| Cu2ZnSn(S,Se)4(CZTSSe)with zinc chalcopyrite structure is expected to become a photovoltaic material with high performance and high commercial application value due to its rich‘constituent elements'and environmentally friendly,and high preparation efficiency by solution method.It is also one of the best materials for‘thin film photovoltaic architectural integration'.Vacuum method and non-vacuum method are commonly used to prepare high-quality absorption layer.The solution method of non-vacuum method does not require vacuum environment,has low cost and is simple and easy to operate,which is widely used in the preparation of CZTSSe.In a short period of twenty years,the CZTSSe efficiency has increased to 12.6%,but there is still a big gap compared with the highest theoretical efficiency(32%).It was found that the three factors affecting the photoelectric conversion performance of CZTSSe battery were the properties of the absorption layer material itself,the crystal quality of the absorption layer and the structure of the battery.Because the absorption layer is the core of solar cells,its quality directly determines the efficiency of the battery,so it is of great significance to explore the preparation process of high quality CZTSSe.In this paper,DMSO and DMF were used as solvents to study the preparation process of CZTSSe absorption layer film,and the influence of I-on the film-forming process and the performance of battery devices was explored.The following results were obtained:(1)With Cu(CH3COO)2,ZnCl2,SnCl2 and thiourea as precursor solution solutes and DMSO as solvent,the influence of selenization conditions on the film was investigated.The film with good crystallinity and compactness was obtained at 550°C for 15 min.The device was assembled to obtain 7.6%photoelectric conversion efficiency,and the carrier behavior of its film,deposited Cd S and assembled device was further studied.It was found that compared with perovskite solar cells,its carrier life was shorter.Then the precursor solution solute was changed,and it was found that the addition of iodide had a great influence on the morphology of the film.When only Znsource was replaced by ZnI2,high quality thin films with less secondary phase were obtained by optimizing the precursor preparation conditions,and thin films with smooth and dense surface and large grains throughout the absorption layer were obtained by two-step selenization method.We also replaced DMSO with DMF solvent with higher solubility,and the prepared film showed stratification.(2)This paper used different proportions of ZnCl2 and ZnI2 as precursor solution to explore the effect of I-on CZTSSe films and solar cells.With DMSO and DMF as solvents,0-100%ZnI2 was prepared to replace ZnCl2,and a series of phase characterization methods such as XRD,Raman,SEM and EDS were used to explore the effect of I-content on the phase of CZTSSe film.When DMF was used as solvent,the highest efficiency without I-was8.9%,and the highest efficiency with I-was 7.9%.When DMSO was used as solvent,the highest efficiency of no I-was 7.2%,and the highest efficiency of I-was 8.98%.We found that the morphology changed greatly when the concentration of I-was high,but the morphology changed little when the concentration of I-was low.The main innovations of this paper are as follows:(1)Iodide was used as the precursor solution to prepare a smooth and dense film,which has the potential of high-efficiency solar cells.The highest efficiency of I-was 8.98%;(2)Transient surface photovoltage(TSPV)technology was used for the first time to investigate the separation,transmission and recombination of photogenerated carriers in the device.It is found that,compared with perovskite solar cells,CZTSSe solar cell device has ultra-high photovoltage,and the separation time of photogenerated carriers is very short.The recombination time is positively correlated with the photoelectric conversion efficiency,and the higher the open circuit voltage is,the longer the carrier lifetime is. |
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