Effects of different buffer layers in flexible organic light-emitting diodes Original Research Article

In order to improve the luminance efficiency and flexibility of flexible organic light-emitting diodes (FOLEDs), a buffer layer was inserted between ITO and hole transport layer by spin coating. The buffer layer employed is poly(3,4-ethylene dioxythiophene):poly(styrene sulfonate) (PEDOT:PSS), PEDOT:PSS/Teflon, N,N′-bis-(3-methylphenyl)-N,N′-bis-(phenyl)-benzidine (TPD) or bis[N-(1-naphthyl)-N-phenyl]benzidine (α-NPD). The TPD and α-NPD were first solved in chloroform before spin coating. When 40 nm PEDOT:PSS was employed as buffer layer, the FOLED luminance efficiency increased from 2 to 4 cd/A in comparison with the original device without any buffer layer. If the buffer layer was PEDOT:PSS/Teflon, the luminance efficiency increased slightly to 4.4 cd/A. If α-NPD buffer layer was used, the luminance yield of the FOLED could be increased to levels ⩾5.5 cd/A.