Color-tunable organic light-emitting diodes with ultrathin thermal activation delayed fluorescence emitting layer

Recently, organic light-emitting diodes (OLEDs) are becoming increasingly attractive to information security, wearable healthcare, and other fields. These fields propose different requirements for performances of OLEDs, especially for voltage-controlled color tunability. In this study, it is proposed to use an ultrathin layer consisting of thermally activated delayed fluorescence (TADF) material as an emitting layer of OLEDs. On the one hand, compared to devices with an ultrathin phosphorescent emitting layer, the OLEDs with TADF show observable color-tunability. On the other hand, the color-tunable OLEDs with TADF show much higher efficiency than the color-tunable fluorescent OLEDs. It demonstrates that the reverse intersystem crossing process not only enhances the exciton utilization efficiency but also leads to an insufficient host-guest energy transfer. With this strategy, a color-tunable OLED is achieved with an external quantum efficiency about 8% and shows color variations over (0.04, 0.08) when its bias voltage increases from 4 to 8 V. By combining with a patterned mask technique, the color-tunable OLEDs can potentially be applied to the field of anti-counterfeiting and status lighting.