Angle-independent diffractive optical elements for efficient solar energy conversion

Conversion of solar energy into electricity is crucial to meet our ever-growing energy needs. The broadband spectrum of the sunlight limits the conversion efficiency of the single- and multi-junction based solar cells. Moreover, the angle of incident radiation dramatically decreases the amount of converted energy. In fact, diffractive optical elements (DOEs) designed for spectrally splitting solar light are optimized for normal incidence, and their performance drastically decreases under angled-illumination. Unfortunately, once the number of design parameters two of which are the number of wavelengths and number of incident angles increases, computational expense for DOEs design rises. Here we design DOEs which concentrate and split the broadband radiation under angled-illumination. In our design, we take thin, transparent and cost-effective materials into account, and we manage to disperse the broadband radiation 400 nm - 1100 nm into two separate bands which are the visible band 400 nm - 700 nm and the short-IR band 701 nm - 1100 nm. We observe that spectral splitting of the broadband light is less sensitive to variation of incident angle of solar radiation once DOE optimization performed for the area which is half of the output plane. As a result, 8% and 18% excess solar energy conversion can be achieved within the visible band and the short-IR band, respectively. What's interesting is that less than 0.6% deviation in output intensity can be observed when a single DOE is illuminated at angle spans from 0 to 80 degrees.