Using a multi-wavelength expansion of the Gerchberg-Saxton algorithm, a surface relief diffractive optical element (DOE) is designed, fabricated, and measured. Spectrum splitting capability of the designed DOE is 76.29% of an ideal rectangular spectral filter under plane wave illumination. The DOE is fabricated using grayscale lithography and measured under a solar simulator lamp. The spectral distribution of light across the PV plane is measured using a scanning spectrometer. Simulated 2-bandgap conversion efficiency for ideal silicon and indium gallium phosphide PV cells in this system is 31.61%, while conversion efficiency based on the measured DOE is 28.98%. The difference between simulated and measured results is based on several factors, including discrete Fourier analysis, divergent illumination, and fabrication error.