Fig. 2

Appearance and optical characteristics of the proposed thin film-based CRC. a Appearance of the CRCs. The color filters on the first BK7 glass substrates are optimized to exhibit distinct colors. b Measured specular/diffuse reflection of Sample #5 in the wavelength range of 400–700 nm. c Digital photographs of Sample #4 captured from viewing angles ranging from 0° to 55°, and the proposed CRC exhibits outstanding angle-independence within ± 50° viewing angles. d Total reflection of Sample #5 in ultraviolet–visible-near infrared range (300–2500 nm). The AM1.5 solar spectrum (the light yellow area) is plotted for reference. e The reflection/absorption of the bare BK7 glass substrate and the designed/measured reflection/absorption of the proposed CRC in the wavelength range of 3–20 μm. The atmosphere transparency window (the light blue area) is plotted as reference. f The proposed CRC fabricated on a flexible PC substrate