Reflective and transparent diffractive optical elements and their angular response

Improving solar cell efficiency has been a primary focus in achieving cost-effective and efficient solar cells, fulfilling space requirements and reducing environmental footprints. Of the various techniques available to improve the efficiency of solar cells, integrating diffractive optical elements (DOEs) with multi-junction solar cells has gained significant attention as a promising solution. However, DOEs are designed and optimized to operate under a fixed incident angle, hindering their use in solar cell applications. Therefore, the design of dedicated angle-independent DOEs capable of simultaneously splitting and concentrating sunlight (SpliCons) is paramount for the solar energy industry. In this thesis we used a significantly fast experimental approach to spectrally split and concentrate broadband light using SpliCons operating under angled illumination. In our experimental setup, a phase-only spatial light modulator (SLM) is used to emulate the SpliCons, where the thickness variations in the SpliCon are mimicked by controlling and modifying the gray levels in the SLM. The broadband spectrum is split and concentrated in the regions that are chosen for red (560-875 nm), green (425-620 nm), and blue (420-535 nm) wavelengths. We obtain 58%, 51% and 59% spectral splitting ratios with an enhancement factor of 202%, 188% and 204% for red, green, and blue channels, respectively. Experimentally, we show that the angle response of our angle-independent SpliCon is enhanced by 4.8 times which is limited by the acceptance angle of our setup. We further calculated the angle response of our SpliCon design using convolution method and show the angle independency of spectral splitting and concentration over a ±40° span. A proof-of-concept SpliCon has been fabricated by stereolithography additive manufacturing method using an ultra-clear resin with a refractive index of 1.45, closely resembling that of glass. The fabricated SpliCons have been tested under angled illumination, and their angular response is studied. Test results have revealed a successful angle-independent simultaneous splitting and concentration of the broadband light, validating the concept. The designed SpliCons represent a significant advancement toward the feasibility of building-integrated solar cells by enhancing tolerance to variations in the incident angle of sunlight, thereby improving overall energy capture and efficiency.