Deep-blue organic light-emitting diodes based on a doublet d – f transition cerium(III) complex with 100% exciton utilization efficiency

Compared to red and green organic light-emitting diodes (OLEDs), blue OLEDs are still the bottleneck due to the lack of efficient emitters with simultaneous high exciton utilization efficiency (EUE) and short excited-state lifetime. Different from the fluorescence, phosphorescence, thermally activated delayed fluorescence (TADF), and organic radical materials traditionally used in OLEDs, we demonstrate herein a new type of emitter, cerium(III) complex Ce-1 with spin-allowed and parity-allowed d–f transition of the centre Ce3+ ion. The compound exhibits a high EUE up to 100% in OLEDs and a short excited-state lifetime of 42 ns, which is considerably faster than that achieved in efficient phosphorescence and TADF emitters. The optimized OLEDs show an average maximum external quantum efficiency (EQE) of 12.4% and Commission Internationale de L’Eclairage (CIE) coordinates of (0.146, 0.078). A luminescent cerium(III) complex could be promising for realizing efficient and stable deep-blue organic-LEDs required for display and lighting applications, arising from its theoretical high exciton utilization efficiency and short excited-state lifetime. Liding Wang, Zifeng Zhao, and coworkers from China have shown that a new cerium (III) complex called Ce-1, which supports a d-f energy level transition, can efficiently emit blue light with a high photoluminescence quantum yield up to 93% and a short excited-state lifetime of 42 ns. OLEDs fabricated from the complex offered a maximum external quantum efficiency of 12.4% and a luminance of about 1000 cd m−2, and their emission is characterized as being deep blue with CIE colour coordinates of (0.146, 0.078).