Study On The Cu₂MSnS₄(M=Co²⁺,Ni²⁺,Zn²⁺) Nanocrystals Thin Films Fabricated By The Solution Processes And Selenized Thin Films

?_<sup>2-?-?-?₄ semiconductor materials with suitable direct band gap,high absorption coefficient,low-cost eco-friendly raw materials and abundant selection of chemical element(such as I= Cu⁺,Ag·+,Li⁺;II= Zn²⁺,Co²⁺,Ni²⁺,Cd²⁺,Fe²⁺;IV= Sn⁴⁺,Ge⁴⁺;VI= S^2-,Se^2-),are ideal substitution for preparation of inorganic thin film photovoltaic devices.The most typical compound is Cu₂ Zn Sn?S,Se?₄?CZTSSe?with kesterite structure.Recently,Mitzi research group of IBM?USA?has fabricated CZTSSe solar cell by hydrazine-based solution method achieving the highest power conversion efficiency of 12.6%.However,the study on transition metal element substituted for zinc element in CZTS,and simple and eco-friendly non-hydrazine method to fabricate the CZTSSe solar cells is not sufficient.Our paper focused on fabrication of Cu₂ Co Sn S₄?CCTS?and Cu₂ Ni Sn S₄?CNTS?thin films and developing dithiocarbamate-based solution methods to fabricate eight CZTS precursor solutions.We obtained original achievements as follows.Firstly,we utilized dithiocarbamate-based solution approach to fabricate highquality CCTS and CNTS nanocrystal thin films.The compositions,band gaps and structures of CCTS and CNTS nanocrystal thin films were studied.Then,we selenized CCTS and CNTS nanocrystal thin films at high temperature.We found that during process of selenization,the CCTS and CNTS nanocrystal thin films are oxidized by selenium steam and actively formed the Cu₂Sn?S,Se?₃,Co?S,Se?₂ and Ni?S,Se?₂.Thus,the selenized CCTS and CNTS nanocrystal thin films are phase-separated and cannot form the pure phases of Cu₂ Co Sn?S,Se?₄?CCTSSe?and Cu₂ Ni Sn?S,Se?₄?CNTSSe?nanocrystal thin films.We successfully fabricated photodetector devices by CCTS and CNTS nanocrystal thin films and demonstrated the excellent photoelectric performance under the intermittent illumination of simulated sunlight,which shows the CCTS and CNTS nanocrystal films have a potential application in nanocrystal-based thin film solar cells.Secondly,butyldithiocarbamic acid-based solution approach is a typical method to fabricate metal sulfide semiconductor thin films.Because the butyl can be substituted by the other functional group and this solution approach can be effectively extended,which are superior to other solutions.We successfully prepared the dithiocarbamatebased CZTS precursor solutions using the various amino groups,such as methylamine,ethylamine,propylamine,butylamine,amylamine,hexylamine,octylamine and ethanolamine.These solutions showed the distinct wetting behavior and stability.We fabricated the CZTS nanocrystal thin films by a simple spin-coating and annealing process.We studied the thermogravimetric analysis of the precursor solutions and structures of as-prepared CZTS films,and investigated the compositions,structures and microstructure performance of selenized CZTS thin films.After high temperature selenization,CZTS nanocrystal thin films fabricated by fat alkyl amine are phaseseparated.However,the CZTSSe thin films fabricated by the ethanoldithiocarbamatebased CZTS precursor solution are high-quality,and we achieved the best power conversion efficiency of 7.66% under 1.5 AM illumination by this thin film as absorb layer.In this thesis,we investigated the research progress of ?_<sup>2-?-?-?₄ semiconductor materials systematically.We study the fabrication of CCTS and CNTS nanocrystal thin films and photoelectric performance of these thin films.And we also extended the butyldithiocarbamic acid-based solution approach by a versatile strategy.Our work provided the new outlook of materials fabricated by transition metal element substituted for zinc element of CZTS and fabricating CZTSSe solar cells by solution methods.We provide the useful experimental data for further study of ?_<sup>2-?-?-?₄ semiconductor materials.