Improvement of color purity in white OLED based on Zn(HPB)2 as blue emitting layer

We synthesized zinc (II) [2-(2-hydroxyphenyl)benzoxazole] (Zn(HPB)2) as blue emitting materials and evaluated in the organic light emitting diodes (OLEDs). The layer of Zn(HPB)2 doped with 4-(dicyanomethylene)-2-t-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl)-4H-pyran (DCJTB) (Zn(HPB)2:DCJTB) as emitters has been demonstrated. The structure of the device is indium–tin–oxide (ITO)/N,N′-bis-(1-naphthl)-diphenyl-1,1′-biphenyl-4,4′-diamine (NPB, 40 nm)/Zn(HPB)2/Zn(HPB)2:DCJTB/Alq3 (20 nm)/LiF/Al. The thickness of Zn(HPB)2 layer was 0, 10, 20, 30 nm at the same time the thickness of Zn(HPB)2:DCJTB layer were 40, 30, 20, 10 nm. When thickness of Zn(HPB)2 layer was 30 nm and the thickness of Zn(HPB)2:DCJTB layer was 10 nm, white emission is achieved. The Commission Internationale de l'Eclairage (CIE) coordinates of the white emission are (0.304, 0.332) at an applied voltage of 10.5 V.