Investigation in feasibility of Molybdenum as a back contact layer for Silicon based quantum dot solar cells

Abstract

A vertical structure with a back contact layer is suggested for silicon quantum dots (Si QDs) solar cells to overcome the current crowding effect arising from the high lateral resistance in the emitter layer of the existing mesa-structured Si QDs solar cells on quartz substrates. Molybdenum (Mo) is widely used as the back contact layer in CIGS solar cells due to its high electrical conductivity, good optical reflectance and chemical stability. This paper will focus on the feasibility of Mo as a back contact layer deposited between a quartz substrate and a sputtered silicon rich oxide (SRO) bilayers structure to obtain a fully vertical Si QDs solar cell. In this structure, the desired previously mentioned electrical and optical properties of the Mo thin film have to be maintained during and after a high temperature annealing process. This high temperature process is unavoidable in this structure as it is required to form the Si QDs. This paper aims to study factors that have impacts on critical properties of the Mo thin films processed in contact with Si and SiO₂ at high temperatures. Characterizations including film thickness, microstructure, sheet resistance and optical reflectance measurements are also performed. Furthermore, interfacial properties between the Mo layer and the upper SRO bilayers are investigated.