Selective absorption of a thermophotovoltaic cell using a thin semiconductor and a top fishnet-structured electrode

The electromagnetic field around a thermophotovoltaic (TPV) cell made of a metal–semiconductor–metal (MSM) multilayer with a square-grid electrode layer, referred to as a fishnet layer, was numerically calculated using a three-dimensional finite difference time domain method to obtain the absorptance of the MSM multilayer. In this study, gold and gallium antimony assumed to be materials of the metal and semiconductor layer, respectively. Even if there was no top metal layer, several peaks of absorptance were observed because of the optical interference inside the gallium antimony thin film. Here, the peak wavelength shifted to a shorter wavelength region by placing a fishnet layer on the gallium antimony layer. Moreover, the wavelength of the first peak of the optical interference could be adjusted at the active range of wavelength from 0.8 um to 1.8 um for the TPV cell made of gallium antimony for a practical power generation system. As a result, even in a several hundred nanometers thickness of semiconductor, a 60% of radiant energy absorbed could be concentrated in the active range of wavelength that is defined as a spectral efficiency. From the simulation results with an equivalent waveguide model, the shift of the first peak using the fishnet layer could be described using a dispersion relation of the waveguide, which was fulfilled with gallium antimony. Moreover, the superposition of different resonant modes originated from the waveguide-like structure and strip-wired structure affected the spectral absorption of the MSM multilayer when the wall of the fishnet structure was expanded.