Optical design of selectively scattering nanostructures for angle sensitive semi-transparent photovoltaics

Semi-transparent photovoltiacs are of interest for improving integration of solar energy harvesting with architecture. However, the competing requirements of optical transparency and efficient absorption of the incident spectrum severely limit performance. To address this tradeoff, we propose an angle selective organic photovoltaic window structure, structured such that normally incident light is transmitted to maintain window-quality transparency, while direct sunlight at an elevated angle is targeted for absorption. The localized surface plasmon resonance properties of metal nanorods are employed for angle and spectrally dependant scattering. The optical interference patterns arising when light propagates through subwavelength planar dielectric stacks are engineered to optimize the optical mode created by the metal scatterers via an evolutionary algorithm. We numerically model the transmission and absorption performance of a thin semi-transparent organic photovoltiac film under angled solar illumination to evaluate the potential for the proposed design. An optimized selective structure can maintain 70% optical transparency at normal incidence while improving total absorbed power by a factor of 2.3 vs. a lone semi-transparent cell of comparable transparency.