Abstract
We present flexible transmissive structural color filters with high-color-purity based on a higher-order resonance suppression by inserting an ultrathin absorbing layer in the middle of a cavity. A 3rd order Fabry–Pérot (F-P) resonance, which exhibits a narrower bandwidth than a fundamental F-P resonance, is used to produce transmissive colors with an improved color purity. The thin absorbing layer is properly placed at a center of the cavity to highly suppress only a 5th order F-P resonance appearing at a short wavelength range while not affecting the 3rd order F-P resonance for color generation, thus being able to attain the high-color-purity transmissive colors without reducing a transmission efficiency. In addition, angle-insensitive properties are achieved by compensating a net phase shift with a dielectric overlay and using a material with a high refractive index for the cavity medium. Moreover, the transmissive colors on a flexible substrate are demonstrated, presenting that changes in both the resonance wavelength and the transmission efficiency are nearly negligible when the color filters are bent with a bending radius of 5 mm and over 3000 times bending tests. The described approach could pave the way for various applications, such as colored displays, decorative solar panels, and image sensors.
Highlights
Structural color filters, which selectively transmit or reflect a certain proportion of visible light by a physical interaction between light and nanostructures, have attracted substantial attention for their potential in achieving improved efficiency, easy scalability, high resolution, and high stability
Employing a 3rd order F-P resonance leads to a narrowband transmission in a spectral curve of transmittance as compared to a fundamental F-P resonance for achieving the high-color-purity transmissive colors, a 5th order F-P resonance appears at a short wavelength regime when the 3rd order F-P resonance is utilized for color generation, which significantly degrade the color purity
Thicknesses of the optimized dielectric overlays are found to be [55, 45], and 35 nm for the R, G, and B colors, respectively. 5 nm of Ge is inserted between two 70 nm (92 nm)-thick ZnS cavities in the middle for the B color (G color), while 13 nm of Ge is placed between two 112 nm-thick ZnS cavities for the R color
Summary
Structural color filters, which selectively transmit or reflect a certain proportion of visible light by a physical interaction between light and nanostructures, have attracted substantial attention for their potential in achieving improved efficiency, easy scalability, high resolution, and high stability. Employing a 3rd order F-P resonance leads to a narrowband transmission in a spectral curve of transmittance as compared to a fundamental F-P resonance for achieving the high-color-purity transmissive colors, a 5th order F-P resonance appears at a short wavelength regime when the 3rd order F-P resonance is utilized for color generation, which significantly degrade the color purity To address this challenge, the structural color filters are designed to have an electric field intensity profile with a maximum value of the 5th order resonance but a minimum value of the 3rd order resonance at the center of the cavity so that only the 5th order resonance is significantly suppressed without affecting the 3rd order resonance by introducing a lossy medium in a middle of the cavity. The present concept can be enabled by a simple deposition method, which can offer a key step toward the realization of the large-scale applications in a variety of research fields, including as e-paper display technologies, image sensors, flexible optoelectronic devices, and decorations
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