Absorber Regulation And Interface Modification For Antimony Chalcogenides Solar Cells

Antimony chalcogenides Sb₂S₃ and Sb₂（S,Se）₃ have been widely studied in the field of photodetectors and solar cells due to their high absorption coefficient,high carrier mobility and long carrier diffusion length.Compared with copper indium gallium selenide and cadmium telluride,their constituent elements have abundant storages in the earth and they are also non-toxic.In addition,they have single crystal phase.However,they have a quasi-one-dimensional crystal structure,leading to anisotropy of physical properties,which are greatly affected by crystal orientation.Moreover,the materials have numerous deep level defects,which are prone to form deep level recombination centers.It can hinder the further improvement of device performances.The current record efficiency of antimony chalcogenides is only 10.7%,which is far lower than the predicted value of Shockley-Queisser limit.In addition,the common antimony chalcogenides solar cells usually use organic molecule 2,2’,7,7’-Tetra[N,N-bis（4-methoxyphenyl）amino]-9,9’-spirobifluorene（spiro-OMe TAD,abbreviated as spiro）as the hole transport layer,which has poor stability.Thus,there is still a long way from commercialization.This paper takes the antimony chalcogenides semiconductor materials Sb₂S₃ and Sb₂（S,Se）₃ as the research core.It is aimed to solve the remaining scientific problems in the field.In this dissertation,we designed and optimized the solar cells from different perspectives to obtain antimony chalcogenide solar cells with excellent performance and good stability.Firstly,magnesium-doped tin dioxide nanocrystals were successfully prepared by sol-gel method.The film was inserted as a buffer layer between FTO and Cd S by spin-coating method to construct SnO₂/Cd S/Sb₂S₃ gradient heterojunctions,making a better band energy level alignment.The crystal orientation growth of Cd S can be regulated by further optimizing the concentration of precursors and the proportion of Mg element.And the surface morphology,crystalline characteristics and optical absorption characteristics of the upper light-absorbing material can be improved.Thus,the antimony sulfide film shows more compact surface with larger grains and fewer pinholes.The quality of the heterojunction was improved by introducing Mg-doped SnO₂ buffer layer.It can also promote the transport and extraction of carriers,resulting in the improvement of efficiencies of antimony sulfide solar cells.Consequently,solar cells achieved the champion efficiency of 6.31%.Secondly,considering the relationship between the highest efficiency and band gap according to the the Shockley-Queisser limit theory,the efficiency can reach up to 32%when the band gap is about 1.4 e V.So,selenium element can be added into antimony sulfide to adjust the band gap.We optimized the hydrothermal growth time,hydrothermal temperature and the content of added selenourea to prepare sulfoselenide solar cells with excellent performance.However,due to the existence of a number of deep energy level defects,antimony sulfide selenide is prone to form a deep level recombination center,resulting in serious recombination of carriers and hindering the improvement of device performance.In order to solve the problem,potassium iodide was used to treat the surface of antimony sulfoselenide via hydrothermal method.It can improve the surface morphology of the film,regulate the crystal growth orientation of the absorbing layer,promote the favorable[hk1]orientation and enhance the carriers’transport.More importantly,the freely moving iodine ions can occupy the original Se or S vacancies and inhibit the formation of deep level antistie defects(Sb_（S,Se）).It further reduced the density of deep level defects,leading to the reduction of carriers’recombination and effective improvements of the device photoelectric performances.Finally,in view of the problems of high price and poor stability of spiro,which is now commonly used in Sb₂（S,Se）₃ solar cells as organic hole transport material,nickel oxide（Ni O）was used as the inorganic hole transport layer.What’s more,the surface of Ni O was treated by tin monosulfide quantum dots,and the film has higher conductivity after surface treatment,and forms a better energy alignment with the antimony sulfoselenide absorbing layer.It can promote the transport and extraction of hole carriers and thus improves the performance of all-inorganic antimony sulfoselenide solar cells.In addition,compared with spiro-based solar cells,the prepared inorganic solar cells have higher thermal stability,humidity stability and long-term stability.