Reduced Reflection in polycrystalline silicon thin films through ion implantation induced surface textures and deposition of silver nanostructures

Abstract

This work investigates a novel method to enhance light trapping within polycrystalline silicon (poly-Si) thin films for photovoltaic applications. The method combines the use of hydrogen ion implantation for creation of surface textures in poly-Si thin films and the deposition of silver nanostructures on the textured surface. Poly-Si thin films were prepared by solid phase crystallization of amorphous silicon (a-Si) layer deposited on a SiO₂/Si substrate. The a-Si was annealed at various temperatures 600 -1050 °C for 48 hours to grow grains of different size in p-Si, as confirmed by x-ray diffraction (XRD) measurements. These samples were then implanted with 20-keV hydrogen ions to a dose of 10¹⁷/cm², and some with an additional implant with 90-keV argon ions to a dose 5×10¹⁵ /cm². Following implantation, these samples were annealed in an Ar ambient at different temperatures. Surface blistering effects were observed using an optical microscope. Optical specular reflection measurements in the spectral range 400-1100 nm indicated that the reflectance of the samples with higher blistering had decreased remarkably from 40% to 10%. Lastly, the poly-Si samples with various textures were deposited with silver thin film followed by annealing in nitrogen ambient for forming Ag nanostructures on textured poly-Si surfaces. Scanning Electron Microscope (SEM) was used to image the surface structures. The formation of Ag nanoparticles on the poly-Si surface, with textures created by implantation followed by low-temperature annealing (e.g., 400 °C), can significantly reduce light reflection as opposed to the case with Ag nanoparticles formed on an un-textured, poly-Si surface.