Freeform surface relief diffractive optic for photovoltaic spectrum splitting

A surface relief diffractive optical element (DOE) for photovoltaic (PV) spectrum splitting is fabricated and tested. The optic is designed using a modified Gerchberg-Saxton algorithm. The module consists of a DOE followed by a 3.3 cm focal length lens. Alternating side-by-side PV cells - Indium Gallium Phosphide and Silicon - are placed at the collection plane. The DOE is fabricated in photopolymer using grayscale lithography. Optical efficiency and spectral distribution are measured with a scanning spectrometer. Two-bandgap conversion efficiency of 25.4% is achieved using the fabricated DOE. Simulations show that 28.4% conversion efficiency is possible with this type of optical element, which approaches the maximum possible conversion efficiency of the two-cell combination used (32.4%).