OLED (Organic Light Emitting Diodes) is a flat light emitting technology, made by placing a series of organic thin films (usually carbon based) between two conductors - and these films light up when electrical current is applied. OLEDs are used to make display and lighting panels. OLED displays are thinner, more efficient than LCD displays, and they offer a far better image quality.
One of the most exciting features of OLED displays is that they can be made flexible. Can you image foldable phones that open to become tablets, TVs that can be rolled up when not in use and lighting panels that wrap around round pillars? Flexible OLEDs can enable all of that, and more.
One of the major problems with those organic materials is that they are very sensitive to oxygen and moisture. This means that OLEDs need to be protected - as even a single water or oxygen molecule can harm the OLEDs.
Thin Film Encapsulation (TFE)
With regular (rigid) OLED panels, the solution is simple - you can use a strong glass sheet. Glass is a great barrier, and it is widely used in the display industry and so easy to
For flexible panel, rigid glass is obviously not an option, and in such panels producers use different techniques, collectively referred to as Thin Film Encapsulation, or TFE. TFE is a multi-layer film, made from alternating organic and inorganic layers.
Most organic layer TFEs use an inkjet printing process. Inkjet printing is usually associated with micro-scale OLED deposition, but the technology can also be used to deposit organic TFE materials. Kateeva (an OLED inkjet printing pioneer) has launched an encapsulation inkjet printer system towards the end of 2014, and in 2016 the company announced that it secured the "vast majority" of available TFE orders, and its customers include the world's largest flat-panel display makers in three key Asia regions.
Kateeva says that inkjet printing can achieve exceptional large-area uniformity, and it is the only technology with sufficient accuracy that offers the capability to coat and pattern the edges in a single step. Kateeva produces and markets its own encapsulation materials, but the systems can also use materials from other makers.
The inorganic TFE material deposition can be done in different methods, and several companies are targeting this market. The incumbent technology for the inorganic TFE deposition is Plasma-enhanced chemical vapor deposition (PECVD) which seems to be currently used by both Samsung and LG Display.
Atomic Layer Deposition (ALD), which is a modification of the basic CVD process, can also be used to deposit these materials, and it seems that this newer technology is gaining ground in the TFE market as it enables thinner and more uniform films. Several companies develop ALD-based OLED encapsulation systems, and as early as 2012 Beneq shipped a large-area flexible OLED ALD system to a "leading Asian customer". In 2017 Encapsulix also announced it supplied mass production ALD-TFE equipment to a leading Asian AMOLED producer.
The latest OLED encapsulation news:
Samsung Display is developing hybrid QD-OLED TV technology, and according to estimates, the company aims to begin trial production in 2019. It is also estimated that Samsung has several challenges to overcome, but according to new reports from Digitimes, Samsung is aiming to start installing equipment for the new fab as early as December 2018.
The new fab will begin operation in the second half of 2019 - pilot production at first which will be expanded to full scale mass production. The new fab will be built in Samsung's L8 LCD production line in Asan, and will take over one of the two lines currently in operation at the fab. Samsung's initial production capacity will be around 25,000 monthly G8 substrates.
The EU-funded Flexolighting project believes that OLED lighting cost can be reduced to 1 Euro per 100 lumens
In 2015, the EU launched the €4.4 million Flexolighting project (led by Brunel University London) with an aim to develop new materials, processes and methods to overcome current OLED lighting challenges - including lifetime, lighting uniformity and more.
The project's consortium announced that following the project completion and a rethinking of the complete OLED supply chain, it believes that high efficiency OLED lighting panels can be produced at a cost that is on a similar level with LED lighting.
Japan-based Meidensha Corporation announced that it has developed a new technology to deposit barrier films for bendable displays and electronics. The new process is done at very low temperatures (30 C) which can significantly lower energy costs compared to current plamsa-based processes (usually run at 100-150 C).
The new technology uses a 100% ozone environment. Together with Japan's AIST, Meidensha developed a device that continuously generates pure ozone. This technology was patented earlier this year.
