Preparation Of CZTSSe Thin Films By Low Toxic Solution Method And Effects Of Rare Earth Doping On CZTSSe Thin Films Properties

CZTSSe thin film solar cell has become the best candidate for the solar cell absorption layer materials and one of the most developing prospects of thin-film solar cells in the future,which is contributed to the many advantages of CZTSSe absorption layer,for example,raw materials of CZTSSe films are rich and low toxic,the preparation of CZTSSe thin films is simply easy to operate,its band gap is adjustable,its absorbance coefficient is more than 10⁴ cm^-11 and the theoretical value of photoelectric conversion efficiency is high and so on.1.The CZTSSe films were prepared by the low toxic solution method.Based on data analysis of the phase structures,the morphology,elements content,element valence states,element distributions and photoelectric performances,we explored the influences of the annealing process conditions,including low temperature annealing temperature,selenized annealing temperature and time,on the properties of CZTSSe films.The results showed that the optimum process conditions are given,that is,the heat treatment temperature of spin coated film was 320℃,selenized annealing temperature was 540℃,and selenized annealing time was 10 min.Under the prepared conditions of the CZTSSe film showed good performances,namely the CZTSSe with copper poor and zinc rich ingredients（Zn/Sn=1.06,Cu/（Zn+Sn）=0.82,it was closed to the optimal ratio）,good grain morphology,no holes,Mo（S,Se）₂layer’s thickness of about 100 nm,optical band gap of 1.16 eV;The photoelectric conversion efficiency of CZTSSe thin film solar cell was 1.65%.2.CZTSSe thin films with different concentration gradients doped with cerium and lanthanum（Ce/（Cu+Zn+Sn）=0,1,3,5,7%;La/（Cu+Zn+Sn）=0,1,3,5,7,10%）were prepared by low-toxicity solution method.Experimental investigations found that the doping of rare-earth cerium and lanthanum could promote the grain growth of the films.According to phase analysis,rare-earth elements may not enter the CZTSSe lattices.When the doping ratio of Ce/（Cu+Zn+Sn）=5%,Zn/（Sn+Ce）was 1.06,Cu/（Zn+Sn+Ce）was 0.88;when the doping ratio of La/（Cu+Zn+Sn）=7%,Zn/（Sn+La）was 1.03,Cu/（Zn+Sn+La）was 0.81.The proportions of elements were closed to the optimal value of copper poor and zinc rich,elements valence states were in accordance with the reported valences,and rare earth element lanthanum,cerium had shown+3 valence.And the doped with rare earth elements could adjust the optical band gap values and improve the electrical properties of thin films.According to the analysis of the phase structures,the morphology,elements content,element valence states,element distributions and photoelectric performances,the optimal doping ratios of rare earth cerium ions were obtained respectively,namely,Ce/（Cu+Zn+Sn）was 5%,La/（Cu+Zn+Sn）was 7%.