Narrow‐Band Deep Blue Emission in Organic Light‐Emitting Diode at 1.5 V

Blue organic light‐emitting diodes (OLEDs) are essential components in optoelectronic devices, providing high‐energy emissions for vibrant displays and white light illumination. However, their widespread application is hindered by high operating voltages and limited operational lifetimes. Upconversion (UC)‐OLEDs, which utilize the triplet–triplet annihilation (TTA) UC process to emit light, offer blue light emission with an ultra‐low turn‐on voltage of 1.5 V, thereby reducing energy loss and enhancing device longevity. Despite these advantages, the strategy for selecting dopant—key determinants of emission color in UC‐OLED—remains unclear, leading to the emission of impure sky‐blue light in a previous report. This study investigates the effect of dopants on UC‐OLED performance by examining how molecular structure and properties affect charge transport through the formation of deep traps, thereby elucidating dopant selection rules. By developing optimized dopants, a UC‐OLED capable of emitting narrowband deep‐blue light at 447 nm with a full width at half maximum (FWHM) of 20 nm, driven by a 1.5 V battery, is demonstrated.