White organic light emitting devices with thin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) layer

In this letter, we have fabricated an efficient, color stable white organic electroluminescent device through the incorporation of double thin 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) emitting layers and 4,4′-bis[N-(1-naphthyl)-N-phenylamino]biphenyl (NPB), a hole transporting and blue emitting material. The device structure is ITO/NPB 45 nm/DCJTB 0.15 nm/NPB 5 nm/DCJTB 0.15 nm/BCP 10 nm/AlQ 50 nm/LiF 0.3 nm/Al 150 nm. This device exhibited a pure white-light emission having Commission Internationale de I’Eclairage (CIE) coordinates of (0.324, 0.336), a current efficiency of 2.9 cd/A and a maximum brightness of 7016 cd/m2. When the current density increased from 2 mA/cm2 to 100 mA/cm2, we observed only a slight shifting in the CIE coordinates from (0.324, 0.336) to (0.320, 0.326). Moreover, the efficiency of the device with double thin emitting layers of DCJTB is two times higher than the device with only one DCJTB layer.