We studied the post annealing effect on the interface morphology and performance of organic light-emitting diodes (OLEDs) at 80 degrees C substrate temperature. We observed the crystallinity and roughness changes of each layer in an OLED with ITO/CuPc/NPB/Alq(3)/Al structure at various heat-treatment steps by X-ray diffraction (XRD) and atomic force microscopy (AFM). The roughness changes of each layer affected the current-voltage-luminance (IVL) characteristics of the OLEDs. The best annealing step with the best current efficiency was the sample with annealing at 80 degrees C for 2 h after the deposition of all organic layers. (C) 2012 Elsevier Ltd. All rights reserved.