Preparation Of Cu₂ZnSnS₄ Thin Films With Element Gradient Distribution

In recent years,Cu?In,Ga?Se₂?CIGS?solar cell components have developed steadily,with the maximum efficiency of 22.3%,but the scarcity of raw materials?In and Ga?leads to its high cost,which has become the biggest obstacle to its continued development.Compared with CIGS thin film solar cell,Cu₂ZnSnS₄?CZTS?thin film cell has the outstanding advantages of rich raw materials and excellent photovoltaic performance?the theoretical photoelectric conversion efficiency is 32.2%?,and the two kinds of batteries have similar cell structure.Therefore,CZTS thin film solar cell becomes the preferred substitute for CIGS thin film solar cell,which has received general concern f'rom scholars at home and abroad.Although the efficiency of CZTS theory is very high,the actual efficiency is still low.The main reason is that its short circuit curreint?Jsc?and open circuit voltage level?Voc?are relatively low.At present,the absorption layer with the gradient of In and Ga elements is widely used in the CIGS thin film solar cell.The gradient distribution of metal elements will promote the formation of the gradient band gap in the absorption layer.This structure can reduce the rate of carrier recombination in the absorption layer and at the interface,and thus effectively improve the Jsc and voc of the cells.As the preferred alternative material for CIGS,the construction of gradient structure can also be used as an effective means to optimize the performance of CZTS cells,but the related reports of CZTS thin film solar cells with element gradient are still very scarce.It has been shown that the change of metal element content in CZTS can affect the band gap of the material,for example,with the increase of Cu content,the band gap of CZTS gradually decreases,and with the increase of Sn content,the band gap of CZTS increases gradually;in the rich Zn region,with the increase of Zn content,the band gap of CZTS gradually decreases.The above results provide a theoretical basis for the preparation of gradient band gap CZTS thin films.In view of this,the purpose of this study is to use co-sputtering technology to realize the gradient distribution of metal elements in the film by controlling the sputtering power of the target,and to prepare the CZTS film with the metal element gradient,and to clarify the influence law and mechanism of the preparation process on the distribution of thin film elements,which provides the theoretical basis and experimental support for the gradient structure of CZTS film band gap.In addition,this paper attempts to prepare CZTS thin film solar cells by full magnetron sputtering technology,and explore a more convenient preparation method of CZTS thin film solar cells.The results show that the gradient distribution of metal elements in CZTS films can be achieved by controlling the gradient change of the target power in the co-sputtering process,and the CZTS thin film cells with good microstructure and phase composition have been prepared by totally magnetic sputtering.The main conclusions are as follows:?1?when the metal elements in the CZTS thin film form a gradient distribution,the thin film will produce component segregation,but by controlling the gradient sputtering process,the CZTS films with pure phase and good microstructure can still be obtained;?2?with the increase of the sputtering power gradient of ZnS,SnS₂ and Cu₂S targets,the distribution gradient of metal elements in the film is enhanced;if the Zn element gradient is formed in the deposited film,the gradient distribution of the Zn element can still be maintained after annealing,but if the Cu element gradient is formed in the deposited film,the gradient of the Cu element is difficult to maintain after the annealing.?3?The band gap gradient structure in the thin film can be realized by changing the gradient distribution of the Zn element,and the band gap size and form can be simulated approximately.The band gap gradient structure in the thin film can be realized by changing the gradient distribution of the Sn element,but it can only describe its form from the theoretical point of view,and the size of the band gap can not be calculated by simulation.Because the gradient distribution of Cu element is not very ideal,the gradient structure of band gap structure is more difficult,so it can hardly be built and simulated.?4?in the preparation of the CZTS thin film solar cell,the CZTS thin film battery with good microstructure and controllable structure can be prepared by magnetron sputtering in all films.The efficiency of the cell is 3.95%,but the interface between the top electrode Al and the window layer AZO still needs to be improved.