10x breakthrough for blue OLED performance
A groundbreaking study by the UK’s National Physical Laboratory (NPL) and Samsung is providing new insights on improving blue organic light-emitting diode (OLED) performance for displays and lighting.
The researchers at NPL and the Samsung Advanced Institute of Technology (SAIT) have been studying the degradation mechanisms of blue OLED displays to boost the performance of full colour displays and lighting by a factor of 10.
The first polymer light-emitting diode (PLED) was created at NPL in 1975. It used a polymer film of up to 2.2 micrometers thick located between two charge-injecting electrodes. Since then, developments in red and green OLED technology related in these coloured OLEDs being now comparable to conventional LEDs.
Understanding the degradation mechanism of blue OLEDs is essential to improve their performance and stability. However, OLEDs are formed of very thin layers of organic molecules, and chemically sampling nanoscale organic layers and interfaces with enough analytical information is challenging.
To tackle this longstanding problem, the NPL / SAIT team used OrbiSIMS, a mass spectrometry imaging technique invented at NPL in 2017. The team used OrbiSIMS’ nanoscale mass spectrometry to identify, for the first time, degradation molecules of blue OLEDs with unprecedented sensitivity and localise them with seven nanometres depth resolution within the OLEDs multi-layered architecture.
The team found that chemical degradation is mainly related to loss of oxygen in molecules at the interface between emission and electron transport layers. The OrbiSIMS results also showed approximately one order of magnitude increase in the lifetime of OLED devices that use slightly different host materials.
The method has already been used in another study led by Samsung and the Korea Advanced Institute of Science & Technology (KAIST), which also published in Nature Communications.
“Our research enabled us to identify degradation molecules that are reaction products localised at the interface between emission and electron transport layers (ETL/EML). The presence of these degradation molecules correlates negatively with the blue OLEDs lifetime. Furthermore, we showed that devices with subtly modified host materials have much reduced intensities of the interfacial degradation products and exhibit superior lifetime,” said Dr Gustavo Trindade, one of NPL lead authors of the study in Nature,
Professor Ian Gilmore, NPL corresponding author of the study, said, “OrbiSIMS allows high confidence in the identification of complex molecules with attomole sensitivity and simultaneous localisation to a layer of less than seven nanometres. This cannot be achieved using traditional High-performance LC-MS methods requiring dissolution of the device. OrbiSIMS as a diagnostic tool for degradation of OLEDs can play a vital role in providing insight for future material and device architecture development.”
The research is already being applied to Samsung display development.
“We were delighted to work with Professor Ian Gilmore’s NPL team to apply the OrbiSIMS for the first time to study the degradation of blue OLEDs, which is currently one of major obstacles for the industry. Thanks to the development of the OrbiSIMS with its unprecedented depth/mass resolution and the ability of the intact analysis of organic molecules, we can now diagnose and answer a variety of outstanding problems in organic electronic devices such as OLEDs,” said Dr Soohwan Sul and Dr Joonghyuk Kim, SAIT lead authors of the study.
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