This Conference Presentation, "Vibrant reflective structural colors with lossy metals using grating supermode resonances," was recorded at Photonics West 2020 held in San Francisco, California, United States.
Disordered photonic systems as observed in iridescent insects and flowers introduces new pathways for realizing cost-effective and scalable structural colors. In this work, we present a fast-colorimetric humidity sensor derived from a disordered arrangement of polydisperse nanoporous titania microspheres. The sensor relies on changes in the total scattering of the microspheres upon variations in the surrounding humidity. The incoherent scattering from each particle allows the sum of the individual cross sections to determine the total scattering cross section, which converts the individual noisy spectra to a smoothly varying spectrum that gives rise to a saturated color.[1] We show that because the titania microspheres is highly porous with 1~2 nm-sized nanopores, water can diffuse into the particle interior via intracrystalline dynamics, thereby changing the effective permittivity and consequently the scattered color at ultra-fast speeds (sub 50ms). Our results provide a practical route toward achieving cheap, simple, scalable, ultrafast colorimetric humidity sensors using structural colors from disordered nanoporous microspheres [2].
[1] Alam, A-M; Baek K; Son J; Pei Y-R; Kim D-H; Choy J-H; and Hyun J-K. Generating Color from Polydisperse, Near Micron-Sized TiO2 Particles, ACS Appl. Mater. Interfaces, 2017, 9 (28), 23941– 23948
[2] M-Noor, S; Jang, H ; Baek K; Pei Y-R; Alam, A-M; Kim,Y.H; Kim, I.S; Choy, J.H and Hyun J-K. Ultrafast humidity-responsive structural colors from disordered nanoporous titania microspheres. Submitted (2019)
Colorful semitransparent organic photovoltaic cells (OPVs) are increasing in demand due to their application in building-integrated photovoltaics. In general, the colors in OPVs have been determined by the absorption properties of the active material, requiring one to use different active materials to achieve distinct colors. However, such a strategy presents challenges in fabrication, costs and implementation as different processes are needed to produce differently colored OPVs. Moreover, the photovoltaic performance cannot stay uniform from different active materials in colored OPVs. In this work, we present a simple solution to such problems by incorporating transmissive Fabry-Perot-type color filters (CFs) as the electrode in an OPV employing one type of active material. From this modification, we achieve widely tunable colors covering the whole visible range with high spectral purity, peak transmission efficiencies surpassing 25% at the expense of charge generation that is only a fraction of that of an opaque OPV, and uniformity in device performance regardless of transmitted color. Because the CF is spatially removed from the charge generation and transport pathway, the optical characteristics are largely decoupled from the electronic characteristics. This provides one the freedom to explore creative designs without having to consider the electronic properties and uniformity in performance. Furthermore, integration of CFs into OPVs ensures the transmitted colors to be spectrally pure, bidirectional, and of high saturation represented by sub-100nm resonance widths, providing optical characteristics suitable for use in colorful power generating windows.
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