| Kesterite Cu2ZnSn(S,Se)4(CZTSSe)thin-film solar cells have drawn extensive research interest due to the high absorption coefficient,suitable band gap,and low price of constituent elements during the past few years.To obtain high-efficiency CZTSSe thin film solar cells,researchers have developed a variety of methods for preparing the CZTSSe light-absorbing layers,which are mainly divided into two categories:the vacuum-based method and the solution-based method.Compared with vacuum-based method,solution-deposited method is low cost,simple operation and easy to scale production,so the solution-based approach is widely used in the research of CZTSSe thin film solar cells.Solution approaches are mainly including hydrazine-based method,dimethylsulfoxide-thiourea method,mercaptan-amine method,carbon disulfide-butylamine method;however,these widely used solution approaches are usually having unpleasant odors,toxic,polluted,and not meeting the green chemical requirements;besides,they are not conducive to popularization and application and large-scale production.So it is very crucial to discove a green and environmentally friendly solution method for the application of CZTSSe thin-film solar cells.In this work,we developed a green and environmental friendly solution approach of butylamine-butyric acid ionic liquid,which was applied to fabricate the high quality of Cu2ZnSn(S,Se)4 thin film solar cells.The specific work contents are as follows:1.In this research,a green and environmentally friendly molecular precursor solution method has been developed to prepare Cu2ZnSn(S,Se)4 thin film solar cells.Here,Cu2O,ZnO,SnCl2,and thiourea are selected separately as the copper source,zinc source,tin source,and sulfur source,and they are dissolved in the n-butylammonium butyrate ionic liquid to prepare the Cu2ZnSnS4 thin film.We found that liquid n-butylammonium butyrate can dissolve a number of metal oxides,metal chlorides,metal nitrates and metal acetates.Thermally degradable n-butylammonium butyrate can be completely removed by a low-temperature sintering process,forming high quality Cu2ZnSnS4 nanoparticle thin flm.By changing the selenization time and temperature,we obtained the best selenization condition,which is 540? for 10 min,and high-quality of Cu2ZnSn(S,Se)4 light-absorbing layer was obtained in this selenization conditions.Finally,a power conversion effciency of 8.79%is obtained by this facile and green solution approach.In addition,we also use this general ion liquid-assisted approach to prepare various metal sulfide films.2.In this work,a facile and effective method to remove the small particle layer in the light-absorbing layer of Cu2ZnSn(S,Se)4 was developed.We found that the small particle layer faded away by selenizing the Cu2ZnSnS4 precursor films,which were pre-annealed in the air.When the air-annealing temperature rose to 500?,the small particle layer would be completely disappear.Annealing the CZTS films in air not only makes the Na ions to diffuse from the soda lime glass into the precursor CZTS films,but also leads to the surface phase separation of the prefabricated CZTS precursor films,which is contributing to improving the crystal quality of aCu2ZnSn(S,Se)4(CZTSSe)thin films.Under the selenization conditions of 500?for 10 minutes,we obtained the CZTSSe light-absorbing layer with grain penetration.And the short-circuit current,open-circuit voltage and fill factor all were enhanced.As a result,a photoelectric conversion efficiency of 9.80%was achieved by this method.3.As known,silver doping is a simple and effective way to improve the efficiency of CZTSSe thin-film solar cells.After being doped with silver,Ag will replace the Cu position in Cu2ZnSn(S,Se)4,which can effectively suppress Cuzn defects and help increase the open circuit voltage of the battery.So we studied the effect of silver ion doping on the CZTSSe thin film solar cell in this work.By optimizing the selenization conditions and doping concentrations,high-quality of CZTSSe light-absorbing layers were obtained.Compared with the devices without Ag doping,the photoelectric conversion efficiency of Ag-doped CZTSSe solar cell increased from 9.9%to 10.47%with a 5%doping concentration.4.In this research,the effect of Ge4+ion doping on the efficiency of CZTSSe thin film solar cell was studied.By introducing GeC14 to partially replace SnCl2 when preparing the precursor solution,we obtained the as-deposited CZTS films containing Ge4+ions after spin coating.By optimizing the selenization conditions,we obtained the ideal CZTGeSe light-absorbing layer film.We observed that the crystal size of the CZTSSe film beccame larger after the introduction of Ge4+.Ge4+ions can play a critical role in increasing the open circuit voltage of the device.Compared with non-doped Ge4+devices,the open circuit voltage and short-circuit current of the devices with Ge4+ dopinghave been improved,and the PCE has also increased from 9.76%to 10.28%. |
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