Optical bandgap tuning of ICPCVD-made silicon nanocrystals for next generation photovoltaics

Superior optical properties of Si-Nanocrystals (Si-NCs) compared to bulk Si, particularly tunability of bandgap by controlling size, can be exploited for realizing next generation “all-Si” tandem solar cells [1]. In this study, we present optical bandgap tunability of Si-NCs made by Inductively Coupled Plasma Enhanced Chemical Vapor Deposition (ICPCVD) using SiO₂/SiO_x superlattice approach [2]. Deposition time of SiO_x sublayer, and hence the related thickness (T_SRO), was used as a variable parameter to realize Si-NCs of varying sizes. All multilayer (ML) samples were subsequently furnace annealed at 900°C, to allow for Si-NC formation. Formation of Si-NCs was confirmed by Raman spectroscopy. Transmittance, reflectance and absorptance spectra indicated gradual increase of bandgap with decreasing T_SRO. Optical bandgap, E_Tauc, estimated using Tauc analysis showed an increase in optical bandgap from 1.45 eV to 2.5 eV, as T_SRO was varied from 10 nm to 2 nm respectively.