  Broadband absorption in the visible spectrum is essential in optoelectronic
applications that involve power conversion such as photovoltaics and
photocatalysis. Most ultrathin broadband absorbers use parasitic plasmonic
structures that maximize absorption using surface plasmons and/or Fabry-Perot
cavities, which limits the weight efficiency of the device. Here, we show the
theoretical and experimental realization of an unpatterned/planar semiconductor
thin-film absorber based on monolayer transition metal dichalcogenides (TMDCs).
We experimentally demonstrate an average total absorption in the visible range
(450 nm - 700 nm) of > 70% using > 4 nm of semiconductor absorbing materials
scalable over large areas with vapor phase growth techniques. Our analysis
suggests that a power conversion efficiency (PCE) of 15.54% and a specific
power > 300 W g^-1 may be achieved in a photovoltaic cell based on this
metamaterial absorber.
