Solution based OLEDs

Researchers from Korea's Pusan National University have developed a new low-cost hole injection layer (HIL) material for solution-processed OLEDs, achieving higher efficiency and lifetime compared to the current state-of-the-art.

The new material is solvent-resistant (>99%) and thermally cross-linkable. The researchers used this material to create a solution-procssed red phosphorescent OLED device. The researchers placed the material between the ITO electrode and the HTL material, thus achieving photo-crosslinking of (poly-TPD) as HTL on top of crosslinked HIL. 

Researchers from Germany's Max Planck Institute, led by Prof. Paul W.M. Blom, are looking into single-layer OLED devices (in which a single emitting layer is sandwiched between two electrodes), with an aim to match their efficiencies to those of common multilayer OLED stacks, like the ones used in commercial OLED displays.

Current OLED architectures utilize multilayer stacks of materials, in order to increase the performance and lifetime of OLED devices. But according to the latest findings by Prof. Blom, equal efficiencies can indeed be met with single-layer TADF OLED emitters - and there's no fundamental reason or major benefits that arise from multilayer OLEDs.

Samsung Display has developed a 18.2" 2560x1440 202 PPI inkjet-printed OLED display, that features the highest current efficiency of any inkjet-printed OLED, with the brightness at 350 cd/m² (full white).

Samsung Display says that the high brightness was achieved by tuning the top-emission device structure with high performance soluble materials. The high pixel resolution was achieved by modulating the jetting waveform for ejecting ink drops and improving the drop placement accuracy by selecting the right ink formulations in terms of viscosities and surface energies.

Digitimes reports that AU Optronics has setup a 3.5-Gen test ink-jet OLED printing line, and the company now intends to start building a 6-Gen production line. AUO will start constructing the line before the end of 2019.

AUO's Chairman confirmed that the latest advances in printing materials and equipment are starting to make OLED printing viable for commercial use. AUO has not yet decided the schedule for volume production.

LG Chem has acquired DuPont's soluble OLED technologies and assets, in a deal estimated at $175 million. LG Chem will receive DuPont's entire soluble OLED IP (540 materials and process patents) and all of DuPont's related equipment and R&D facilities. The deal does not include any assets related to Dupont's evaporation OLED business.

LG Chem believes that the OLED industry is moving towards ink-jet printing of OLED panels based on soluble OLED materials and technologies - and it has now acquired key technologies in this area. DuPont has been developing related materials for over 20 years, has been collaborating with equipment makers (such as Kateeva) and display makers and has also developed its own nozzle-printing process.

At the OLED Korea conference, both Merck and Sumitomo detailed their latest OLED inkjet material performance.

Sumitomo is advancing with its R&D efforts, and the company says that its PLED materials will be adopted in mass production systems by 2020 (although JOLED already uses PLEDs in its displays).

UBI Research estimates that AMOLED shipments reached 440 million units in 2017 (up 13.6% from 2016), with revenues reaching $27.1 billion (up 62.3% from 2016). Only yesterday did DSCC release its own estimates of $23.2 billion in revenues for the AMOLED market in 2017.

The AMOLED market is expected to grow at a CAGR of 17.5% to reach almost a billion units in 2022. Revenues will grow faster at 22% and reach $80.5 billion in 2022.

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 SOLEDLIGHT (Solution Processed OLEDs for Lighting) project was launched in 2015 by a European consortium with an aim to develop cost efficient, roll-to roll (R2R) solution processed OLEDs, including their integration in prototype multiple-panel OLED lighting systems and luminaires.

The SOLEDLIGHT consortium (which is coordinated by the University of Valencia and includes OSRAM and Solvay) reported that it managed to develop multi-layer R2R solution processed OLEDs that achieved a power efficiency of 20 lm/W. This is still not up to par with evaporation-based OLEDs, but the project partners aim to achieve 100 lm/W (and 15,000 hours) by the end of 2017.