Ultrathin amorphous silicon thin-film solar cells by magnetic plasmonic metamaterial absorbers
Efficient solar harvesting for ultrathin amorphous silicon (α-Si) films with a thickness of less than 100 nm is critical to the performance of solar cells, since the very short carrier-diffusion length of α-Si and the Staebler–Wronski effect restrict their thickness. In this work, we numerically investigate energy harvesting in metamaterial-based solar cells, in which an ultrathin α-Si film is sandwiched between a silver (Ag) substrate and a square array of Ag nanodisks, and combined with an indium tin oxide (ITO) anti-reflection layer. It is found that only a 20 nm-thick α-Si film is able to absorb over 50% solar energy in the spectral range from 300 to 800 nm at normal incidence, and the amount of absorbed light is equivalent to a photocurrent of about 13.4 mA cm−2. This broadband absorption is achieved by the spectral design on the overlapped absorption peaks which are caused by the excitations of two lowest-order Fabry–Pérot (FP) resonances in the α-Si and ITO layers and a magnetic resonance arising from the plasmon hybridization between Ag disks and the substrate. The absorption performance of our structure is less dependent on the incident angle θ and polarization of light when θ < 20°, but it will decrease dramatically when θ > 70° (20°) for P (S) polarization.