Cu₂M_xZn_1-xSnS₄(M=Ni,Co) Nanocrystalline And Its Thin Film The Phase Can Be Controlled For Preparation And Physical Property Research

Cu₂ZnSnS₄-based is a p-type semiconductor material with a similar crystal structure to Cu（In,Ga）Se₂ and has a series of excellent properties.For example,the element is non-toxic and abundant in the earth’s crust,the band gap of CZTS is close to the optimal band gap 1.45 eV of single-junction thin film solar cell,and the absorption coefficient can reach 10⁴-10⁵ cm^-1.It can overcome the limitation of rare material in traditional Cu（In,Ga）Se₂ and CdTe solar cell.Compared with traditional solar cell absorber layer material,it has the advantage of being safe and low cost.It has become a potential alternative to the traditional absorbers for thin film solar cell.CZTS-based materials are composed of many elements,the complex composition means that the composition and its uniformity are more difficult to control,and it faces the problems of secondary phase generation and low defect tolerance.Therefore,the requirement of the element ratio is relatively high,and the existence of some defects of its own causes the large open circuit voltage deficit in CZTS to limit the efficiency of CZTS-based thin film solar cell.In order to improve the efficiency of solar cell,this paper adopts transition metal ion（Ni,Co）replaced the Zn in the CZTS materia.The substitution of the transition metal ion can reduce the formation of the second phase,suppress the generation of anti-occupation defects,and improve the carrier lifetime.The photoelectric properties of the CZTS-based material are ultimately improved.Oleylamine（OLA）is used as solvent,Cu₂M_xZn_1-x-x SnS₄（M=Ni,Co,x=0,0.1,0.3,0.5,0.7,0.9,1）was prepared by replacing the Zn element in CZTS with different content of Ni and Co by heat-up method under open-air condition.It is found that with the increase of the substitution amount of transition metal Ni and Co,the XRD and Raman spectra of Cu₂M_xZn_1-xSnS₄ samples can be seen to change from metastable wurtzite Cu₂ZnSnS₄（x=0）to kesterite Cu₂M_0.7Zn_0.3SnS₄（x=0.7）,finally converted to stable stannite Cu₂NiSnS₄/Cu₂CoSnS₄.The UV-Vis absorption spectroscopy showed that the ion-substituted Cu2MxZn1-xSnS4（x≠0）nanoparticles have more significant light absorption properties in the visible and near-infrared regions than the pure phase wurtzite CZTS materials.By changing the substitution amount x of the transition metal element,band gap of Cu₂Ni_xZn_1-xSnS₄ and Cu₂Co_xZn_1-xSnS₄ nanocrystals was nearly linearly adjusted from 1.53 eV to 1.30 eV and 1.27 eV with the increase of substitution amount,respectively.It matches the optimal band gap of the solar cell.The CZTS,CNZTS（x=0.5）,CNTS,CCZTS（x=0.5）and CCTS thin film were prepared by spin-coating the blended ink on si substract.The effect of cation substitution on the properties of the film was explored.After the vulcanization annealing,the CZTS film is still consistent with its powder structure.CZTS,CNZTS（x=0.5）and CNTS film still have good absorption capacity for sunlight in the visible and near-infrared regions.Although the absorption capacity of CCZTS（x=0.5）and CCTS films in the near-infrared region and the visible region is slightly lower than that of CNZTS（x=0.5）and CNTS,it is still suitable as an absorbing layer material for thin-film solar cell.The Hall effect results at room temperature that CZTS and Ni-substituted（x=0.5,1）samples have good electrical conductivity,and Ni-substituted samples have better electrical conductivity than pure CZTS.The electrical properties of Co-substituted samples are slightly worse than pure CZTS and Ni substituted samples.