Structural and light trapping properties of nanoporous silicon micro-pyramid patterns encrusted with silver nanoparticles

Abstract

Surface modification to improve light trapping properties is one of the choices that can be used to improve the efficiency of silicon (Si)-based solar cells. In this work, a simple combined treatment is used to modify Si surfaces to improve their overall light trapping properties. Silver (Ag) nanoparticles were deposited on porous-Si micro-pyramid structures to investigate the effects of combining the three mechanisms on light trapping properties of the treated-Si surfaces. The surface modifications were introduced for a simple large-scale chemical treatment of the Si surfaces. It was found that the etching current is a limiting factor that controls the size of the etched nanopores. The size of the deposited-Ag nanoparticle depends on both the nanopore sizes of the porous pyramids and on the AgNO3 dipping time. The average Ag particle size increased from 20.5 nm, for samples with smaller nanopores etched with 10 mA/cm2 current, to 24.0 nm for samples with larger nanopores etched with 20 mA/cm2 current. From scanning electron microscopy (SEM) and as verified by X-ray diffraction (XRD), the average Ag particle size increased from 48.25 nm to about 64.09 nm as the AgNO3 dipping time increased from 10 to 40 min. The reflectivity measurements showed a considerable 98.44% reduction in the average reflectance of the treated samples in the wavelength range of 400–840 nm. It is believed that the Ag nanoparticles’ plasmonic behavior and the nanoporous pyramid patterns are responsible for this substantial reflectivity reduction which leads to an increased efficiency of light trapping of the treated-Si samples.