Fabrication of diverse-scale patterned layer on organic photovoltaics

In order to increase the conversion efficiency of organic photovoltaics (OPV), diverse-scale patterns were formed on a glass substrate using the direct printing technique. The optical properties of the patterns depended on the size, shape, height, and pitch of the patterns. Randomly distributed nano- and micro-patterns caused light scattering, which increased the diffusion transmittance. The other pattern, which was a nanosized anti-reflective pattern comprising a 300nm sized hexagonal array, decreased the reflectance of light on the surface. The optical properties of these patterns, can be used to improve solar cell efficiency by increasing the light allowed onto the light-absorbing layer. We used a direct printing method with a poly(dimethylsiloxane) (PDMS) mold to fabricate these patterns on glass substrates. These patterns were transferred from PDMS to the surface of a glass substrate. Hydrogen silsesquioxane (HSQ) was used as a resin since its properties include volatility and allow for spincoating; it also has a reflective index similar to that of glass. This method has low cost and a simple process compared to optic-based lithography. After these patterns were formed outside the glass substrate, a conductive polymer layer and the active layer were formed by spin-coating, and the cathode was deposited by a thermal evaporator. The electrical properties of solar cells fabricated with these patterns on their surfaces were measured with a solar simulator. The conversion efficiency of the solar cells with these surface patterns showed an increase of up to 6.8% in comparison with conventional cells.