Preparation And Improvement Of CZTSSe Thin Film Solar Cells By Element Solution Method

Semiconductor Cu₂ZnSn?S,Se?₄?CZTSSe?has received considerable interest,due to their highabsorption coefficient,high stability,suitable band gap and low material cost.Recently,CZTSSe thin film solar cells have achieved high efficiency of 12.6%.Various approaches have been developed to fabricate the absorber layers,including vacuum method and nonvacuum method.The vacuum methods include thermal evaporation and magnetron sputtering method.And the nonvacuum methods include molecule precursor solution method,nanoparticle solution method and electrodeposition method.Compared with the complex and expensive vacuum method,molecule precursor solution method has the advantage of low expense and simple operation,which is favored by industry.At present,Mitzi's group used the hydrazine as solvent to dissolve metal sulfide and metal selenide followed by preparing the CZTSSe thin film solar cell.And they achieved 12.6%high efficiency.But hydrazine is a inflammable and explosive solvent,it will be disadvantage for industry and laboratory.So,we should use a green and safety solvent to prepare CZTSSe thin film.At present,some groups use the green and safety solvent to dissolve the metal chloride ormetallic oxide,which will introduce the Cl or O heteroatom and decrease the efficiency of the the solar cell.The desired materials are the metal element,metal sulfide and metal selenide.But the reported solvent can not dissolve these materials except hydrazine.However,we use the 1,2-ethylenediamine and1,2-ethanedithiol can solve the problem.It can not only dissolve the metal sulfide and metal selenide,but also can dissolve the metal element.To solve the impurity atom problem,we prepare CZTSSe thin film,using 1,2-ethylenediamine and 1,2-ethanedithiol as solvent to dissolve metal element.This article has three parts:1.The preparation of CZTSSe thin film solar cell:we explored the solubility property of 1,2-ethylenediamine and 1,2-ethanedithiol.We successfully dissolved the metal element of Cu,Zn,Sn,Se and fabricated CZTSSe precursor thin film by spin-coating method and preheating process.Through studying the environment of preparing thin film,selenization condition and thickness of the thin film,we successfully got CZTSSe thin films with well-crystallized.We use the selenized CZTSSe thin films to assemble devices,achieving an efficiency of 3.26%.2.The improvement of open-circuit voltage(V_OC)and fill factor?FF?of CZTSSe thin film solar cell:Due to the excessive Se powder dissolved in the solution,the thin film has the low band gap and is loose.The low band gap will cause the low V_OC.And the loose and porous structure will hinder the carrier transfer and increase series resistance?R_s?,which will decrease the FF.So,we use the S powder instead of some Se powder in the solution,which will increase the band gap of the film and decrease the holes in the film.Finally,we achieved the highest efficiency of 6.57%with the S content of 90%.3.The decrease of secondary phase in the CZTSSe thin film:To prepare the CZTSSe thin film, we need to selenized in the high tempreture,which will cause the Sn element loss seriously.And the loss of Sn will cause the the increase of Cu and Zn element,relatively.Generally,high content of Cu and Zn element will easily cause the formation of CuSe and ZnSe secondary phase.Through the XRD and Raman analyzation of CZTSSe thin film,we found that some secondary phases?CuSe,ZnSe?have existed in the thin film.Through the analyzation of EDX,we found these secondary phases were caused by the loss of Sn.To solve this problem,we add excess Sn in the solution to compensate the Sn loss.Through the XRD and Raman analyzation of CZTSSe thin film,we find that the secondary phase of CuSe and ZnSe were successfully decreased and disappeared with the increase of Sn.But,when we add overmuch Sn,it will form a new secondary phase?SnSe₂?.Finally,we achieved the highest efficiency of 8.71%with an additional Sn content of 15%.