Engineering Color and Angular Stability in Building-Integrated Photovoltaics Using Metal-Oxide Photonic Glasses

Abstract

Coloring building-integrated photovoltaics poses a dilemma: absorptive pigments cost photocurrent, while ordered photonic structures are iridescent. Amorphous photonic glasses, disordered packings of high-index nanospheres, are proposed to avoid both, yet their angle-independent color has rarely been quantified on a realistic module stack. A non-absorbing scatterer needs a high index with visible transparency, which the Moss rule caps near 2.35. Coupling Mie scattering, the Percus-Yevick structure factor, the exact phase function, and two-flux transfer with absorption and refraction at the front glass, we fix four target colors that a crowd-sourced naming survey calls unambiguously blue, green, gold, and terracotta, and map the recipes reaching them across four metal oxides, four encapsulants, two cell technologies, and wide ranges of particle size, packing fraction, and layer number. All four are reached in a laminated three-layer coating, to within DeltaE00 of 0.8 to 2.5, but not from one oxide: transparent TiO2 renders the blue and only pale warm tones; the green, gold, and terracotta require the blue-band absorption of V2O5, and the low-contrast oxides turn grey at the warm end. The encapsulant governs the color, and the cell technology does not. Disorder does not confer angle independence: the colors hold for an observer moving under a fixed sun but drift by DeltaE00 of 5 to 18 over the day, terracotta least, and a facade lit from above and viewed from below shifts every color towards the blue. Oxide, layer number, and facade geometry must therefore be designed together.