Study of Impurity Diffusion through an OLED Device Interface by Backside SIMS

Abstract

Although changes in the layer structure of an OLED as well as the diffusion phenomena in cathode materials and in EIM (electron-injection material) have been discussed actively, fundamental questions have remained unanswered. Using backside SIMS technique after optimised preprocessing of OLED samples, it has been possible to measure more accurate profiles of diffused elements, which was quite difficult under conventional SIMS analysis from the front surface due to so called knock-on effect. We have utilized the backside SIMS in the deterioration evaluation of OLED devices under the high temperature storage condition. Diffusion of EIM has been found with the change in layer structure depending on Tg (glass transition temperature) of HTM (hole transport material). On the basis of the analysis, it was found that the diffusion of EIM and the change in the layer structure depended on the Tg (glass transition temperature) of the HTM (hole-transport material) at the deterioration evaluation during high-temperature storage.

Molecular depth profiling of multilayer structures of organic semiconductor materials by secondary ion mass spectrometry with large argon cluster ion beams

“…For the sample annealed at 120°C, the intensities of Alq ions at the original NPD layer increased slightly and the diffusion of Alq 3 molecules was confirmed directly by the analysis of the molecular ion signals. The diffusion of Alq 3 molecules into the hole‐transport layer stored at 120°C for 30 min was also obtained indirectly from the profiles of Al + signals by using backside SIMS analysis 27. In contrast, diffusion of NPD molecules was not observed for the sample annealed at 120°C.…”