Phosphorescent

Researchers from Seoul National University (SNU), in collaboration from colleagues from Samsung's SAIT institute, have identified a critical mechanism behind the performance degradation of OLED devices, the interfacial exciton-polaron quenching mechanism.

The researches have theoretically proposed a mechanism where excitons in the light-emitting layer are quenched by the accumulated charges at the interface. They followed with with experiments that have independently observed this phenomenon, identifying three key factors: interfacial barrier, exciton-polaron distance, and exciton lifetime. 

Researchers from Korea's UNIST institute, together with colleagues from Sungkyunkwan University have developed a new OLED intermediate layer material (with a highly unusual structure, twisted EBMs with anisotropic molecular arrangements) that significantly improves the brightness, efficiency and lifetime of blue phosphorescence OLED devices.

The researcher report that the new materials enable to reduce the operating voltage of the OLED display, thus enhancing the power efficiency by 24% and the operational stability by 21%. The researchers say that this new material can also be used for in-organic LEDs (including microLEDs).

Researchers from LORDIN, in collaboratioon with researchers from Korea's Dankook University, Gachon University and Hongik University, have reported on a highly efficient and stable ultra-pure blue phosphorescent OLED emitter, based on Lordin's Tetradentate Pt(II) material Complex with a vibration suppression effect.

The researchers say that the new emitter offers a lifetime of 451 hours (LT50 at 1,000 cd/m²), and an EQE of 25.1%. The emission spectrum is extremely narrow - full width at half a maximum of 22 nm. The researchers further developed a tandem OLED device based on this new emitter, which achieves an EQE of 50.3% and a lifetime of 589 hours (LT 70).

During iMID 2024, Samsung Display's eVP Yi Chung said that the company plans to reduce the power consumption of its OLED panels by over 50%. SDC is developing several technologies, each contributing to the same efficiency goal.

SDC did not detail its plans exactly, but it did mention some of the new technologies it is working on - polarizer-free OLEDs (these have been commercialized already), multi-frequency driving (demonstrated by other OLED makers), tandem OLED architecture and the adoption of high efficiency blue PHOLED emitters.

A report from Korea says that LG Display has successfully developed an OLED panel that is based on a blue phosphorescence emitter. The blue PHOLED, provided by Universal Display, offers 100% IQE, up from 25% used by current fluorescence emitters. This will result in around 20-30% power saving for the display itself (depending on the images shown).

UDC has been developing blue emitters for many years, and recently the company said that the development will take a few more months and won't be ready in 2024. The main challenge is increasing the lifetime of the materials. However LG Display has adopted a tandem design to enable a commercially ready display, perhaps even sooner than UDC planned.

Samsung Display's Lee Chang-hee, VP and head of SDC's research center, gave a talk during K-Display 2024, and updated that Samsung is progressing towards a next-generation blue OLED emitter technology in two tracks.

SDC is working with Universal Display, to adopt the company's blue PHOLED system. This is progressing, but SDC says that the pace is slow - indeed we heard from UDC lately that the introduction of a commercial material will take longer than expected.

OLED displays have been gaining popularity rapidly, and are already the dominant smartphone display technology. OLEDs are also the display technology of choice in the smartwatch market, making inroads into the TV, monitor, laptop and tablet markets. The future of the OLED industry looks bright.

In recent years, the focus of the industry, beyond increasing capacity and reducing production costs, has been improving the performance of OLEDs in the areas of display brightness, efficiency, and lifetime. Brightness is required in many applications - from TVs (for HDR and to view in ambient lighting) through smartphones (outdoor viewing) to automotive, and efficiency is a plus in any scenario (but mostly in mobile displays). Display lifetime is already good enough for many applications, but in some cases (like automotive, and IT displays) it is critical. These three properties usually go together - if you can make more efficient OLED displays, you can drive them at a lower current to achieve the same brightness, and so lifetime increases, or you can achieve higher brightness, etc. 

Researchers from Osaka University have found that thienyl diketone, a new organic molecule, shows high-efficiency phosphorescence, and one that is more than ten times faster than traditional organic phosphorescence materials. Such a material could hold promise for highly-efficient phosphorescence emission without the use of heavy metals. 

The researchers explain that phosphorescence occurs when a molecule transitions from a high-energy state to a low-energy state, and it often competes with non-radiative processes (i.e. heat generation instead of light). This competition with the non-radiative process leads to slow phosphorescence and lower efficiency. This is solved by adding heavy metal into the emitter - but this new breakthrough achieves fast emission without the heavy metal.