Correlation between ion impurity in thermally activated delayed fluorescence organic light‐emitting diode materials and device lifetime

Abstract

We propose a measurement method of ion impurity amounts of thermally activated delayed fluorescence (TADF) green dopant powders in a solution by applying a triangle voltage waveform and measuring a small displacement current that has been developed for screening and optimization of materials for thin‐film transistor‐liquid crystal displays (TFT‐LCDs). We found that there is a strong correlation between ion impurity and organic light‐emitting diode (OLED) lifetime, and we confirmed that the TADF green dopant, having a large number of ion impurity, has short OLED lifetime.

P‐134: Detection of Ion Impurities in Organic Thin Films by Displacement‐Current Measurement Method

“…The LC was non-polar liquid crystal, NA-1345 (DIC Corporation, Japan). The measurement conditions of DCM were set to 10 mHz of triangular wave voltage signal with ±10 V of applied voltage [10]. The I-V characteristics were measured three times at the temperature of 60 °C.…”

“…Inoue et al also have demonstrated to evaluate the behavior of lithium-fluoride (LiF) in OLEDs by DCM [9]. Recently, DCM was employed to detect the amount of ionic impurities in a solution of thermally activated delayed fluorescence (TADF) green emitting material, which was dissolved in xylene and filled into an LC cell [10]. It was realized that xylene contains many ionic impurities so it was difficult to accurately evaluate the amount of ions contained in the TADF emitter.…”