| As a typical material for the transition metal sulfur compounds,two-dimensional MoS2has strong optical absorption(5×105 cm-1)and high carrier migration(100 cm2·V-1·S-1),the band gap width varies from single layer 1.9 eV to body material 1.3 eV with thickness,also has great potential in the new electronic,photoelectric and photovoltaic devices.Si solar cell is dominant in the PV market because of its rich materials and mature technology.Combined with the above two advantages,the preparation of new MoS2/Si heterojunction solar cells has become a hot research direction of low cost solar cells.In this paper,the preparation of MoS2 thin films and the structure design of high efficiency MoS2/Si heterojunction batteries are studied.First,the crystalline MoS2 thin films were prepared by chemical vapor deposition?CVD?.The morphology evolution mechanism of MoS2's triangle nucleation and growth process from triangle to sharpening triangle was studied.Amorphous-microcrystalline MoS2 films were prepared by sol-gel method.The adjustment mechanism of the microstructure of MoS2 films and the transition of amorphous to microcrystalline phase transition by H2 flow and annealing temperature were studied.Secondly,the ITO/MoS2/p-Si/Ag heterojunction solar cell was prepared,which proved that the MoS2 layer had chemical passivation to reduce the compound of the battery interface,and also had the field passivation effect on the width of the depletion layer of the battery.In order to improve the performance of the battery,the p+layer was inserted at the back of the ITO/MoS2/p-Si/Ag battery.It was proved that the high and low junction between the p+and P layers and the ohm contact between the p+layer and the Ag electrode could effectively eliminate the S-characteristics of the J-V characteristics of the battery.Meanwhile,the p+layer insertion could effectively reduce the battery series and Ohm shunt loss.Thirdly,the photoelectric conversion characteristics of ITO/MoS2/p-Si/p+-Si/Ag battery devices with different MoS2 microstructure were studied,and the physical mechanism of improving the photovoltaic performance by controlling the microstructure of MoS2 was revealed.Finally,the MoS2-xOx thin film was deposited by the double source co-evaporation method,and the ITO/MoS2-xOx/n-Si/n+-Si/Ag structural battery devices with different oxygen content x were prepared.The photoelectric conversion and carrier transmission characteristics of the batteries revealed that the proper adjustment of X could improve the work function of the MoS2-xOx,thus the band bending at the MoS2-xOx/Si interface was formed.Impeding electron transport effectively enhances the hole selection selectivity of MoS2-xOx.By introducing MoOx passivation layer on the MoS2-xOx/n-Si interface,the maximum conversion efficiency of the battery reaches 15.8%.The specific research contents are as follows:1.MoS2 thin slices with different shapes were synthesized on SiO2/Si substrate by CVD method.The nucleation mechanism and morphology evolution were analyzed.The results showed that the initial nucleation was triangular.A high quality monolayer MoS2 film was obtained by controlling the nucleation density,grain size and shape.2.The amorphous-microcrystalline MoS2 films were prepared by sol-gel method.The regulation of H2 flow and annealing temperature on the transformation of amorphous to microcrystalline phase transformation and the adjustment mechanism of microstructure of MoS2 films were studied.When the flow rate of H2 is low,the film is basically amorphous,and the increase of H2 flow makes the film occur from amorphous to microcrystalline phase transition.The mechanism can be attributed to the enhancement of the etching of the amorphous weak bond by hydrogen.The films prepared at 0sccm have the highest XRD?002?peak strength and the highest proportion of Mo 6+,indicating that the hydrogen etching and the sulfur removal reoxidation reaction reached equilibrium,H2 flow rate.Again,the strong hydrogen etching leads to the increase of film defects,the decrease of XRD?002?peak intensity and the decrease of Mo 6+ratio.The increase of annealing temperature mainly results in the enhancement of reoxidation reaction,and also the transformation process of amorphous structure to microcrystalline phase.3.The ITO/MoS2/p-Si/Ag structure heterojunction battery was prepared.The effect of MoS2 film insertion on the photovoltaic performance of the battery was studied.The results revealed that the chemical passivation of the MoS2 thin film reduced the defect of the ITO/p-Si interface and increased the open circuit voltage of the battery.In order to optimize battery performance,P+layer was introduced into the back interface of ITO/MoS2/p-Si/Ag battery,and the mechanism of S-type J-V characteristics was studied.The results revealed that the high and low junction between the P and p+layers and the Ohm contact between the p+layer and the Ag electrode caused the S-type of J-V characteristics to disappear.4.The effects of MoS2 films with different microstructure and valence state on the performance of ITO/MoS2/p-Si/p+-Si/Ag cell devices are studied.The physical mechanism that restricts the efficiency of the battery is studied through the analysis of the relationship between the film structure and the photoelectric conversion characteristics.J-V and the quantum efficiency analysis revealed that with the increase of H2 flow,the short-circuit current,open circuit voltage and conversion efficiency of the battery increased first and then decreased.When the H2 flow rate was 70 sccm,the performance of the heterojunction battery was the best and the conversion efficiency reached 7.55%.The improvement of short circuit current is attributed to the dense structure and fewer interface defects in the phase transition region,and the defect recombination at the grain boundary is reduced.The increase of open circuit voltage is attributed to the increase of Mo 6+ratio in the films.The optimized band structure increases the built-in potential of the battery.In addition,the thin film makes the battery have small serial ohmic loss and ohmic shunt,and the FF factor has been significantly improved.5.The MoS2-xOx thin film is deposited by the double source co-evaporation method.The ITO/MoS2-xOx/n-Si/n+-Si/Ag structure battery devices with different oxygen content x are prepared.The microstructure and optical absorption characteristics show that the Mo 4+in the MoS2-xOx film is substantially constant first and then gradually decreases with the increase of the content of oxygen.The optical band gap and the order of the films increase first and then decrease.The optical band gap of the films reaches 3.5eV and has the highest microcosmic ordering.The Voc of the battery showed an increasing trend with the oxygen increasing,while Jsc increased first and then decreased.The increase of Vocc is attributed to the fact that oxygen incorporation hindered the destruction of MoS2-xOx/n-Si interface passivation by sulfur and resulted in the decrease of carrier recombination at the interface.The relative optimization of the short-circuit current is attributed to the adjustment of the film's work function and the increase of film order by an appropriate oxygen incorporation.By introducing MoOx passivation layer at the MoS2-xOx/n-Si interface,the short circuit current and open circuit voltage of the battery are improved simultaneously.The Voc,FF factor and Jsc of the battery are 623.8 mV,73.08%,35.56 mA·cm-2,and the conversion efficiency is 15.8%. |
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