NPL and Samsung Institute offer insights into blue OLED performance

The precise causes of blue OLED degradation, whether physical, chemical, or otherwise, remain elusive, impacting the stability and thus the lifespan of OLED technology in colour displays and lighting applications.

The journey to enhance OLED technology began in 1975 at NPL with the invention of the first polymer light-emitting diode (PLED), which utilised a polymer film up to 2.2 micrometres thick sandwiched between two electrodes. Advances in red and green OLEDs have since brought their performance on par with traditional LEDs, but understanding and improving the durability of blue OLEDs has been a challenge due to the difficulty in chemically analysing the nanoscale organic layers that make up these devices.

Addressing this challenge, the NPL and SAIT team employed OrbiSIMS, a cutting-edge mass spectrometry imaging technique developed at NPL in 2017. This technique enabled them to detect degradation molecules in blue OLEDs with unparalleled sensitivity and pinpoint their location within the device's layers with a depth resolution of seven nanometres.

Their research identified that chemical degradation primarily occurs due to oxygen loss in molecules at the interface between the emission and electron transport layers. Additionally, OrbiSIMS revealed that using slightly altered host materials could significantly extend the OLEDs' operational life by an order of magnitude.

This study not only sheds light on the degradation pathways of blue OLEDs but also offers a methodology that could steer future enhancements in blue OLED designs, assisting manufacturers in creating displays with superior quality and longer lifetimes. The approach has already been applied in further research by Samsung and KAIST, also featured in Nature Communications.

Professor Ian Gilmore, NPL's corresponding author, emphasised: “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.”