Preparation And Photovoltaic Properties Of CZTSSe Thin Films And Solar Cells

Flexible thin film solar cells have some unique advantages like low-mass,high power density to mass ratio,bendable property and suitable for roll to roll production,bringing about wide application areas such as space electrical source,BIPV and so on.Cu₂ZnSn?S,Se?₄?CZTSSe?thin film,as an alternative to Cu?In,Ga?Se₂?CIGS?,is much cheaper due to the absense of noble metal elements In.CZTSSe has a tunable band gap from 1.0 eV to 1.5 eV with a high light absorption coefficient of over10⁴ cm^-1,which makes it a suitable solar cell absorber layer material,thus has obtained more and more attention in recent years.In this thesis,CZTSSe thin films were obtained by selenizing sputtered precursor.At first,the process of preparing CZTSSe thin film on rigid substrate was studied.It is found that a three-layer structure precursor was able to control the composition of the film and improve the crystallization of CZTSSe.The top and bottom layers of the precursor were prepared by co-sputtering Zn and CZTS targets,while the middle layer was deposited by co-sputtering Cu and CZTS targets.A low Zn sputtering power leads to a Cu-poor and Zn-poor composition in CZTSSe thin film and a high Zn sputtering power will form extra ZnS phase,which harms the performance of the solar cell.When the Zn sputtering power was 14W,the conversion efficiency of CZTSSe solar cell reached its maximum of 3.86%.Then flexible CZTSSe solar cells were prepared using Ti foil as substrate.The effects of different barrier layers on flexible CZTSSe thin films and solar cells were studied.Cr,ZnO and TiN barrier layers all perform their capability in suppressing element diffusion from the substrate to CZTSSe thin films,leading to less TiSe phase forming and high crystallization of thin film.Among them,TiN had the best suppression effect.The efficiency of flexible CZTSSe solar cell based on TiN barrier layer was 1.85%,which was 67%more than that with no barrier layer.Finally,A simple K doping process was developed in preparation process.The effects of K doping on performance of CZTSSe thin film and flexible solar cells were studied.It is found that the K doping can promote the growth of grains,improve films'crystallization and enlarge the band gap of CZTSSe thin film.In addition,K doping can adjust the conduction band match at the interface of CZTSSe and CdS.With small amount of K doping,slight change of conduction band offset?CBO?was observed.When it comes to large amount of K doping,secondary phases were formed in the film,which harms the fully growth of grains and the interface CBO match.When K doping amount was 1.0?mol,a CZTSSe thin film with grain size of over 1?m,strong?112?preference orientation and optimal CBO match was obtained.The flexible solar cell based on that reached the efficiency of 3.06%.