This study reports on the properties of organic light-emitting diodes (OLEDs) with zinc (II) [2-(2-hydroxyphenyl)benzoxazole] as a hole-blocking layer. OLEDs devices are prepared in a conventional OLEDs structure (i.e., anode/HTL/EL/HBL/cathode and anode/HTL/HBL/EL/ cathode). The luminescence efficiencies and the turn-on voltage are significantly affected by the existence of the hole-blocking layer. This is attributed to an excellent hole-blocking property, which is in turn due to the high HOMO energy level (6.5 eV). The device showed luminous efficiency 2.46 lm/W at 5 V The maximum luminance of about 10,000 cd/m(2) is obtained, and the turn-on voltage (2.5 V) is affected by the existence of the hole-blocking layer. (c) 2006 Elsevier B.V. All rights reserved.