| Defect engineering is essential to semiconductor photovoltaic devices.A comprehensive and in-depth understanding of formation mechanism of defect and reasonable defect control are conducive to efficient solar energy conversion.Quasi-onedimensional(Q1D)antimony chalcogenide Sb2S(e)3(Sb2S3,Sb2Se3 and Sb2(S,Se)3)is a class of emerging light-harvesting materials for the excellent optoelectronic properties.However,the current serious obstacle to the development of Sb2S(e)3 solar cells is the severe open circuit voltage(VOC)deficit caused by its trap(Shockley-Read-Hall)recombination.Therefore,it is imminent to acquire the basic knowledge and develop rational strategy to manipulate the defect properties of Sb2S(e)3.This thesis focuses on the fundamental understanding of the defect properties of Sb2S(e)3 photovoltaic materials,there are five chapters in this doctoral thesis.Chapter 1:The basic principles of semiconductor including definition of semiconductor,energy band theory and classification of defects are covered.The mechanism of carrier generation and recombination in semiconductor,especially the impacts of defects on carrier generation and recombination are elucidated.The common defect detection techniques are overviewed.Moreover,the material characteristic and defect research status of Sb2S(e)3 are summarized,and the main contents of the paper are proposed.Chapter 2:The relationship of deep-level defects with composition and structure in Sb2S3 is investigated.Sb-rich and S-rich Sb2S3 films are prepared by co-evaporation deposition,and deep-level defects in the films are characterized by deep-level transient spectroscopy(DLTS).The composition and structure dependent deep-level defects are revealed.There are three electron traps in Sb-rich and two hole traps in Se-rich films,respectively.Additionally,it is uncovered that the Q1D structure of Sb2S3 possesses tolerance of interstitial defects,thus,the influence of Sbi on carrier lifetime is minor.This research establishes the relationship between material processing,defect chemistry,carrier dynamics and solar cell performance,and gives a guidance for the development of efficient Sb2S3 solar cells.Chapter 3:The deep-level defects in non-stoichiometric Sb2Se3 films are studied.Similarly,Sb-rich and Se-rich Sb2Se3 films are prepared by co-evaporation deposition.Then DLTS analysis shows that deep-level defects in Sb2Se3 are greatly affected by the stoichiometry.There are two hole traps in Se-rich films.While there are one electron and one hole trap probed in the Sb-rich film,practically,they are attributed to the one amphoteric Sbse antisite defect.In particular,the Sbse defect possessing equivalent capability of trapping electron and hole is critical for charge recombination and solar cells performance.Additionally,it is noted that Sb2Se3 shows better defect properties and longer carrier lifetime only with stoichiometric or slight Se-rich composition.Chapter 4:The formation mechanism and the variation with Se/(S+Se)atomic ratio of deep-level defects in Sb2(S,Se)3 was investigated.Sb2(S,Se)3 films with different Se/(S+Se)atomic ration were prepared by hydrothermal deposition.DLTS analysis manifests there are three hole traps in the Sb2(S,Se)3 films corresponding to the Sbs antisite defects at three positions respectively,furthermore,the appropriate amount of Se can effectively passivate the deep-level defects in the film and inhibit the carrier recombination.This work enriches the fundamental understanding of defect properties in Sb2(S,Se)3.Chapter 5:The main contents of this thesis are summarized.Namely,experimental investigation of deep-level defects in Sb2S(e)3 is systematically carried out,and the formation mechanism of deep-level defects and their effects on carrier transport as well as device performance are revealed.The current issues of Sb2S(e)3 in terms of shallow-level defects manipulation,deep-level defect passivation and solar cell structure design are discussed,and the development of this class of solar cells is prospected. |
