Semiperiodic Ultra-Broadband Double-Grating to Improve c-Si Thin-Film Solar Cell’s Optical Absorption, through Numerical Structural Optimization

Plasmonic gratings provide effective photon management techniques in thin-film solar cells, capable of extending the optical thickness of the solar cell’s active layer. However, the ultra-broadband nature of such application makes an optimal design of the grating structure quite challenging, since a fully periodic grating operates only in specific spectral ranges. To achieve a more broadband design, semiperiodicity is introduced, which, due to having controllable disorder, is an apt solution in broadband optical applications. In this work, semiperiodic double gratings as a broadband photon management technique are introduced in order to improve the optical absorption of c-Si thin-film solar cells, and optimized through numerical structural optimization. Physical parameters of both front and back gratings are determined taking the spectrally integrated optical absorption as the figure of merit and subsequently a semiperiodic double grating is established through adding defects to the fully periodic structure. It is shown that such semiperiodic structure is capable of enhancing the spectrally integrated optical absorption 88.6 % compared to a reference structure without gratings.