Construction of High‐Quality Cu(I) Complex‐Based WOLEDs with Dual Emissive Layers Achieved by an “On‐and‐Off” Deposition Strategy

Abstract Inexpensive and highly luminescent Cu(I) complexes exhibit great potential as emitters in organic light‐emitting diodes (OLEDs), especially in white OLEDs (WOLEDs). In this work, two compounds 9‐(3‐(quinolin‐4‐yl)phenyl)‐9H‐carbazole (CzPQ) and 9,9′‐(quinoline‐4,6‐diylbis(3,1‐phenylene))bis(9H‐carbazole) (2CzPQ) are designed and synthesized to form Cu(I) complexes in situ by codeposition with copper iodide (CuI). The corresponding OLEDs show an orange red emission with a maximum external quantum efficiency (EQE) of 6.7%. Based on this result, an “on‐and‐off” strategy is proposed to achieve WOLEDs with the combination of Cu(I) complex layer and the pure ligand layer by controlling the shutter of CuI source on and off. The optimized WOLEDs give a maximum EQE of 2.4% with excellent Commission Internationale de L'Eclairage (CIE) coordinates of (0.32, 0.33) and a remarkable color‐rendering index (CRI) of 94. It can be forecasted that the device efficiency would be improved by tuning the chemical structure of the ligand.