Angle-Insensitive Transmission and Reflection of Nanopatterned Dielectric Multilayer Films for Colorful Solar Cells.

Aesthetically appealing photovoltaic (PV) panels with colorful layers are used in numerous applications involving color matching with the surroundings. To develop a colored film for a PV system, appropriate optical properties such as high transparency and low angle sensitivity are necessary because the colored layers can reduce the efficiency of the PV system by causing variations in the transmittance and angle of incidence. Herein, we propose a facile fabrication method for bioinspired three-dimensional (3D) photonic crystal (PC) films that exhibit broad angle-insensitive transmission and reflection, for application in colorful PV. This structure, patterned on a sequentially stacked 11-layer film of SiO2 and TiO2, is fabricated via nanoimprint lithography and a one-step dry-etching process, without using a metal mask. The changes in transmission and reflection are observed via ultraviolet-visible spectroscopy and from the reflected images obtained under various angles. The transmittance dips of the 3D PC film shift by less than 10 nm in wavelength, for angles from 0 to 45°, indicating low angle dependency. In addition, the change in the observed color, with respect to the viewing position, is less in the fabricated film. Once the 3D PC film was added to a commercial PV cell, it exhibited a higher efficiency (approximately 6% upper) when compared to a cell with a one-dimensional PC film, during the duration of the experiment, from 0 to 30°. Thus, the proposed method demonstrates excellent potential for developing structural color films for achieving aesthetically appealing PV cells.