Study on Intrinsic and Extrinsic OLED Degradation by Utilizing μ-PL with Gradient Shaping Preparation and GCIB-XPS/REELS

We demonstrated analysis of phosphorescent organic light-emitting diode (OLED) degradation by utilizing micro-photoluminescence spectroscopy (μ-PL) combined with gradient shaping preparation. We also investigated the degradation mechanism by utilizing X-ray photoemission spectroscopy (XPS) and reflected electron energy loss spectroscopy (REELS) combined with gas cluster ion beam (GCIB) depth profiling. These methodologies provide us with valuable insights such as intrinsic degradation of the electron blocking interface through device operation and extrinsic degradation due to contamination of an acceptor material by a brominated compound.

The dominant cause of the intrinsic degradation in our co-host system was due to deterioration of the donor host material, leading to a charge imbalance and subsequent formation of immobile exciton quenchers at the electron blocking interface. Besides, in the case of extrinsic degradation, we found from GCIB-XPS/REELS a presence of built-in potential in the device due to spontaneous orientation polarization (SOP). The Br contaminant of the acceptor host material induced polarization across the hole blocking layer, which expedited the deterioration of the electron blocking interface due to an uneven electrical field in the emission layer. 

It is noteworthy that analysis and manipulation of SOP have been hot topics in recent years for, e.g., efficient organic photovoltaics. The combination of gradient shaping μ-PL and GCIB depth profiling is useful not only for degradation analysis but also designing of efficient organic electronics devices.