OTI Lumioncs launches its new Aerelight for print technology, aiming to embed flexible OLED lighting in print media
OTI Lumionics launched a new technology it calls Aerelight for Print technology, which uses paper-thin flexible OLED panels to light elements in print media.
OTI says that in order to enable low-cost production of flexible OLEDs, it designed its own manufacturing technology and advanced materials. This includes the company's own proprietary FlexTorr encapsulation technology.
BASF's Coatings division announced that OLEDWorks uses the company's flexible barrier solutions in its Bright 3 family of OLED panels (both flexible and rigid). OLEDWorks uses BASF materials as planarization layer to enable highly reliable thin-film encapsulation.
Taiwan's AU Optronics (AUO) developed a 13-inch 100 PPI transparent OLED display, specifically for AR applications. This is a highly-transparent display - with 68% transmittance.
AUO 6" transparent OLED prototype (2011)
To achieve such high transparency, AUO optimized the TFT array layer stack, the OLED cathode pattern and the encapsulation. This is the first transparent OLED AUO has developed since 2011. It will discuss this new display at SID Display 2018 - and will hopefully demonstrate it as well.
Many OLED producers believe that Ink-Jet printing of OLED emissive materials is the best way to achieve lower-cost OLED TV production, and to enable OLEDs to compete in the medium part of the TV market. Ink-Jet printing is an efficient process (less material waste compared to evaporation) and it can be very quick as well. The main drawbacks of inkjet are the limited resolution and the need for soluble emissive materials which are less efficient compared to evaporation ones.
A Kateeva OLED ink-jet printing system
These challenges are being overcome, and it seems that at least four groups (in Korea, Japan and China) are charging forward towards mass production of ink-jet printed OLEDs. Ink-jet printer makers and soluble material suppliers are also optimistic ink-jet printing commercialization will soon be here as the material performance gap is diminishing.
In 2015 the EU launched a 3-year €4 million OLED lighting project, the LEO project (Low-cost / energy Efficient OLEDs) that had an aim to develop efficient and cost-effective bendable OLED lighting technologies. The project consortium included Osram, and Cynora.
A month before the project officially ends, the partners updated on their progress. For this project, the partners develops several technologies, including low-cost metal foils integrating OLED anodes and possibly backside monitoring printed circuits, smart OLED top-electrode architectures and light out-coupling solutions and a novel thin film top-encapsulation strategies. These technologies together increased the light output by 50% while providing better surface scratch resistance.
The Holst Centre is demonstrating a new optimized encapsulation (barrier) layer for foldable OLED panels. The new barrier is made from an organic layer sandwiched between two layers of silicon nitride (SiN). These are standard materials, but by optimizing the stack design the researchers at the Holst Centre were able to control its mechanical properties and create a much more flexible barrier.
The Holst researchers used an organic material that can withstand 400 °C and can be applied by slot-die coating. This allows the SiN layers to be deposited at 350 °C, improving their quality and ability to prevent water penetration. The Holst tested the OLED prototypes that use the new barrier for 1,000 hours (in accelerated lifetime testing) and no black spots appeared, even after 10,000 folding cycles (bending radiud 0.5 mm).
Graphene is the world's most impermeable material, and as the material is also transparent, flexible and ultra-thin it makes sense to adopt graphene as an encapsulation layer for next-gen OLED displays. A UK project led by Cambridge University researchers have set out in 2015 to develop such a solution, and the researchers now report that they have demonstrated a viable graphene solution comparable to existing commercial OLED encapsulation technologies.
In its pure form, graphene is permeable to all gases, but real life materials are never entirely pure and defects and holes harm the material's permeability. The new research used ALD and CVD to create large-area high-quality single-layer graphene sheets which were stacked to create a multi-layer coating. The researchers say that a ~10 nm barrier layer that includes 3-4 layers of graphene (with AlOx in between) is an effective solution for OLED displays. The 10 nm layer maintains a high optical transparency (>90 %) and high flexibility.