Light out-coupling enhancement of organic light emitting devices using nano-structured substrate produced by rapid thermal processing

Abstract

We report significant enhancement in light out-coupling efficiency of organic light-emitting devices (OLEDs) using a nano-structured substrate by rapid thermal processing (RTP). On the backside of the indium tin oxide (ITO) coated glass substrate a thin film of magnesium fluoride (MgF2) was coated by thermal evaporation. Nano-structured films of MgF2 and ITO were then produced by RTP on both sides of the glass substrate. Bottom-emitting OLEDs were fabricated on the ITO-coated glass substrate with α-NPD as the hole transport layer, Alq3 as the emissive layer, and LiF and aluminum as the cathode. On the backside of the glass substrate nano-structured MgF2 were fabricated by RTP. Experimental results of enhancement of electroluminescent intensity (EL) with and without nano-structured films are presented. Results of EL intensity of OLED are also compared with the uniform MgF2 film coated on the backside of the substrate. It was found that the enhancement of EL intensity is much higher in the case of nano-porous MgF2 film than in the case of uniform MgF2 coated on the backside of the glass substrate.