Realization of Flexible Ultraviolet Organic Light‐Emitting Diodes: Key Design Issues

While organic light‐emitting diodes (OLEDs) have seen huge success as light sources in high‐end displays, efforts are being made to extend their spectral coverage beyond the visible region. Among such endeavors, the development of ultraviolet (UV) OLEDs is particularly of interest due to the unique applications of UV light in a variety of areas such as security, sterilization, phototherapy, etc. However, OLEDs that emit UV light are very challenging to realize due to limitations such as high‐energy‐induced molecular instability, the rarity of adequate emitting layers, and material optical properties that are very different from those of visible OLEDs. Herein, UV OLEDs are realized using 3‐(Biphenyl‐4‐yl)‐5‐(4‐tert‐butylphenyl)‐4‐phenyl‐4 H‐1,2,4‐triazole (TAZ) as emitters in both top‐emitting and bottom‐emitting configurations. High absorption of common plastic substrates is carefully considered, and semitransparent refractory characteristics of metals under UV are exploited to form flexible dielectric−metal−dielectric electrodes with high transparency in UV. As a result, highly flexible UV OLEDs with a peak wavelength of 371 nm and a full width half maximum as small as 13 nm are realized.