High performance non-doped blue-hazard-free hybrid white organic light-emitting diodes with stable high color rendering index and low efficiency roll-off

White organic light-emitting diodes (WOLEDs), for display and lighting applications, combine features such as high performance, high color quality, low efficiency roll-off and blue-hazard-free are extremely important. In this study, we manufactured a highly efficient bluish-green thermally activated delayed fluorescence (TADF) OLED. The maximum external quantum efficiency (EQE), power efficiency (PE), and current efficiency (CE) were 16.0%, 46.2 lm/W, and 45.9 cd/A, respectively. Next, a non-doped and blue-hazard-free hybrid WOLED was prepared by employing reasonably inserting several red and yellow ultra-thin phosphorescent emitters in between the bluish-green TADF emitters. The device showed a maximum EQE of 18.7% and a low EQE roll-off of 7%. At 1000 cd/m2, a high color rendering index (CRI) of 87 and a low correlated color temperature (CCT) of 2759 were obtained. The result showed that bluish-green TADF material has potential applications in healthy WOLEDs without blue-hazard. Also, the strategy of inserting several long-wavelength ultra-thin phosphorescent emitters in between bluish-green TADF emitters with bipolar transport characteristic, which can reduce efficiency roll-off and enhance device electroluminescence efficiency, was demonstrated.