Post-annealing effect on the interface morphology and current efficiency of organic light-emitting diodes

We studied the post annealing effect on the interface morphology and performance of organic light-emitting diodes (OLEDs) at 80 °C substrate temperature. We observed the crystallinity and roughness changes of each layer in an OLED with ITO/CuPc/NPB/Alq3/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 °C for 2 h after the deposition of all organic layers.

► We studied the post annealing effect on each layer of OLEDs on the surface roughness.
► We observed the crystallinity and roughness changes of each layer in an OLED.
► The roughness changes affected the current–voltage–luminance characteristics of the OLED.
► The annealing step was treating with the 80 °C for 2 h after all evaporation steps.