Effect of doping-induced defect concentration on the characteristics of Si-quantum-dot solar cells

Abstract

A promising method to overcome the efficiency limit of the crystalline Si solar cell is to utilize the visible light in the solar-energy spectrum. Silicon quantum dots (QDs) have been proposed as a source of strong light emission in the visible range based on the quantum confinement effect [1–3]. Light emission in the full visible range of wavelength has been reported by controlling the size and the density of Si QDs embedded within various types of insulating matrix [2, 4]. The increased bandgap energy of Si QDs enables the light absorption in the visible range of the terrestrial solar spectrum. [5]. Formation of p-n junction by doping of n- or p-type impurities into Si QDs is a key process to form all-Si-QD active layers in photovoltaic devices. A Si-QD solar cell with an energy-conversion efficiency of 10.6 % has been developed by forming phosphorus-doped Si-QD superlattices (SLs) on a p-type crystalline silicon substrate for an active heterojunction layer [6, 7]. In this study, we fabricate B-, P-, and Sb-doped p- and n-type Si QDs/SiO 2 superlattices (SLs) for solar cells. We characterize the variations of defect concentrations due to doping by photoluminescence (PL) and thermally-stimulated current, and compare them with the photovoltaic characteristics of the solar cells.