Organic light-emitting devices (OLEDs) with the hole-blocking layer NaF between the alpha-naphthylphenyliphenyl diamine and ITO were fabricated using a vacuum evaporation method. Compared to the different thickness of the hole-blocking layer, the OLEDs with the 1.0 nm thickness layer showed the maximum efficiency. The enhancements in efficiency were resulted from an improved balance of hole and electron injections. After comparing different hole-blocking layer density, NaF was a good candidate for the hole-blocking layer, and 1.0-nm thickness NaF layer showed better operational durability and life. (c) 2006 Elsevier B.V. All rights reserved.