Improvement in Luminance Efficiency by Insertion of Buffer Layers in Flexible Organic Light-Emitting Diodes

摘要

This study employed poly(3,4-ethylenedioxy-thiophene):poly(styrenesulfonate) (PEDOT:PSS), 4,4′-bis[N-(1-naphthyl)-N-phenylamino]-biphenyl (α-NPD) and α-NPD/Teflon as buffer layers between the organic layer and indium tin oxide (ITO) of a flexible organic light-emitting diode (FOLED) to enhance the luminance efficiency of the device. PEDOT:PSS and α-NPD were spin-coated onto the ITO substrate, but α-NPD was first dissolved in chloroform. With the deposition of PEDOT:PSS of 40 nm thickness, the surface roughness of ITO decreased from 2.768 to 1.415 nm, whereas the luminance yield increased from 2.0 to 4.0 cd/A; the maximum luminance was 1500 cd/m~2 at 44mA/cm~2. With the deposition of α-NPD of optimum thickness as buffer layer, the device had a luminance yield of 5.2 cd/A and a maximum luminance of 1220 cd/m~2 at 25 mA/ cm~2. When the α-NPD buffer layer was further coated with a thin layer of Teflon by evaporation, i.e., α-NPD/Teflon (55/1 nm), the luminance yield of the device increased to 6.5 cd/A.