Organic light-emitting diodes (OLEDs) have been attracting much attention due to their compatibility with flexible and surface-emitting form factors. However, OLED research has been limited mainly to the visible spectral region, and OLED studies emitting ultraviolet (UV) spectra have seldom been reported. This is partly because it is challenging to realize UV OLEDs due to the absence of an efficient and stable organic light-emitter in UV. Furthermore, there are many additional aspects to consider in the case of UV OLEDs. For instance, certain types of electrodes or plastic substrates absorb a rather significant amount of UV rays, making it even more difficult to realize flexible UV OLEDs.
In this study, the 3-(Biphenyl-4-yl)-5-(4-tert-butylphenyl)-4-phenyl-4H-1,2,4-triazole (TAZ), typically used as an electron transport layer (ETL), was used as a wide gap fluorescent emitter emitting UV light in the UVA spectrum. The substrate absorption issue was circumvented by introducing a top emission structure. Furthermore, the microcavity effect was used to tune the peak wavelength and decrease the full width at half maximum (FWHM). OLEDs emitting around 375 nm with FWHM as small as 13 nm.