Magneto-electroluminescence in organic light-emitting devices and its role in study of device physics

In the past decade magnetic field effects (MFEs) of organic semiconductors have been extensively studied. Due to the ambiguity of the underlying mechanism, the research of organic MFEs has experienced an intense debate. To clarify the underlying mechanism, we firstly investigated the MFEs of organic light-emitting devices (OLEDs) under balanced ambipolar injection through the method of transient electroluminescence (EL). The results indicate that the electron-hole pair model and triplet-triplet annihilation model are suitable to explain the magneto-electroluminescence (MEL) in OLEDs under balanced ambipolar injection. We then explored the inter-conversion between singlets and triplets in charge-transfer (CT) fluorescent OLED via the MEL measurements. The results give an experimental evidence of the occurrence of revised intersystem crossing in CT materials, and show that the inter-conversion between singlet and triplet is a dynamic-balance process. Our work demonstrates that MFEs can be used as a powerful tool to study the physical processes in organic semiconductors.