Abstract: The present invention relates to a method for fabricating a sub-wavelength structure layer, including: forming a metal film on a passivation layer, an n-GaN layer or a transparent conductive oxide layer; performing thermal treatment to form self assembled metal nano particles; using the metal nano particles as a mask to remove a partial area of the passivation layer, the n-GaN layer or the transparent conductive oxide layer to form a sub-wavelength structure of which the cross-sectional area increases along the thickness direction of the passivation layer, the n-GaN layer or the transparent conductive oxide layer; and removing the metal nano particles. In addition, the present invention further provides the obtained sub-wavelength structure layer and a photoelectric conversion device using the same.