A Solvothermal Proceess To Copper Znic Tin Sulfide Nanocrystals And Their Application

Copper indium selenide (CIS) or copper indium gallium selenide (CIGS) and cadmium sulfide are perfect materials for fabricating solar cells, and CIGS have a high conversion efficiency. Comparing with CIGS, each components of copper zinc tin sulfide (CZTS) are abundant in earth’s crust, and easy to be fabricated in a large scale. CZTS has a tunable direct band-gap energy ranging from1.0～1.5eV and a high absorption coefficient, It receives increased attention as next generation absorption material in the past few years. Comparing to expensive vacuum method, non-vacuum solvothermal method attracts much more research interests as a low-cost absorber layer deposition. Meanwhile, as one of the metal chalcogenide, layered CZTS can support fast Li ion conduction and low transition metal oxidation states. Though their cycle stability is not very good, the layered CZTS is still one kind of promising anode materials for lithium ion batteries. The main contents are summarized as follows:We successfully synthesized the CZTS NCs through a solvothermal method. We used CuCl2, ZnCl2, SnCl4, thiourea as raw materials, and synthesized three different CZTS NCs with PVP, OP-10, and without any surfactant. This method is simple, easy operated, low-cost, nontoxic, without harsh conditions, such as vacuum or inert atmosphere protection, high temperature, high pressure and so on. The crystallographic information, morphology, thermal behavior, semiconductor property were investigated using XRD, FE-SEM, DSC, UV. From the UV-vis spectroscopy, the band-gap energy was1.3eV,1.5eV,2.2eV corresponding to CZTS NCs synthesized with PVP, OP-10, without using any surfactant, we successfully adjusted the band-gap energy of the CZTS NCs.In the experiment of synthesis of ternary chalcogenide compound, we got a mixture of CuS and ZnS when the precursor of CuCl2, ZnCl2, thiourea were used. On the other hand, we got a ternary chalcogenide compound called Cu2SnS3as the CuCl2, SnCl4, thiourea precursor were used. Furthermore, the band-gap energy of the semiconductor has been in the1.8-2.4eV range with the composition changing from to Cu2ZnSnS4. We could successfully controll the band-gap energy of the semiconductor by changing the amount of the znic element, so that the semiconductor could be further applied in solar cell field.Layered SnS2, flower-like Cu2ZnSnS4were synthesized by low-cost solvothermal approach. The electrochemical properties of the lithium ion batteries were characterized with cyclic voltammograms (CV) and charge and discharge curve under constant current. It showed that the coulombic efficiency of the SnS2lithium ion battery was up to98%at the35cycles, and the capacity of the lithium ion battery was375mAhg-1under the condition of the current density of50mAg-1, but after35cycles, the coulombic efficiency dropped to96～97%, the stable capacity of SnS2was257mAhg-1, only25%of the initial capacity at the50th cycle.Under the same condition, the stable capacity of Cu2ZnSnS4was210mAhg-1, only23%of the initial capacity at the50th cycle. To further study the electrode reaction mechanism of the SnS2, CuS, ZnS lithium ion batteries, we got the electrode reaction mechanism of Cu2ZnSnS4lithium ion battery. The Cu2ZnSnS4NCs decomposed in the presence of Li ion, the charge and discharge curve was similar to the equivalent of CuS, ZnS, SnS2, and this could help us better understand the performance of Cu2ZnSnS4lithium ion batteries.