2, Pohang University of Science and Technology, Pohang, , Korea (the Republic of)
Flexible plastic substrates have received attention as components in next-generation optoelectronic devices such as organic light-emitting diodes (OLEDs) and organic solar cells because of lightweight, inexpensive, and enable to roll-to-roll mass production. To improve the performance of devices based on flexible substrates, nano-structuring technology, which applies haze in substrate has become indispensable, because planar structure causes unwanted surface reflection and total internal reflection. Recently, there have been tremendous efforts to fabricate nanostructures on substrates such as low index-grid structure, refractive index modulation layer, micro-lens array attaching, and surface modulation including nanoimprinting, embedding scattering particles in film. However, the low index-grid structure requires high temperature process or acid treatment that can damage the polymer substrates. Also, micro-lens array attaching and the surface modulation techniques have complex fabrication process and reduce the total transmittance due to Fresnel reflection and light absorption. Therefore, the hazy substrate which is fabricated at low temperature and simple process is highly required.
In this work, we report the high haze film that manufacture scattering centers in which air is trapped in flexible film by coating a planarization layer on a micro-patterned substrate. Micro-patterns are formed on PET using AgCl nanorods as an etching mask and oxygen plasma treatment. Also, we can control the haze by changing the aspect ratio of micro-patterns to trap large air sites with plasma treatment time. After planarization treatment with colorless hybrid UV-curable polymer, Ormoclear, the average roughness of surface reduced 181 nm to 0.72 nm. The average haze from 0.9 % to 87.92 % has been achieved with the extremely flat surface. Also, the average transmittance has been enhanced from 89.84 % to 93.34 %. The finite-difference time-domain (FDTD) simulations was conducted to demonstrate that the air-trapped sites in the film can effectively extract light with wide angle distribution by inducing haze.