Fabrication and Spectral Characteristics of Silicon Nanowires for Efficient Solar Energy Harvesting

Abstract

Solar cell utilizes a small portion of solar spectrum leaving higher energy (> band gap, E_g) as thermalization loss and lower energy (< band gap, E_g) as absorption loss. Wavelength-sensitive engineered absorbing layer such as nanometric absorber holds huge potential in this context. Here in this work, a simple and hands-on strategy was devised to grow silicon nanowires (Si-NWs) on silicon wafer. Nanoparticles were achieved in the first step and used as seeds to directed growth of Si-NWs. As-grown Si-NWs with coverage ca. 6.5 × 10⁸/cm² were characterized through scanning electron microscope. To realize such Si-NWs as nanometric absorber in nanowire solar cell, a three-dimensional finite-difference time-domain simulation has been carried out. Considering the possibility of Si-NWs of different diameters as observed in experimental investigations, Si-NW of 50-, 100-, and 150-nm diameters was chosen in simulation. Two specific wavelengths, 700 and 1100 nm, were in prime focus to understand the characteristics of exciton generation within Si-NW. Confinement in exciton generation rate distribution at 700-nm solar spectrum for Si-NW of 150 nm was found to be most effective, whereas at 1100-nm wavelength Si-NW of 100 nm showed higher exciton generation rate distribution with the nanowire. Exciton generation line profiles along the center and edge were extracted, and comparative analysis was carried out for different diameters of Si-NW at 700- and 1100-nm wavelengths. Such experimental and correlated simulation is indispensable not only to reduce costs but also to understand and improve the cell efficiency using the light-trapping technique.