Sensitive non-destructive real-time monitoring of blue OLED materials on extreme surface using terahertz near-field enhancement

Chemical degradation phenomenon of organic materials is fatal to commercial applications requiring high-efficiency and long-lifetime organic light-emitting diodes (OLEDs), but its mechanism is not fully understood yet. It is preferable to exclude all stimuli that may directly or indirectly affect the degradation process of the chemically unstable organic materials when investigating the materials. In this report, we introduce terahertz (THz) spectroscopy by taking advantage of low photon energy and deep penetration depth. We monitored the photo-degradation in DPEPO, mCBP, and mCP for blue light emission induced by photodissociation of the molecules. Measured THz transmittances present the aging process of the organic materials in a non-destructive manner. A nano-metamaterial-based sensing chip which induces strong field enhancement at the local surface was introduced for highly sensitive detection of chemical conformational change on extreme surfaces of tens of nanometer thickness. Our advanced non-destructive and real-time monitoring system is expected to contribute to the field of such organic materials for its fundamental scientific aspect as well as for its potential impact.