| The global energy shortage and the desire of renewable energy sources make new demand for more efficient and cost effective use in solar energy especially the optical properties of semiconductor materials.There has been a lot of interest in using copper zinc tin selenide(Cu2Zn Sn Se4,CZTSe)and copper zinc tin sulfide(Cu2Zn Sn S4,CZTS)for solar films.The band gap of CZTSe is about 1.0 e V to 1.50 e V and that of CZTS is about 1.30 e V to 1.50 e V,which both closely match the solar spectrum.Because their absorption coefficients are up to 104 cm-1,both CZTSe and CZTS are considered to the most promising new solar energy absorption materials.At present,the technologies for CZTSe and CZTS are under a rapid development.However,the same issues for all these methods are high cost of equipment,toxicity and harmful by-products during the preparing processings.And the processing technologies are more expensive.In this disseration,a new sol-gel procedure for preparing CZTSe and CZTS film is proposed based on the low equipment investment and energy consumption and present sol-gel methods in accordance to the existing problems in the processings.The mild conditions in the processs are included: non-toxic small molecule reaction reagent,reactants directly mixed and coated processing,the non-vacuum wind drying oven heating treatment,250 ? low temperature annealing conditions.For the preparation of CZTSe and CZTS films,the surface topography structure and optical performance analysis are used to characterize the absorption performance of this research.The main characteristics of this research are as follows.(1)The method includes inexpensive sources of copper,zinc,tin,and selenium,sulfur,such as copper(II)acetate,zinc acetate,tin(II)chloride,and zinc sulfide for the organic source material of low molecular weight substances,and copper(II)chloride dihydrate,zinc chloride,tin(IV)chloride pentahydrate,and zinc sulfide for the inorganic source material of low molecular weight substances.(2)All of the elements,including copper,zinc,tin,and selenium,sulfur,can be added at the same time,which simplifies the procedures and the processes.If the materials are mixed by a magnetic stirrer,they form a stable sol-gel precursor solution.A dry CZTS films can be prepared with a non-vacuum and at relatively low temperature(200-250oC).(3)Using safe,stable,and non-toxic zinc sulfide as the source of sulfur rather than the traditional,more toxic substances,such as hydrogen selenium and hydrogen sulfide,furthermore this method can avoid environmental pollution.The main content of this disseration are as follows.(1)The research mainly includes that the new sol-gel technology process is proper and universal through the preparation of the CZTSe and CZTS film.(2)And the characterizations of the film optical performances are detailed as follow.It is feasible to be applied in a wider range of light absorption from ultraviolet visible spectral region extended to the infrared region in the future.Firstly,CZTSe films were prepared by using a mild,non-vacuum,sol-gel procedure method from non-toxic selenide source.The organic small molecule Copper(II)acetate,zinc acetate reagents and inorganic small molecule reagents Copper(II)chloride,zinc chloride were used as reactants to prepare CZTSe films.Further,the optical properties of the film properties were analyzed from the differnent spectral effects.Sodium selenite and sodium selenite were the sources to prepare the four kinds of CZTSe films on the glass substrate.The band gaps lied in the range of 1.20 to 1.60 e V from the above four kinds CZTSe film under ultraviolet visible region.So they were proper to meet the requirements of the semiconductor optical absorption layer when the CZTSe films were applied to the photoelectric transformation.At the same time,there were not scattering from the Raman and back to inspire from photoluminescence.It was found that they were favarable to absorbing solar light from impure compositions existed in the CZTSe films from ultraviolet visible region extended to the infrared region.The band gap for the CZTSe films prepared from the inorganic group materials was 1.48 e V,which it is proper to meet the requirements of the semiconductor optical absorption layer when the CZTSe films were applied to the photoelect ric transformation.And it's worthy mentioning that it was suitable for light-absorbing material in wider spectral range.Subsequently,Copper(II)acetate,zinc acetate,tin(II)chloride and zinc sulfide from the small organic molecules were the sources.Low-cost CZTS films were prepared by using a mild,non-vacuum,sol-gel procedure method under non-toxic sulfide conditions.The preparation process was successful based on realization of the non-toxic vulcanization and low cost of CZTS film preparation.The CZTS films have smooth surface morphology and dense crystal particles.Further,the optical properties of the film properties were analyzed.In the range of visible light 400-1100 nm,the transmittance of the CZTS films is steady and the band gap is 2.32 e V by calculating and proposed cooperation figures,which is so higher than the ideal band gap range of solar energy absorption materials.And the deexcitation and Raman spectrum were not excited in the CZTS films.Because of impure composition s existed in the CZTS films,there were the absorption properties at the near infrared spectroscopy.It was demonstrated that it was beneficial to absorb sun light.At the same time,the impure compositions did not scatter and perform photoluminescence according to the experiment results.Based on the above findings,the films were showed to absorb light in a wider range of spectra in the range of infrared light regions of 2.5-15 ?m.It demonstrates that the CZTS films are considered to the promising new solar energy absorption material.Through the proper doping of calcium ions,the band gap width of the organic CZTS film is reduced from 2.32 e V to the optimum value 1.55 e V which is suitable for photoelectric transformation.Next,Copper(II)chloride dihydrate,zinc chloride,tin(IV)chloride pentahydrate,zinc sulfide for the inorganic source material of low molecular weight reagent substances.CZTS films were prepared by using a mild,non-vacuum,sol-gel procedure method.Further,the optical properties of the film properties were analyzed.The preparation process was also successful based on realization of the non-toxic vulcanization and low cost of CZTS film preparation.The film is composed of uniform and ordered dense sphere-like particles,which the observed particles were agglomerated in closely packed clusters to create dense,highly compact,and uniform films.Thus,it is favorable to absorbing light as a porous film with three-dimensional network structure.The zinc-rich CZTS film owned the crystallite size with Cu2 Zn Sn S4.When the thickness of the CZTS films lie in 5-16 ?m,the band gaps for the CZTS films prepared from the inorganic materials lie in 1.51 to 1.54 e V,which are matched in the band gap range of solar energy absorption(1.20 to 1.60 e V).Specifically however,the band gap for the CZTS films prepared from the inorganic materials lies in 1.45 e V,which is well matched in the optimal band gap range of solar energy absorption(1.45 to 1.50 e V).So the band gap width is appropriate for the application of photoelectric light absorption material from the inorganic-based copper zinc tin sulfur film by mild sol-gel process.However,they showed light absorption in a wider range of spectral ranges.Thu s,it is predictable to be applied in a wider range of light absorption in photovoltaic technology from ultraviolet visible spectral region extended to the infrared region.In this disseration,it is a successful method for the preparation of the absorbed CZTSe and CZTS films by using a mild,non-vacuum,sol-gel procedure.The method is proved to be in universal by many reactants from inorganic and organic reactants.In this processings to prepare the films,the small organic and inorganic substances as reactants are low-cost and without toxicity.Because of the simplification of procedures,CZTSe and CZTS films are directed to be prepared successfully and the films are considered to the potential promising new solar energy absorption materials.Some parameters such as Raman spectrum,fluorescence spectra,infrared spectrogram,photoluminescence spectrum are all to characterize the soalr absorption of the CZTSe and CZTS films besides of band gap width and light absorption coefficients.It can provide valuable reference to characterize the absorption from the solar in a wider spectrum.And the obtained CZTSe and CZTS films have light absorption in both the visible and the wider spectral range.In addition to the application of photoelectric convers ion,CZTSe and CZTS films have potential applications in absorbed sunlight situations especially in printing coating. |
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