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

Abstract

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 Si02/SiOx superlattice approach [2]. Deposition time of SiOx sublayer, and hence the related thickness (TSRO), 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 Ts RO. Optical bandgap, ETauc, estimated usingTauc analysis showed an increase in optical bandgap from 1.45 eV to 2.5 eV, as TSRO was varied from 10 nm to 2 nm respectively.