The microstructure evolution during MoS2 films growth and its influence on the MoS2 optical-electrical properties in MoS2/p-Si heterojunction solar cells

Abstract

Abstract The microstructure of MoS2 films is crucial important for its photoelectrical properties, which has significant impact on its application in the field of photovoltaic devices. In this paper, a set of MoS2 thin films with varied thickness was prepared by magnetron sputtering. The influence of the MoS2 microstructure on its optical and electrical properties and, especially, the MoS2/p-Si solar cells photovoltaic performance was investigated in terms of thin films growth. The results reveal that, as the thickness increases, the microstructure of the MoS2 films evolves from amorphous to microcrystalline with the in-plane E2g1 and out-of-plane A1g Raman modes enhancing and the parallel (002) growth orientation increasing. The films electrical conductivity significantly improves owing to the enhanced MoS2 crystallinity. When the thickness is 10 nm, the small ordered MoS2 crystal clusters gradient distribute from the surface to the bulk in the films, contributing to the stress release in the amorphous precursor. Simultaneously, the optical band gap of the MoS2 films shows a maximum of 1.3 eV, due to the less band tail states in the films at the initial phase transition. The optimized optical-electrical properties of the MoS2 films lead to the reducing defects recombination and the enhanced carrier transportation at MoS2/p-Si interface, which promotes the rectification behavior of the pn-junction up to 102. Besides, the significant improvement of the photo-response in MoS2/p-Si heterojunction is obtained, especially in short wavelength range. Correspondingly, the photovoltaic characteristics (Voc, Jsc and FF) of the MoS2/p-Si solar cells increase, and thus an enhancement of the cells conversion efficiency is achieved with 10-nm MoS2 layer.