• Energy Research

Abstract Monolayer and few-layer two-dimensional (2-D) transition metal dichalcogenides (TMDs) such as molybdenum disulfide (MoS2) demonstrate excellent semiconducting and optical properties that have made them promising candidates for optoelectronic applications. However, fabricating high-quality and highly uniform MoS2 nanofilms on a large surface area remains a challenge. In this study, an effective synthesis method for large surface area of 2 cm by 2 cm, ultrathin MoS2 nanofilms using direct sulfurization of annealed molybdenum (Mo) foil was tested. Because of the unique band structure, the MoS2 layer not only serves as a carrier transport layer but also as an effective blocking layer for the diffusion of photo-generated holes. By optimizing the structural characteristics of MoS2 nanofilms, a dramatic increase in photovoltaic performance was measured as high as 11.2% in the novel graphene/MoS2/n-Si (G/MoS2/n-Si) Schottky junction solar cells. Our approach offers guidance to the synthesis of large surface area, ultrathin MoS2 nanofilms and furthers their appeal for use in highly efficient solar cell technologies.

The silicon vertical multi-junction (VMJ) solar cell has low costs and low series resistance, thus it has a good potential in concentration photovoltaics. However, there were few discussions about the thermal and electrical performance of silicon VMJ cell under non-uniform illumination. In this work, the thermal performance of silicon VMJ cell under 1D non-uniform illumination of 500 suns was calculated using finite element method first, and then the electrical performance of the cell was calculated using SPICE software based on the thermal simulation results. It was found that the mean temperature of the cell increased with the degree of non-uniform illumination when the area ratio of the sink to the cell was 500X, and the mean temperature changed few when the area ratio was 2500X. The efficiency of the cell did not decrease with the increase of the degree of non-uniform illumination when the area ratio was 500X, and the efficiency increased with the degree of non-uniform illumination when the area ratio was 2500X. Thus, the silicon VMJ cell had better performance than silicon planar junction cell under 1D non-uniform illumination of 500 suns.

Abstract Boron doped nc-Si:H/a-SiC:H quantum dot superlattice (QDSL) has a great potential to improve thin film silicon solar cells performance for high conductivity, wide band gap and anti-reflection effect. In this study p-type nc-Si:H/a-SiC:H QDSL has been fabricated by in situ grown method without subsequent annealing treatment. High resolution transmission electron microscopy and PL peak energy shift indicate that this method provides the possibility to precisely control the size of silicon quantum dots and the passivation at well/barrier interface. By optimizing structural characteristics and interface passivation, high perpendicular conductivity and strong anti-reflection effect was simultaneously obtained in QDSL films. An initial efficiency of 10.5% was achieved for n-i-p type hydrogenated amorphous silicon solar cell, which may guide further efforts arising the structure engineering of nc-Si:H/a-SiC:H QDSL for high efficient solar cells.

Abstract The isolation of two-dimensional (2D) materials and the possibility to assemblage as a vertical heterostructure have significantly promoted the development of ultrathin and flexible devices. Here, we demonstrate the fabrication of high efficiency graphene/MoS2/Si Schottky barrier solar cells with Molybdenum disulfide (MoS2) interlayers. MoS2 monolayers were prepared by sulfurizing pre-annealed molybdenum foil, which allows not only to precisely control the layer number, but also the nondestructive transference onto arbitrary substrates. The inserted MoS2 layers function as hole transport layer to facilitate the separation of electron-hole pairs as well as electron blocking layer to suppress the recombination at graphene/silicon interfaces. By optimizing the thickness of MoS2 layers, a high photovoltaic conversion efficiency of 15.8% was achieved in graphene/MoS2/Si solar cells. This study provides a novel approach for the synthesis of large-area MoS2 monolayers and their potential application for ultrathin and low-cost photovoltaic devices.