Achieving efficient and stable blue organic light-emitting diodes via suppressing triplet–polaron annihilation processes

Abstract

It is still challenging to achieve blue OLEDs with sufficient color purity, lifetime and efficiency for applications. Thermally activated delayed fluorescence (TADF) materials become the most promising. However, the internal mechanism of the efficiency roll-off and long-term stability degradation still needs deep research. In this work, the energy transfer and exciton quenching processes in TADF-based blue OLEDs were analyzed under steady-state conditions and their relative contributions to efficiency roll-off were quantified. Furthermore, the degradation mechanism in the TADF-based blue OLEDs was investigated both theoretically and experimentally by a comprehensive exciton quenching model. It was demonstrated that suppressing the triplet–polaron annihilation processes and reducing the accumulation of triplet excitons through reasonable energy transfer can decrease the effect of exciton quenching, thereby significantly reduce the efficiency roll-off and improve device lifetime. It can be seen that the external quantum efficiency (EQE) of the resulting blue OLEDs was enhanced to 30.3 % with CIE coordinates of (0.16, 0.25) and kept 20.9 % at the luminance of 1000 cd/m2. More importantly, the device lifetime was also significantly enhanced, which is over three times longer than that of the unoptimized devices due to the suppress of triplet-polaron annihilation and triplet accumulation.