Synthesis Of MoSe₂ And Its Application In Silicon-based Solar Cells

In recent years,due to their excellent optoelectronic properties,two-dimensional materials have shown great research value and application potential in the field of optoelectronic devices.As a two-dimensional transition metal sulfide material(TMDCs),molybdenum diselenide(MoSe2)has optoelectronic properties comparable to graphene.More importantly,the appropriate band gap width(1.55 eV)and adjustable band gap make it widely used in the fields of optoelectronic devices,diodes,and photovoltaics.Silicon-based heterojunction solar cells with MoSe2 as the active layer are of great significance in the development of low-cost,high-efficiency,and highly flexible photovoltaic devices.This thesis starts with the synthesis of MoSe2 by chemical vapor deposition,and the application of MoSe2 in the field of silicon-based solar cells is explored in-depth through a combination of experiments and simulation.The main research contents are as follows:(1)Preparation of the MoSe2 film on the SiO2/Si substrate by a chemical vapor deposition method.The effects of different experimental process parameters(hydrogen participation,selenium source temperature,molybdenum source temperature,growth time,carrier gas flow rate,and hydrogen ratio)on the MoSe2 film were explored.In combination with the comprehensive analysis of XRD,SEM,Raman spectroscopy and other measurements,the optimized experimental parameters determined are molybdenum source temperature of 800℃,selenium source of 20 cm away from molybdenum source,growth time of 10 min,carrier gas flow rate of 60 sccm,hydrogen ratio of 10%.Under the optimized experimental parameters,a single-phase MoSe2 film with a band gap of about 1.25 eV and a thickness of about 255 nm was successfully synthesized.(2)The MoSe2 film was successfully transferred from the SiO2/Si substrate to the silicon substrate by wet chemical transfer to construct a MoSe2/Si heterojunction solar cell.The open circuit voltage,short circuit current density,fill factor and photovoltaic conversion efficiency of the solar cell are 0.19 V,5.71 mA/cm2,30.47%and 0.33%respectively.The lower performance of the device is analyzed in terms of film quality,electrode contact,and interface conditions.(3)Application of the AFORS-HET software to perform numerical simulation on MoSe2/Si solar cells.Aiming at the cell performance affecting factors in the experiment,the influence of the MoSe2 band gap width,back electrode work function as well as interface defect density on the photovoltaic performance of the solar cell was systematically explored.The results show that the larger band gap of MoSe2 helps to reduce hole recombination.At the band gap of 1.55 eV,the MoSe2/Si solar cell achieves a photovoltaic conversion efficiency of 10.19%.When the work function of the back electrode is lower than 4.6 eV,the transport of holes is severely inhibited,and the cell performance is significantly reduced.In the actual experiment,it is necessary to select a gold electrode with a large work function of 5.1 eV to form an ohmic contact with pSi to ensure cell performance.When the interface defect density is higher than 1×1012 cm-2eV-1,a large recombination current will be produced,and the cell performance will be seriously degraded.Therefore,it is of great significance to strictly control the experimental conditions and use the appropriate interface engineering to improve the interface quality.After the introduction of hydrogenated amorphous silicon(a-Si:H)with a thickness of 3 nm as the interface layer,the recombination of holes was effectively suppressed,and the photovoltaic conversion efficiency was increased to 12.31%.Besides,the effect and mechanism of several typical electron transport layer materials on cell performance improvement are discussed.