possible to enhance the design freedom of the refractive index while maintaining high transparency, which can be utilized in considerations for energy saving and the coexistence of display quality.

Zirconium oxide-based nanoparticles achieving a particle refractive index of 1.86. 'ZIRCOSTAR™' is a strong option!

D decided to participate in an electronics-related exhibition to explore new materials. There, they noticed a product called ZIRCOSTAR from Nippon Shokubai, which they had not known about before.

"I heard from the person in charge that zirconium oxide-based nanoparticles have a high refractive index, yet they become colorless and transparent when made into a film" (D said)

"I felt that it was a material that could be pinpointedly utilized for the current challenges, so I made an appointment for a meeting right there." (D said)

During a later meeting, he received an explanation that ZIRCOSTAR is a dispersion of zirconium oxide-based nanoparticles with a high refractive index of 1.86, and that it is designed with considerations for dispersion stability and transparency after the formation of optical layers, through surface treatment of the particles and the introduction of UV polymerizable functional groups.

Additionally, the design that alleviates the refractive index gap between layers has shown the potential to reduce losses caused by light confinement, which could lead to energy savings and heat suppression.

D found it particularly appealing that the inorganic materials was designed to maintain transparency not only in the dispersion state but also in the optical layer after UV curing, where cloudiness and aggregation are common concerns.

D is interested in the dispersion medium due to the abundance of information available about it, the presence of multiple lineups, and the higher solid content compared to other nano-dispersions, which makes it easier to adjust the particle content relative to the composition and facilitates the design considerations for refractive index adjustments.

"While achieving high brightness and energy efficiency, it seems promising to maintain transparency that leads to display quality and to have less unevenness. The fact that it can be implemented without significantly changing the existing structure also became one of the deciding factors, so we decided to evaluate ZIRCOSTAR" (D said)

Thus, D and others decided to proceed with the examination of ZIRCOSTAR as a candidate material for design conditions that require a high refractive index.

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