Preparation And Characterization Of Copper Iron Tin Sulfur (CFTS) Thin Film

The development of clean energy resources as an alternative to the fossil fuels,has become one of the most important tasks for researchers on modern science and technology in the 20th century.Among a wide variety of renewable energy sources,solar energy is the best alternative,suitable for meeting the energy demands of the modern society greatly.Cu(In,Ga)(Se,S)2(CIGS)and CdTe based solar cells with stable performance,high energy conversion efficiency(over 20%)have become one of research hotspots in the' field of photovoltaic.However,it contains such elements as indium and gallium,whose concentrations in the earths crust are scarce.And the high production cost limits their application.Recently,a quaternary compound Cu2FeSnS4 thin film is considered to be one of the most promising candidates.It has the same crystal structure with CIGS and its constituents are abundant in nature and non-toxic.In addition,Cu2FeSnS4 has a suitable optical band gap(Eg=1.20 eV-1.50 eV)and a high absorption coefficient over 104 cm-1.The highest CFTS thin film solar cells conversion efficiency is 8.03%up till the present moment.Compared with the CIGS solar cells,the promotion space is relatively large,so the study of CFTS films has a good prospect for development.The Cu2FeSnS4(CFTS)thin films were synthesized by electrochemical deposition method onto FTO glass substrates followed by a post-sulfurization.Plenty of exploration have been made to find the most suitable depositing condition for CFTS thin film.The CFTS was successfully prepared using potentiostatic mode at room temperature.The structural,valence state and optical propert:ies of the samples were analyzed by X-ray diffraction(XRD),Raman spectroscopy(Raman),Energy dispersive spectrometer(EDS),X-ray photoelectron spectroscopy(XPS),Mapping and Ultraviolet-visible-near-infrared spectrophotometer(UV-Vis-NIR Spectrophotometer).The results show that the annealing time and annealing temperature have great influence on the structure and optical properties.When the annealing time is 30 min and annealing temperature is 550? in nitrogen atmosphere,a relatively perfect property can be gained for the film.Also,the direct band gap energy for the as-preparative CFTS thin films is found to be about 1.48 eV,meeting the requirements of solar cell device production.Meanwhile,the Cu-Fe-Sn stacked metal precursors were deposited by RF magnetron sputtering on glass substrate(SLG)with a post-sulfurization treatment to prepare CFTS thin film.To explore the best deposition sequence,sputtering condition and annealing conditions.The structure of CFTS film was studied by X-ray diffraction(XRD)and Raman spectroscopy(Raman).The surface morphology and the element distribution uniformity of samples were analyzed by scanning electron microscope(SEM)and Mapping,respectively.The chemical states of each element in CFTS thin film are analyzed by X-ray photoelectron spectroscopy(XPS).Moreover,UV-Vis-NIR Spectrophotometer was used to measure and calculate the optical band gap of thin film.The results show that the different sputtering order has a great effect on the properties of the film.With metal precursors of stacked sequence of Fe/Sn/Cu and annealing temperature of 550?,the abtained thin film possess best adhesiveness,highest degree of crystallinity,smoothest surface and most uniform distribution of each element.Moreover,it shows an optical band gap of 1.47 eV,which show that CFTS is promising as absorbed layer material for photovoltaic applications.