Bright pure blue emission from multilayer organic electroluminescent device with purified unidentate organometallic complex

Multilayer organic electroluminescent devices (OELDs) were fabricated with highly pure 2-(2-hydroxyphenyl)benzoxazolato lithium (LiPBO), which was obtained through stepwise purification process, as a blue emission layer. The ionization potential of the carefully purified LiPBO was $\text{∼5.82\hspace{0.05em}}\mathrm{eV}.$ The multilayer OELD with a hole-blocking layer (HBL) emitted almost pure blue light with the CIE color coordinate of $\text{x=0.15}$ and $\text{y=0.08.}$ However, the emission color was redshifted when an electron-transporting layer (ETL) was introduced instead of the HBL. The device with both the HBL and the ETL showed stable and bright blue emission above $\text{14\hspace{0.05em}000\hspace{0.05em}}{\mathrm{cd/m}}^{\mathrm{2}}$ with the color coordinate of $\text{x=0.15}$ and $\text{y=0.11,}$ even though the color purity was slightly poorer than that with only the HBL.