Sb₂Se₃ Thin-film Solar Cells:Film Preparation,Device Characterization And Photovoltaic Performance Optimization

As the energy crisis and environmental pollution are increasing,people pay more attention to renewable energy generation technology especially photovoltaic.At present,crystalline silicon solar cells are approaching the practical limit of power conversion efficiency,however,the difficulty to make them flexible limits their application scenarios.III-V solar cells represented by Ga As demonstrate outstanding solar-to-electricity performance,but are difficult to be widely used due to the prohibitive manufacturing cost.Cd Te and CIGS thin-film solar cells are still facing toxicity and high price of raw materials,which restrict their further development.Therefore,developing high-efficiency,cheap and flexible solar cell technologies is necessary to meet the requirements of various application scenarios.Antimony selenide(Sb₂Se₃),as an emerging kind of inorganic photovoltaic material,having the advantages of suitable bandgap(about 1.1 e V),high theoretical efficiency limit(>30%),large absorption coefficient(>10⁵ cm^-1 in visible wavelength region),one-dimensional chain-like crystal structure enabling outstanding flexibility,abundant and low price of raw materials,is advantageous for developing high-efficiency and low-cost thin-film solar cells.Within merely six years,the power conversion efficiency of Sb₂Se₃ thin-film solar cells was elevated from 2.26%to 9.2%.Nevertheless,the large open-circuit voltage deficit(>0.65 V)is still the main bottleneck for the development of Sb₂Se₃ solar cells.Additionally,systematic studies focusing on the open-circuit voltage of Sb₂Se₃ solar cells are absent so far.There are two main reasons:first,the research on Sb₂Se₃ thin-film solar cells started only very recently;second,open-circuit voltage is affected by various factors and difficult to investigate.This dissertation aims at lifting the open-circuit voltage of Sb₂Se₃ thin-film solar cells from the interface,film quality and device perspective with a combined theoretical and experimental studies.The research includes the following three parts:(1)In situ synchrotron radiation high-resolution photoelectron spectroscopy was introduced to systematically investigate the interfacial properties of Cd S/Sb₂Se₃,Zn O/Sb₂Se₃,and Ti O₂/Sb₂Se₃ heterojunctions.Combined with in situ photoelectron spectrum and theoretical thermodynamic calculations,the interfacial reaction and transition layer thickness were evaluated quantitatively.Furthermore,the conduction band offsets of different heterojunctions were calculated,which explained the relationship between the types of buffer layer and device performance.The results imply that Cd S/Sb₂Se₃heterostructure is most suitable for developing high-efficiency solar cells,which laid the foundation for the subsequent photovoltaic preparation.(2)Because of the one-dimensional chain-like crystal structure,external elements is difficult to enter into the[Sb₄Se₆]_n ribbons and be activated.Thus,we innovatively used Pb with a large atomic radius to increase the probability of substitutional doping.The hole concentration of Sb₂Se₃ film prepared by vapor transport deposition was elevated from 10¹³cm^-3 to over 10¹⁵ cm^-3due to the introduction of Pb dopants.We thus proposed that the atomic radius has a direct influence on the doping effect was proposed,which was confirmed by a series of doping experiments utilizing IV group elements.This study paves the way for follow-up device preparation and optimization.(3)The above experiences were extended to the study of antimony sulfide selenide alloyed thin-film solar cells.Owing to the intersolubility of antimony selenide and antimony sulfide,single-source vapor transport deposition and hydrothermal method were both developed for preparing antimony sulfide selenide films.Based on a deep-going understand of film growth mechanisms,via reducing the film growth velocity and optimizing the film quality,antimony sulfide selenide thin-film solar cells with a strong built-in electric field and low defect concentration were successfully fabricated using Cd S as the buffer layer.Through restraining the nonradiative recombination and lowering the reverse saturated current density,the device performance was significantly improved,achieving a high open-circuit voltage of 0.647 V and power conversion efficiency of 10.01%.