Ultrathin amorphous silicon thin-film solar cells by magnetic plasmonic metamaterial absorbers

摘要

Efficient solar harvesting for ultrathin amorphous silicon (alpha-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 alpha-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 alpha-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 alpha-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-Perot (FP) resonances in the alpha-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 theta and polarization of light when theta < 20 degrees, but it will decrease dramatically when theta > 70 degrees (20 degrees) for P (S) polarization.