Planar ultrathin omni-directional perfect absorber utilizing amorphous silicon for photovoltaics

Abstract

Resonant plasmonic metasurfaces and thin film stacks have been extensively studied for spectral control and perfect absorption enhancement functionality. Essentially, the plasmonic nanostructures or metallic films enable the optical field resonant and confinement at the nanoscale, and thus yield the Ohmic heat absorption in the nanoscale metals. However, typical perfect absorbers based on film coatings are usually sensitive to the variation of large oblique incident angles, and mostly lack the capability for direct conversion to photocurrents and photovoltaics. Here, we proposed a lithography-free perfect absorber design consisting of metallic and amorphous silicon (α-Si) films with deep-subwavelength thickness (∼ λ/20 - λ/100). The perfect absorptivity spectrum enjoys Omni-directional optical characteristics, which remains the high absorption for the normal incidence to large oblique incidence angles of ± 60°. Due to the strongly trapped resonance in the Fabry-Perot cavity, the majority of light absorption (∼89%) takes place in the core α-Si layer, which could enable the potential optoelectronic conversion to photocurrents and photovoltaics. Our proposed perfect absorber based on ultrathin α-Si films enjoys the great simplicity of design and manufacturing and suggests a variety of promising applications, including photovoltaics, optical sensors, solar cells, photodetectors, thermal bolometers, nano-imaging devices, color filters, and thermal emitters, etc.