Transparent SiON/Ag/SiON multilayer passivation grown on a flexible polyethersulfone substrate using a continuous roll-to-roll sputtering system
© Kim and Cho; licensee Springer. 2012
Received: 9 September 2011
Accepted: 5 January 2012
Published: 5 January 2012
We have investigated the characteristics of a silicon oxynitride/silver/silicon oxynitride [SiON/Ag/SiON] multilayer passivation grown using a specially designed roll-to-roll [R2R] sputtering system on a flexible polyethersulfone substrate. Optical, structural, and surface properties of the R2R grown SiON/Ag/SiON multilayer were investigated as a function of the SiON thickness at a constant Ag thickness of 12 nm. The flexible SiON/Ag/SiON multilayer has a high optical transmittance of 87.7% at optimized conditions due to the antireflection and surface plasmon effects in the oxide-metal-oxide structure. The water vapor transmission rate of the SiON/Ag/SiON multilayer is 0.031 g/m2 day at an optimized SiON thickness of 110 nm. This indicates that R2R grown SiON/Ag/SiON is a promising thin-film passivation for flexible organic light-emitting diodes and flexible organic photovoltaics due to its simple and low-temperature process.
Rapid progress in organic-based flexible optoelectronics such as flexible organic light-emitting diodes [OLEDs] and organic photovoltaics [OPVs] required a high-performance thin-film passivation because both lifetime and performance of the flexible OLEDs and OPVs are critically affected by the quality of the encapsulation [1–3]. The long-term stability of flexible OLEDs and OPVs is still limited due to the instability of the luminescent organic materials and low work function metals, interfacial reactions, and chemical reactions of the organic layers with oxygen and moisture in air . For those reasons, several types of encapsulation techniques have been extensively explored to improve the long-term stability of flexible OLEDs or OPVs. In particular, thin-film passivation has been considered as the most desirable encapsulation for flexible OLEDs and OPVs due to its simplicity, thinness, and flexibility. Although various SiNx, SiOx, SiOxNy, AlOx, and Al2O3:N films have been reported, a single-layer-based thin-film passivation is not sufficiently dense to protect flexible optoelectronic devices from permeation by moisture and oxygen [5–9]. Therefore, multilayer passivation, such as Barix coating or NONON (SiNx/SiO2/SiNx/SiO2/SiNx) structures, has been proposed as a means to achieve ultra high barrier properties for flexible OLEDs or OPVs [10, 11]. However, Barix coating or the NONON structure still has not been employed in mass production of OLEDs due to its complicated process and long process time. We also reported that Al2O3/Ag/Al2O3 multilayer thin-film passivation has a high transmittance of 86.44% and a low water vapor transmission rate [WVTR] due to the SPR effects of the Ag interlayer and the effective multilayer structure that prevent the intrusion of water vapor . In a multilayer barrier, control of the Ag thickness is very important because the antireflection effect for high transparency is critically dependent on the thickness and morphology of the inserted Ag layer. However, a roll-to-roll [R2R] sputter-grown silicon oxynitride/silver/silicon oxynitride [SiON/Ag/SiON] multilayer has not been investigated for thin-film passivation even though it has various advantages such as high transparency and possibility of a simple R2R process.
In this work, we report on the characteristics of SiON/Ag/SiON multilayer passivation grown on a flexible polyethersulfone [PES] substrate using a specially designed R2R sputtering system. Optical, structural, and surface properties of the R2R-grown SiON/Ag/SiON multilayer were investigated as a function of the SiON thickness. Despite the low process temperature used, a SiON/Ag/SiON multilayer passivation showed a low WVTR of 0.031 g/m2 day and a high transmittance of 87.7% at an optimized SiON thickness of 110 nm.
Results and discussion
SiON/Ag/SiON multilayer passivation prepared by continuous R2R sputtering was investigated as a function of the top and bottom SiON thickness. The SiON/Ag/SiON multilayer thin-film passivation on the PES substrate has a high transmittance of 87.7% and a low WVTR due to the antireflection and surface plasmon effects of the Ag interlayer and the effective multilayer structure that prevent the intrusion of water vapor. At a SiON thickness of 110 nm, the R2R-grown SiON/Ag/SiON multilayer showed a WVTR value of 0.031 g/m2 day. These findings indicate that R2R-grown SiON/Ag/SiON is a promising thin-film passivation for flexible OLEDs and OPVs due to its simple and low-temperature process.
This research was supported by the Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education, Science and Technology (2010-0015596) and partially supported by Gyeonggi-do International Collaborative Research Program.
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