Study On Cu₂ZnSnS₄ Thin Films And CZTS Thin Film Solar Cells Via Sol-gel Route

As one of the most promising absorber candidates in thin film solar cells,copper Zinc Tin Sulfur(Cu2ZnSnS4,CZTS)is paid much attention due to its innocuity,high efficiency and low cost.CZTS has kesterte structure generally with a direct band gap of 1.45 eV which is close to the optimum band gap(1.5 eV)of absorber layer and its absorption coefficient is larger than 104 cm-1.In addition,its power conversion efficiency reaches 32.2%in theory.Therefore,CZTS is suitable for the absorber layer in solar cells.In this dissertation,CZTS thin films were fabricated by sol-gel and sulfurization method.The effects of preheating treatment on the CZTS prcursors and the sulfurization process on the structural,morphological and photoelectrical properties of the CZTS thin films were investigated.Meanwhile,the CZTS thin film solar cells(CZTS TFSCs)were developed and the solar cell parameters which would effect on the CZTS TFSCs properties were investigated.The main results are as follows:1.The mechanism of the sol-gel reaction process was investigated.The forming process of the molecular model of metal-thiourea-oxygen complexes and the mechanism of thermal decomposition reaction process of preheating treatment process of CZTS prcursors were elucidated.On this basis,the optimization fabricating parameters of the CZTS precursors were obtained.The excellent performance CZTS precursors were fabricated.2,Research revealed the technological conditions on the properties of the CZTS thin films and the solar cells.And the optimization technological parameters of the CZTS thin films were gained:the sulfurization temperature was 500 ?;sulfurization time was 90 min;H2S concentration was 5%;Cu/(Zn+Sn)=0.87 and Zn/Sn=1.15.The excellent parameters of the CZTS thin films were as follows:Eg=1.47 eV,p=1.25 ?·cm,?=2.41 cm2/(V·s),p=3.31×1018 cm-3.Otherwise,the effects of thicknesses of buffer layers CdS thin films and different window layers(AZO and ITO thin films)were investigated.The research results show that the conversion efficiency was 1.58%when the buffer layers were 50 nm CdS thin films;the conversion efficiency was 1.58%when the window layer were 200 nm AZO thin films;the conversion efficiency was 1.52%when the window layers were 450 nm ITO thin films.3.The effects of thicknesses of Cd-free buffer layers ZnS thin films were investigated.The research results show that the conversion efficiency was 1.45%when the buffer layers were 50 nm ZnS thin films.