Extending the near-infrared band-edge absorption spectrum of silicon by proximity to a 2D semiconductor

Because of its low-cost, silicon is the standard material for photovoltaic conversion. Yet, its band-edge absorption spectrum is narrower than the spectrum of the solar radiation, which reduces its conversion efficiency. In this paper, it is shown that the spectrum of absorbance of silicon can be extended to longer wavelengths by proximity to a two-dimensional (2D) semiconductor. Photo-induced Hall effect, together with standard absorption spectroscopy, was employed to estimate the increase of photo-conversion efficiency of a 2D-platinum-diselenide/intrinsic-silicon heterostructure. The system shows a significantly higher absorption in the infrared as compared to the single films. Angle resolved X-ray Photoelectron Spectroscopy (XPS) confirm that a change of the band structure occurs in the silicon substrate at the interface between the two semiconductors. The results are interpreted in the framework of band-gap narrowing due to hole-confinement in the Si, induced by electron-confinement in the 2D film. This allows us to claim that the increase of photo-conversion efficiency in the Pt/PtSe2/Si sample is due to an enhancement of the light absorbance of silicon near the interface. Possible application of the effect in photo-voltaic cells is discussed.