Studies On The Regulation Of CZTSSe Precuror Solutions And High Efficiency Photovoltaic Devices

Nowadays,as the first generation solar cell is constantly approaching the theoreticallimit,thin film solar cells provide greater development space and broader application prospects for the photovoltaic field.As a new type of thin film photovoltaic absorber material,Cu₂Zn Sn?S,Se?₄?CZTSSe?is a non-toxic,stable and direct band gap semiconductor material with proper band gap,which can be prepared by the solution method.The mixed solvents based on thiols and amines show a very strong dissolving ability to metals and their compounds,so they are widely used in the field of CZTSSe.The disadvantage is that the decomposition products of organic reagents are easily left in the precursor film and directly affect the CZTSSe crystal growth process.The most intuitive and general performance is that a carbon-enriched fine grain layer will be formed under the CZTSSe polycrystalline layer with photoelectric conversion function and it is hardly to be removed by adjusting the selenizing process parameters.In order to obtain a pure precursor film,improve the photoelectric conversion efficiency of CZTSSe solar cell and promote the development of solution method,this paper mainly carries out research work from two aspects as follows.Firstly,in terms of solvent engineering,the water-soluble thioglycolic acid?TGA? was used as the core reagent for dissolving metal oxides,and ammonia was used instead of amines to prepare the aqueous precursor solution,thereby reducing the carbon content at the source.On this basis,the effects of the molar ratio of ammonia and TGA on the dissolution process of metal oxides and the coordination state of metal ions in solution were systematically studied by nuclear magnetic resonance and Raman spectroscopy.The results show that both the carboxyl and mercapto group of TGA can coordinate with metal ions,and there is a competitive relationship with each other.The coordination types between TGA and metal ions can be changed by adjusting the deprotonation degree of TGA with ammonia,and then change the types of coordination groups of metal ions.In the solution with high molar ratio of NH₃ to TGA,the metal ions mainly coordinate with mercapto group,and the carboxyl group was released into the water environment to improve the solution stability.Finally,by using a precursor solution in which the molar ratio of NH₃ to TGA is equal to 2.0,a device with a certificated photoelectric conversion efficiency of 12.0%was prepared.This is currently the highest efficiency of CZTSSe thin film solar cells prepared by water-based solution systems.Secondly,in terms of preparing high-quality films,on the basis of integrating the optimization results of the solvent system,the precursor film was further air annealed,and the effects of annealing temperature and time were systematically studied.The results show that the precursor film could be violently oxidized and destroyed when the temperature reaches 550?;when the temperature didn't exceed 350?,the fine grain layer in the selenized film couldn't be completely eliminated,even if extended the air annealing time.However,when the temperature reaches 450?,the proportion of the large grain layer in the selenized film increased significantly with the increase of annealing time,and the small grain layer was completely eliminated in the sample annealed for 20 min.After analyzing the air annealed precursor film by EDX and XPS techniques,it was found that the content and valence of metal elements were not affected,while the content of carbon elements was significantly reduced,indicating that air annealing is an effective method to remove carbon residues.Based on this method,an absorber layer composed of a single large grain layer was prepared and assembled into CZTSSe thin-film solar cell.Compared with the untreated sample,the device efficiency increased by nearly 40%.