Preparation Of Solar Cell Cu₂ZnSnS₄ Absorbing Layer And ZnS Buffer Layer By Direct Solution Method And Their Properties

With the progress of science and technology,the demand for emergy is improved rapidly.The drawbacks of traditional fossil fuels are increasing day by day which greatly promoted people's exploration in the field of new energy.In recent years,the most noteworthy one is the thin film solar cells,which still have good stability and considerable photoelectric conversion efficiency in harsh conditions.Although the CIGS thin-film solar cells have made considerable progress,their development is still limited due to the limitation of the material itself.So the researchers are looking for alternative elements actively.The CZTS thin film solar cells have attracted wide attention of scholars recently.The advantage of CZTS is that its constituent elements are abundant on earth,non-toxic,environmentally friendly and inexpensive to prepare.CZTS has the same lattice structure as CIGS,which will preserve the excellent properties of CIGS perfectly.In this paper,we propose a green,non-polluting and low-cost direct solution method to prepare the Cu₂ZnSnS₄ absorber layer and the ZnS buffer layer of the thin film solar cell.We explored the precursor ink-related properties,and researched the impact of heat treatment and curing processes on film performance.Finally,we can prepare the Cu₂ZnSnS₄ thin film and ZnS buffer thin film with excellent performance.Specific content and conclusion are as follows:(1)Prepare Cu-TU,Zn-TU,Sn-TU binary particle-free ink at first.The three inks were mixed together to obtain a particle-free Cu₂ZnSnS₄ precursor ink.The thermal decomposition of precursor ink was investigated by TG-DSC-MS.The most suitable precursor ink ratio is 2:1:1:8.By changing the amount of solute added,different concentrations of inks were prepared from a low concentration of 0.3 M to a high concentration of 1 M.(2)The ink film pretreatment process and subsequent vulcanization process were investigated detailedly.The optimal Cu₂ZnSnS₄ film preparation process was as follows:Pretreating the film at 250? for 30 min,followed by curing the film at 560?for 10 min.It is shown that the CZTS film is compact and uniform and fine grows into large columnar grains with a size of 1.5 ?m.The carrier concentration is 1017?1018 cm-3 and the film is a p-type semiconductor.(3)Another important factor for CZTS solar cells is buffer layer.ZnS film prepared by direct solution method can meet the performance requirements of buffer layer.The suitable solvents and complexing agents were selected to prepare precursor inks with different molar ratios.TG-DSC-MS analysis was conducted to grasp the thermal decomposition information from room temperature to 500?.The XRD analysis shows that the ZnS thin film was of good crystallinity and has preferred orientation of(002)plane.When the heat treatment process is 200? and 250? for a holding time of less than 30 min,the film is dense and smooth.The band gap of ZnS thin film is about 3.3 eV.ZnS prepared by direct solution method can meet the performance requirements of buffer layer.