Cu₂ ZnSnS₄ Nanocrystals By Solution Chemical Synthesis And Its Colloidal Ink Thin Films

Nowadays, with the increasing of energy exhaustion and environment pollution, the application of new energy resources has become a hotspot of the whole world. With the advantage of non-pollution and inexhaustibility, solar photovoltaic power generation has got rapid development. Cu₂ZnSnS₄ with kesterite structure is a typicalⅠ2-Ⅱ-Ⅳ-Ⅵ4 chalcogenide semiconductor and good solar absorber material. It has a direct band-gap of 1.45-1.50 eV which matches well with the solar energy spectrum and high light absorption of about 104cm-1. In addition, the buildup elements of the kesterite compound are non-toxic , pollution-free and abundant in the crust, all which will be able to lead to reduced production cost and less environment pollution for solar cell manufacture.In this paper, the Cu₂ZnSnS₄ nanocrystals are synthetized by solution chemical method and its colloidal ink thin films are made by dip-coating method. The cationic source with the mixture of Cu(NO₃)₂,Zn(NO₃)₂ and SnCl₂ is injected into the precursor solution with the sulfur source, complexing agent, dispersing agent and reducing agent at a high temperature to prepare the Cu₂ZnSnS₄ nanocrystals. The products are characterized by EDS, XRD, TEM, SEM and UV-Vis to study the impacts of the elements ratio, injection temperature, refluxing time, complexing agent, dispersing agent and injection styles.Experimental results show that when the precursor solution with Cu²⁺(0.01mol/L), Cu:Zn:Sn:S=2:1.4:1:12 and citric acid(0.2522g), is injected into the thioacetamide solution added by glucose(0.1g) and PVP (0.2 g) at 290℃and refluxed for 20min, the Cu₂ZnSnS₄ nanocrystals whose elemental composition is close to the ideal stoichiometric ratio can be synthesized. And the synthesized nanocrystal ink has good dispersion and optical properties. When the dip-coated film is heated at 400℃for 20min, the crystalline and densification could be improved. But when the temperature is too high (>500℃), the stoichiometry becomes imbalance which may be caused by decomposition reaction at high temperature.