Stable pure-blue hyperfluorescence oleds

Organic light-emitting diodes (OLEDs) are a promising lightemitting technology useful for various display applications^1,2. Despite great progress in this field^3-12, there is an ongoing challenge to realize high performance blue OLEDs with efficiency, good color purity, and device lifetime. Here, we report pure-blue (CIEx,y color coordinates of [0.13, 0.16]) OLEDs with high-efficiency (external quantum efficiency of 32 % at 1000 cd m^–2), narrow-emission (full-width half maximum of 19 nm), and good stability (LT95 of 18 hours at an initial luminance of 1000 cd m^–2). The design is based on a two-unit stacked tandem hyperfluorescence (HF)-OLED with an improved singlet-excited energy transfer process from a sky-blue TADF assistant dopant (AD) (HDT-1) to a pure-blue terminal emitter (TE) (v-DABNA). Further, with sophisticated control of device architectures and materials combination, we report improved OLEDs.