Efficient Blue Phosphorescent OLEDs with Improved Stability and Color Purity through Judicious Triplet Exciton Management

Highly efficient and stable blue phosphorescent organic light-emitting diodes are achieved by employing a step-wise graded doping of platinum(II) 9-(pyridin-2-yl)-2-(9-(pyridin-2-yl)-9H-carbazol-2-yloxy)-9H-carbazole (PtNON) in a device setting. A device employing PtNON demonstrates a high peak external quantum efficiency (EQE) of 17.4% with an estimated LT₇₀ lifetime of over 1330 h at a brightness of 1000 cd m⁻². PtNON is then investigated as a “triplet sensitizer” in an alternating donor–acceptor doped emissive layer to further improve the device emission color purity by carefully managing an efficient Förster resonant energy transfer from PtNON to 2,5,8,11-tetra-tert-butylperylene as a selected acceptor material. Thus, such OLED devices demonstrate an EQE of 16.9% with color coordinates of (0.16, 0.25) and an estimated luminance (LT₇₀) lifetime of 628 h at a high brightness of 1000 cd m⁻².