Blocking impurities in organic light emitting device by inserting parylene interlayer

Abstract

Secondary-ion mass spectrometry is used to study ion diffusion from a substrate into an organic film, which is considered as one of the reasons for organic-light-emitting-device degradation and instability. Results show that a 1 μm-thick parylene layer inserted between an indium-tin-oxide (ITO) anode and a soda-lime glass substrate effectively controls the diffusion of sodium, potassium, silicon and sulphur ions from the substrate to the device. The effect is the same as that in the case of using a plastic substrate which is sodium- and potassium-free. Also a 3 nm-thick parylene layer grown in between an ITO anode and a hole transport layer (HTL) not only shows improvement in device performance, but also is capable of blocking impurities such as sodium, potassium, silicon and sulphur ions. This study shows that the use of a parylene layer is effective for controlling contamination coming from the substrate. ©2005 The Japan Society of Applied Physics.