| CFTS(Se),derived from CIGS by elements changing of In,Ga to Fe and Sn,have been considered to be promising photovoltaic materials due to its analogous crystal structures to CIGS,suitable band gap,abundant and less toxic elements.On account of the rare reports about CFTS(Se)in the previous literatures,in this paper,study from the preparation of CFTS(Se),we investigate the basic-physical properties of CFTS(Se)systematically and then develop it to the application of device.During these periods,some innovative achievements have been obtained:1.CFTS(Se)thin films with pure phase,big grain size and appropriate band gap have been prepared by sputtering and sol-gel method.In addition,the band structure of CFTS(Se)has been studied using the first-principles calculation.The results show that CFTS(Se)is a direct band gap semiconductor and electron transition between band mainly occurs in Cu 3d and Fe 3d/Sn 5s orbit.Magnetron sputtering combined with RTP process has been employed for synthesizing CFTS(Se)thin films.Results show that,the as-deposited thin films are successfully indexed by the standard XRD pattern of CFTS(Se),with the tetragonal stannite structure and space group of 1-42m.SEM shows that the surface of as-deposited thin films is dense and smooth,which is in favour of improving the performance of device.The band gap of CFTS is 1.42 eV and CFTSe is 1.16 eV.At the same time,CFTS thin films with larger grain size compared with sputtering method,dense and smooth surface have also been prepared by Sol-gel method,which band gap is 1.62 eV.Sol-gel method makes the preparation of CFTS more facilitation.Moreover,it provides solutions for elements doping of CFTS quaternary semiconductor.In order to further understanding the CFTS,the band structure and density of states(DOS)of CFTS(Se)has been studied using the first-principles calculation.The results display that CFTS(Se)is direct band gap and electron transition between band mainly occurs in Cu 3d and Fe 3d/Sn 5s orbit.2.Confirmed the growth mechanism of CFTS by changing the annealing process and analyzed the structure phase transition during the grain growth of CFTS.Results show that metastable CFTS-rhodostannite will be formed at low temperature condition,moreover,wavenumber of 323.8 cm-1 for its Raman A1 frequence has been calculated.The related empirical model and formula have also been obtained.Series of studies have been carried out to research the physical properties of CFTS(Se).The growth mechanism of CFTS has been determined,which involved three steps:binary phases for the first,ternary compound for the second and then quaternary semiconductor for the last.Besides,the structure phase transition of CFTS has been detected during the grain growth.The structure of CFTS transforms rhodostannite to stannite with annealing from low temperature to high temperature,which can contribute to avoid the formation of metastable rhodostannite phase.It has certain help to improve the property of CFTS.The information of Raman on CFTS-rhodostannite is also provided by calculation combined with experiment.The stress and dislocation density of CFTS(Se)are both confirmed as "U" model with the specific process condition.At the same time,the growth energy of crystal plane of CFTS(Se)is qualitatively analyzed to put forward the plan of crystal orientation control.Results show that grain growth along(220/204)-orientation becomes largest when holding time is 15 min,and it will spontaneous decomposition into(112)facets for further extending holding time.In this paper,the empirical formula of Cu-Se bond length for CFTS(Se)is obtained by optimizing the that of CIS.3.Elements doping for preparing multiternary semiconductors CFZTS and CFTSSe.Results show that transition of structure phase,inhibition of grain growth and shift of band structure have been detected with increasing Zn content in CFZTS thin films;Furthermore,for CFTSSe,the relationship between structure,morphology,optical properties and the ratio of Se/S has been studied systematacially.CFZTS and CFTSSe thin films have been synthesized by Sol-gel doping method.Structure phase transition of CF1-xZxTS form ST to KT has been observed when 0.5<x<0.75.Furthermore,the more doping of Zn the small grain size of CFTS,meaning the Zn2+ will restriain the grain growth of CFTS.Straightly speaking,the growth energy of crystal plane of CZTS is larger than that of CFTS.And then,on the basis of Hund's rule and electron transition theory,we analyzed the electronic redistribution inducing the change of band structure of CFTS caused by the Zn doping.Transmission spectra show that the conduction band of CFTS is away from the band gap with the Zn doping.For another,Se element is not only can make the band gap of CFTS more tunable but also may alter the structure of CFTS,such as:band gap of parabola type,expansion of Cell volume,change following Vegard's law of lattice constants and low wavenumber offset of Raman peaks with increasing Se element in CFTS thin films.In this paper,the alloying mechanism of CFTSSe has also been studied in detail,which coexistence in the form of solid solution(CFTS-CFTSe).4.Formation of back electrode,buffer layer,window layer and CFTS(Se)thin film solar cells to confirm the application feasibility of CFTS(Se)material in photovoltaic field.Furthermore,the influence of annealing process(heating rate)on CFTS(Se)thin film solar cells have been investigated.In this paper,the Mo back electrode and window layer is formed by sputtering method.The thickness of Mo layer is around 1 um and columnar growth pattern has been observed.The square resistance of Mo in this experiment is 0.3?/?.The optimal growth condition for i-ZnO is 0.4 Pa,30 W and for AZO is 0.2 Pa,150 W,with the thickness of 70 nm and 850 nm for i-ZnO and AZO,respectively.The transmittance of visible light is higher than 80%for all window layers,and the best performance of square resistance for AZO is 135 ?/? in this experiment.The buffer layer is prepared by Sol-gel method with larger grain size and cratered surface.CFTS(Se)thin film solar cells have been obtained by magnetron sputtering and Sol-gel method,respectively.The highest open circuit of all the as-fabricated solar cells is 0.216 V with the best performance of 0.265%.Furthermore,for magnetron sputtering method,the influence of annealing process(heating rate)on CFTS(Se)thin film solar cells have been investigated,too. |
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