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Bifunctional Hybrid a-SiOx(Mo) Layer for Hole-Selective and Interface Passivation of Highly Efficient MoOx/a-SiOx(Mo)/n-Si Heterojunction Photovoltaic Device

Gao, Ming, Chen, Dongyun, Han, Baichao, Song, Wenlei, Zhou, Miao, Song, Xiaomin, Xu, Fei, Zhao, Lei, Li, Yonghua, Ma, Zhongquan
ACS applied materials & interfaces 2018 v.10 no.32 pp. 27454-27464
X-ray photoelectron spectroscopy, density functional theory, electrons, energy-dispersive X-ray analysis, indium, materials science, models, silicon, solar cells, tin, transmission electron microscopes
The promising n-Si-based solar cell is constructed for the purpose of realizing hole- and electron-selective passivating contact, using a textured front indium tin oxide/MoOₓ structure and a planar rear a-SiOₓ/poly(Si(n⁺)) structure severally. The simple MoOₓ/n-Si heterojunction device obtains an efficiency of 16.7%. It is found that the accompanying ternary hybrid SiOₓ(Mo) interlayer (3.5–4.0 nm) is formed at the MoOₓ/n-Si boundary zone without preoxidation and is of amorphous structure, which is determined by a high-resolution transmission electron microscope with energy-dispersive X-ray spectroscopy mapping. The creation of lower-oxidation states in MoOₓ film indicates that the gradient distribution of SiOₓ with Mo element occurs within the interlayer, acting as a passivation of silicon substrate, which is revealed by X-ray photoelectron spectroscopy with depth etching. Specifically, calculations by density functional theory manifest that there are two half-filled levels (localized states) and three unoccupied levels (extended states) relating to Mo component in the ternary hybrid a-SiOₓ(Mo) interlayer, which play the roles of defect-assisted tunneling and direct tunneling for photogenerated holes, respectively. The transport process of photogenerated holes in the MoOₓ/n-Si heterojunction device is well-described by the tunnel-recombination model. Meanwhile, the a-SiOₓ/poly(Si(n⁺)) has been assembled on the rear of the device for direct tunneling of photoinduced electrons and blocking photoinduced holes.