Study On The Preparation, Etching And Performance Of Thin-film Solar Cells Of Copper-zinc-tin-sulfur Films

The Cu₂ZnSnS₄（CZTS）materials has been widely researched as a hot spot in recent year,it has a suitable optical band gap of 1.45e V,which is close to the theoretically optimal value,and has an absorption coefficient of up to 10⁴/cm^-1,which is very suitable as the absorb layer in thin film solar cell.The pulsed laser deposition（PLD）technique is a suitable thin film deposition method for preparing CZTS thin film.However,when the CZTS thin films are fabricated by PLD method,the samples have the problem that the surface morphology is too rough,resulting in more defects and affect the property of the thin film.On the other hand,CZTS thin films may have harmful secondary phases at the Cu-poor and Zn-rich ratio,which due to the narrow stable phase region.Aim to solve those problems,this paper mainly discuss the preparation of CZTS thin film using shadow masked pulsed laser deposition（SMPLD）to avoid the roughness problem caused by PLD method.Then we researched the influence of etch method used in the sample of the CZTS thin film,and finally the CZTS thin film solar cell devices were fabricated.The details are as follows:In the first part,the preparation parameters of CZTS thin film prepared by SMPLD method were studied,and then we fabricated the CZTS thin film by the SMPLD method through the parameters.The samples prepared by SMPLD will contrasted with the samples fabricated by common PLD method through the performance characterization.It was found that the samples prepared by SMPLD method were more compact and uniform.The surface roughness decreased an order of magnitude while the crystal properties degree is roughly equivalent.In the second part,we analyzed the possible second phase in the CZTS thin film and listed the influence of these second phases on the CZTS thin film and solar cell.But the second phase in CZTS thin films prepared by different deposition methods is different due to the different elemental ratios.Based on ultraviolet Raman spectroscopy（excitation light with 325nm）,X-ray diffraction spectrum and other characterization methods,we confirmed that the second phase mainly in the CZTS thin film sample that we prepared by the PLD method was ZnS.And then we used the hydrochloric acid（HCl）as a selective chemical reagent to remove the ZnS secondary phases,and the difference in characteristics of the samples before and after the etching treatment was studied.In the performance characterization of the samples after etching,we found that the ZnS secondary phase has significantly decreased through soaking the samples in the hydrochloric acid.In the last part,we analyzed the performance requirements of each layer in preparation of solar cells,and prepared each layers using a suitable parameters,including:back electrode layer,buffer layer,window layer and Top electrode.Focus on the methods’effectiveness,the CZTS solar cell devices have been prepared by the different methods mentioned in the previous two parts,then the samples will characterized and compared with the samples which fabricated by common PLD method...Finally,by comparing the performance characterization of the samples of the solar cell devices,we confirm that the two methods mentioned in previous two parts are effectively in fabricating CZTS solar cell devices.The device was fabricated several times to verify its repeatability,and a 4.3%efficiency CZTS thin film solar cell was finally obtained.