CES 2021: All-Digital but Virtually IRL with OLED Technology
As we turn the corner into 2021, we head straight into CES, the premier annual showcase of consumer electronics innovation. This year’s event will feature 1000 exhibits and 100 programming hours. It’s all digital but virtually In Real Life (IRL), thanks to continuous innovations in display technologies.
For the legions of visitors tuning in through their high-end devices, the viewer experience is more immersive than ever. Because in spite of the pandemic, leading brands continued their tradition of rolling exciting new smartphones. Apple introduced its family of iPhone12s, Samsung released its latest foldable device, the Galaxy Z Fold 2, and Huawei debuted its P40 Pro – all featuring OLED technology.
The advantages of OLED technology are well known. Unprecedented color clarity, as well as flexible displays that catalyzed devices like the Galaxy Z Fold, and much more. Such advantages are fueling fast growth for the OLED display market worldwide. In China alone, companies collectively invested $49B in OLED technology in recent years to build 12 OLED production lines. Seven more are under construction.
Yet there are still untapped efficiencies that could further maximize the performance of the OLED device. With new emitter materials innovations, next-generation smartphones will come with greater power efficiency and even longer battery lifetime.
In our first blog of 2021, we invited one of our scientists to “open the hood” of the OLED emissions layer and explain how materials innovation will improve the power-efficiency of next-generation smartphones.
Blue: It’s what gives OLEDs Power
The Process that Leads to Light Emission
In the OLED stack, there are two types of charges: electrons (with a negative charge) and holes (with a positive charge). When a voltage is applied, the charges travel across opposite sides of the device towards the emissive layer. Here, the opposite charges meet and form a so-called exciton. After a short amount of time the exciton decays and emits light. The ratio between the number of photons emitted from the surface of the device and the number of injected charges is a measure for efficiency. It’s called external quantum efficiency (EQE). Other essential parameters like color, power efficiency and lifetime are heavily influenced by the processes in this layer.
The emitter materials found in today’s OLED products (TVs, smartphones, etc.) are the result of 30+ years of R&D led by industrial/academic collaborations.
The Intersection of Red Green & Blue
An OLED display consist of three different kinds of pixels – Red, Green and Blue. By combining these colors, the whole color gamut can be displayed. Each pixel is a separate OLED device and for each color the emitter differs substantially. Red and Green are phosphorescent emitters that use heavy-metal, rare-earth materials to achieve high efficiency and lifetime of the display
Blue: The Source of New Efficiencies
Blue is the outlier. Since Blue phosphorescent emitters show a very poor lifetime, they cannot be used in an OLED display. Blue light has a much higher energy than red and green light. In fact, the energy is so high that the materials in phosphorescent blue OLEDs degrade much faster than in Red and Green phosphorescent OLEDs. To solve this problem, Fluorescent materials are used as the emitters. While they are much more stable than Blue phosphorescent emitters, efficiency is poor.
Blue is the least efficient emitter. While Red and Green phosphors can use 100% of the excitons to emit light, fluorescent materials are limited to only 25%. Within a device, this translates into maximum EQEs of 25-35% of Green and Red but only 10% for Blue pixels. The discrepancy affects power consumption. In mobile phones, Blue consumes up to 10% of total power consumption. Improving efficiency is the fundamental pathway to reduce power consumption and enable longer battery lifetime.
CYNORA’s Fluorescent Blue Approach
CYNORA addresses the efficiency imperative with its Fluorescent Blue product, the cyBlueBooster.TM The approach uses a host material that carries the charges to the emitter (as typical OLED hosts do), while also functioning as a pump for efficiency by transferring its energy into the emitting Blue material. This approach increases the exciton utilization efficiency from 25% to around 40%, and improves the EQE to >10% without affecting device stability. By leveraging CYNORA’s extensive experience in molecular design, the intrinsic efficiency of the material is further improved. The overall effect is an increase in the lifetime of the Blue pixel, and a performance boost for the Blue emitter.
Efficiency is only part of the story. Color purity and material stability can also challenge the fluorescent Blue approach. Color purity is a combination of peak emission and peak sharpness. True deep Blue color purity can only be achieved with precise emitter material design strategies. If a material is off-spec, significant changes in the OLED stack must be implemented to optimize the pixel performance. This is costly and burdensome in large production facilities. Lifetime is the final piece since not all Fluorescent Blue dopants can achieve the stability required to make them successful candidates for displays.
While recent materials innovations have yielded material dopants that deliver high efficiency OR good color purity with ranging lifetime values, CYNORA’s fluorescent Blue offers both in a single emitting material. When compared to similar products, it delivers efficiency gains of >15% and true color purity (<30nm full-width at half maximum) with lifetime advantages that make it a good fit for today’s applications. Available in different shades of Blue, it lets display makers select and optimize the emitter for their unique products, without changing their OLED stacks or processes.
A better Blue means that the next generation of smartphones can achieve a lower power consumption of the Blue pixels (and therefore the displays), while further improving the color quality – without sacrificing lifetime.
(Image credit: CES)