Study On The Properties Of Cu₂ZnSn（S,Se）₄ Thin-film Solar Cells Fabricated By Electrodeposition Method

Cu₂ZnSn（S,Se）₄（CZTSSe）compound semiconductor is considered as an ideal absorber material for thin-film solar cells due to its non-toxic and abundant elements,continuous tunable direct band gap（1.0～1.5 e V）and high light absorber coefficient(10⁴ cm^-1).At present,the high conversion efficiency of CZTSSe solar cells with low cost and environmental protection preparation technology is the premise to promote the large-scale application of CZTSSe solar cells.Sequential electrodeposition has a great prospect because of its advantages of non-toxic and environmental protection,simple operation,low cost and suitable for large area preparation.However,due to the different diffusion coefficient and expansion coefficient of different metals,the growth mechanism of CZTSSe absorber is complex,and it is easy to form more detrimental defects and impurity phases,which is the key factor limiting the low efficiency of CZTSSe cell prepared by layered deposition.Aiming at the issue,firstly,the preparation process was optimized to obtain Mo/Cu/Cu-Zn/Sn precursor,CZTSSe absorber and device with uniform and controllable composition.Based on the Mo/Cu/Cu-Zn/Sn stacked metallic precursor film,the growth mechanism of CZTSe was systematically studied for the first time,which provided a basis for further improving the photovoltaic performance of CZTSSe devices.Finally,the growth environment of CZTSSe was optimized by constructing the precursor film with uniform distribution of elements and phase structure.Therefore,the secondary phases and defects of CZTSe film were controlled.Based on preparation process optimization,growth mechanism study and defect control,CZTSSe thin film solar cells with 10.03%total area efficiency were prepared.The main results are as follows:1.The deposition process of metal precursor film was optimized to improve the crystallinity and uniformity of CZTSSe film.The roughness of Sn metal layer is a major issue for the preparation of CZTSSe by the sequential electrodeposition.Adding RX-851 additive to Sn precursor solution can slow down the reduction rate of Sn²⁺and effectively improve the roughness of Sn metal layer,providing good conditions for element uniformity of absorber.In addition,by adjusting the deposition charge of Zn,Zn Se secondary phase and holes in the back interface of CZTSSe film were eliminated.The CZTSSe film was successfully prepared without secondary phase and with good crystallization.By changing the electrodeposition orientation of the sample,the enrichment of Cu elements at the bottom of the film and the formation of Cu_2-xSe phase were eliminated.The uniform absorber and CZTSSe solar cells were successfully prepared,and the efficiency was6.60%.2.Based on Mo/Cu/Cu-Zn/Sn stacked metallic precursor film,the growth mechanism of CZTSSe was systematically studied for the first time,which provides a theoretical foundation for improving the performance of CZTSSe cells.The phase structure,microstructure and element distribution of the thin films selenized at 280～580℃were systematically studied.The binary and ternary selenides(Sn Se,Cu_2-xSe,Zn Se and CTSe)were firstly generated from the metallic laminated precursors（280℃）,and the element distribution was chaotic.With the increase of temperature（320～400℃）,these selenides gradually synthesize CZTSe with uniform element distribution but small grain size.Increasing the temperature（450～540℃）,the small grains of CZTSe gradually grow up to form smooth and compact CZTSe films.When the temperature is higher than 540℃,CZTSe is decomposed.The crystallinity of CZTSe becomes poor and Zn Se is formed.Therefore,540℃is the best growth temperature of CZTSSe.Based on this absorber,CZTSe thin film solar cell was prepared with an efficiency of 7.27%.3.The effects of two precursors with different element distribution and phase structure on CZTSe secondary phases and defects were discussed.The quaternary selenide precursor film can effectively inhibit the formation of Zn Se phases and Cu _Sn defects,improve the concentration of V_Cu defects,and enhance the photovoltaic performance of CZTSSe devices.Two kinds of precursors were designed:binary-ternary selenide precursor and quaternary selenide precursor.CZTSe absorber prepared from binary-ternary selenide precursor film has more secondary phases and detrimental intrinsic defects.Quaternary selenide precursor film has a pure phase structure and uniform element distribution,which provides a good environment for CZTSe growth.The obtained absorber has higher carrier concentration and fewer detrimental intrinsic defects,thus significantly improving the photovoltaic performance of CZTSe solar cells.Based on the precursor of quaternary selenide,Sn S and Mg F₂ antireflection layer were introduced into the selenization process to obtain CZTSSe cells with an efficiency of 10.03%（the active area efficiency is 10.90%）,which is the best conversion efficiency of CZTSSe thin film solar cells prepared by electrochemical deposition at present.