Pure and stable top-emitting white organic light-emitting diodes utilizing heterojunction blue emission layers and wide-angle interference

In top-emitting white organic light-emitting diodes (TWOLEDs), it is usually difficult to realize a good chromaticity due to the strong suppression on the blue emission induced by the microcavity effect. In our work, the blue emission layer (EML) is located near the hole transport layer and the reflective anode to strengthen the wide-angle interference on the blue emission and enhance the output of light. Then we utilize the dual blue EMLs based on an electron-rich heterojunction to constrain most of the excitons in the blue EMLs. With the above two strategies, the intensity of the blue emission is significantly enhanced accompanying the chromaticity improvement in white emission. Some key factors including exciton distribution, energy transfer, and carrier trapping are analyzed to design the structure of the EMLs to acquire the pure and stable white emission. The excellent color stability with a Commission International de L'Eclairage (CIE) coordinate drift of only (0.009, 0.001) in the luminance range of 10-10⁴ cd/m² is obtained in our optimized TWOLED. The TWOLED also shows the high performances with a maximum luminance of 15360 cd/m², the CIE coordinates of (0.33, 0.41), and a current efficiency of 13.3 cd/A.