Air Stable Organic Salt As an n-Type Dopant for Efficient and Stable Organic Light-Emitting Diodes

Air-stable and low-temperature-evaporable n-type dopants are highly desired for efficient and stable organic light-emitting diodes (OLEDs). In this work, 2-(2-Methoxyphenyl)-1,3-dimethyl-1H-benzoimidazol-3-ium iodide (o-MeO-DMBI-I), a thermally decomposable precursor of organic radical o-MeO-DMBI, has been employed as a novel n-type dopant in OLEDs, because of its air stability, low decomposition temperature, and lack of atom diffusion. The n-type electrical doping is evidenced by the rapid increase in current density of electron-only devices and the large improvement in conductivity, originated from increased electron concentration in electron-transport layer (ETL) and reduced electron injection barrier. A highly efficient and stable OLED is created using o-MeO-DMBI as an n-type dopant in Bphen. Compared with the control device with its high-temperature-evaporable n-type dopant cesium carbonate (Cs2CO3), o-MeO-DMBI-doped device showed an incredible boom in current efficiency from 28.6 to 42.2 cd/A. Moreover, the lifetime (T(70%)) of o-MeO-DMBI-doped device is 45 h, more than 20 times longer than that of the Cs2CO3-doped device (2 h). The enhanced efficiency and stability are attributed to the improved balance of holes and electrons in the emissive layer, and the eliminated atom diffusion of cesium.