Tunable Growth Of Full Stoichiometric CBTSSe Film And Its Application In Solar Cells

With the development of human society and the deteriorating ecological environment,solar energy,hydrogen energy and other clean and renewable energy have received global attention.Transition metal chalcogenides,as a new type of semiconductor materials,have attracted researchers' attention in the field of solar cells and photocatalysis,due to their excellent photoelectrochemical properties and physical-chemical properties.As a new generation of transition metal chalcogenide,Cu2BaSn(S1-xSex)4 not only has the advantages of abundant material,low cost,high absorption coefficient,and tunable band gap,but also overcomes the anti-site disorder in other metal chalcogenide(such as Cu2ZnSnS4).The conversion efficiency of single-junction Cu2BaSn(S1-xSex)4 solar cells have exceeded 5%in only one year,and the photocurrent density also reached 12.08 mA/cm2(0V/RHE),showing promising development prospects.Although researches based on Cu2BaSn(S1-xSex)4 are developing rapidly,most of the methods are still limited by high cost,physical methods with severe preparation conditions.Device efficiency based oil Cu2BaSn(S1-xSex)4 prapared by low-cost chemical solution methods is still low(only 1.72%and 10mA/cm2),and there is difficulty in growing full-stoichiometric Cu2BaSn(S1-xSex)4,which failing to take full use of its advantages.Therefore,finding a new chemical solution method to grow full-stoichiometric Cu2BaSn(S1-xSex)4 films still has high engineering research value.In this paper,a chemical solution method based on thionothiolic-acid-metathesis process is developed to grow full-stoichiometric Cu2BaSn(S1-x Sex)4 films,the properity with different S/Se ratios are investigated and their application in the field of solar cells are also studied.The main contents are as follows:Firstly,solution process for synthesizing Cu2BaSn(S1-xSex)4 film based on thionothiolic-acid-metathesis was proposed.The chemical reaction inside the precursor solution were studied.The study found that there is only metathesis reaction occurred between precursor and metal oxide.The TGA curve of the precursor shows that the decomposition temperature is about 250?,much lower than the crystallization temperature of Cu2BaSn(S1-xSex)4,which meets the requirements for obtaining high-purity Cu2BaSn(S1-x Sex)4 film.Secondly,high-quality Cu2BaSnSe4 film was synthesized by chemical solution process.The effects of different synthesis conditions(curing temperature,annealing temperature,and annealing time)on the quality of the films were studied.It was found that the film exhibited a weak crystalline characteristic of Cu2BaSnS4 after being cured;Curing at 280? and annealing at 580°C for 30 minutes were studied to be the best conditions.Films prepared under this condition had the highest crystallinity and the best continuity with a maximum grain size of 5 ?m.By characterizing the morphology and optical properties of the CU2BaSnSe4 film under optimal synthesis conditions,we found that the Cu2BaSnSe4 film has a direct band gap of about 1.70 eV,which is suitable for absorber.Thirdly,Cu2BaSn(Si-xSex)4 films with different selenization ratios were synthesized by vulcanizing and selenizing.The study found that with the increase of the selenization ratio of Cu2BaSn(S1-xSex)4 films,the band gap will decrease from 2.00 eV to 1.68 eV,and the grains will gradually grow bigger with the decreasement of roughness(from 48.6 nm to 36.8 nm).However,as the proportion of selenization continue increasing,the film structure will gradually change from P31 to Ama2 with the decrease of band gap(increase from 1.68 eV to 1.70 eV),and the grain grown smaller and roughness became bigger.Therefore,the ratio of sulfur and selenium has a crucial effect on the quality of Cu2BaSn(S1-xSex)4 films.Finally,solar cells were fabricated using the Cu2BaSn(S1-xSex)4 films synthesized by this method,and the performance was analyzed.With the increase of the selenization ratio(from 0 to 0.62),the overall performance of the solar cell increases,and reaches the highest when the ratio is 0.62.As the selenization ratio continues to increase(from 0.62 to 1),the effciency decreased accompanied by a decrease in Voc and Jsc.Therefore,in the case of single-junction solar cells,appropriate ratio of sulfur and selenium contributes to the improvement of solar cell performance.By analyzing the structure of Cu2BaSn(S1-xSex)4 solar cells,we found that ZnO is not the most ideal material for the electron transport layer.By comparison,we propose an optimization scheme using SnO2 instead of ZnO as the electron transport layer of the solar cell to optimize device performance.The experiment proves that using SnO2 as the electron transport layer,the Jsc of the Cu2BaSn(S1-xSex)4 solar cell Generally exceeds the existing research results,and the highest efficiency(2.01%)of the Cu2BaSn(S1-xSex)4 solar cell based on the chemical solution method has finally been obtained.