【作者】 张悦；

【导师】 翟天佑；

【作者基本信息】 华中科技大学 ， 材料学， 2022， 博士

【摘要】 二维金属磷硫属化合物具有丰富的种类、独特的晶体结构以及新奇的物理性质,已成为未来光电器件领域的理想候选材料。探索新型的二维金属磷硫属化合物,研究其本征物理、化学性质,并在此基础上构筑高性能光电器件,具有重要意义。SnP₂S₆是一种非中心对称结构的层状半导体,具有低的解理能(～0.24 J m^-2)、合适的禁带宽度（～2.23 e V）、高的载流子迁移率(～150 cm² V^-1 s^-1)、强的光吸收效率(～10⁶cm^-1)以及良好的动力学和热力学稳定性,这些优异的性质使其成为高性能光电器件的良好载体。然而,目前高质量的二维SnP₂S₆晶体仍缺乏有效的制备工艺,并且其光物理机制尚不明朗,这严重制约了其在光电器件领域的应用。基于此,本论文从高质量二维SnP₂S₆晶体的制备出发,详细研究其晶体结构、光学性质和光电性能,并且探索了二维SnP₂S₆晶体在光电探测器中的应用,主要研究内容如下:（1）二维SnP₂S₆晶体的制备及其非线性光学性质研究。结合化学气相输运法和机械剥离法制备了高质量的二维SnP₂S₆晶体。空间反演对称性破缺的二维SnP₂S₆晶体同时具有二阶和三阶非线性光学响应,且响应不受奇/偶层的限制,呈现出宽带光谱响应的特点。在810 nm的激发波长下,二维SnP₂S₆晶体的二阶磁化率可达4.1×10^-9 m V^-1,比大多数二维材料高1-2个数量级。此外,偏振敏感的二阶非线性光学响应表明二维SnP₂S₆的晶体结构具有三重旋转对称性,其面内扶手椅方面具有最大的偶极矩,对应于最强的非线性光学响应。（2）二维SnP₂S₆晶体的自陷态激子发光性质及其光电探测性能研究。利用稳态、瞬态光吸收和光致发光光谱研究二维SnP₂S₆晶体的光与物质相互作用。由于晶格中存在畸变的[Sn S₆]^8-和[P₂S₆]^4-八面体以及强的电-声耦合,该晶体表现出独特的自陷态激子发光性质,其动力学过程在10¹-10³ ps。基于二维SnP₂S₆晶体的光电探测器在300-600 nm波长范围内具有显著的光响应。此外,由于自陷态诱导产生的光栅效应,该器件在365 nm激发光下的响应度和探测度可达22.8 A W^-1和4.0×10¹⁰ Jones。（3）二维SnP₂S₆/（PEA）₂Pb I₄异质结的构筑及其光电探测性能研究。利用具有高光吸收的钙钛矿（PEA）₂Pb I₄与二维SnP₂S₆晶体复合,构筑具有II型能带排列的二维SnP₂S₆/（PEA）₂Pb I₄异质结光电探测器。该异质结器件不仅具有增强的光吸收和光电转换效率,还促进了光生载流子在异质结界面处的快速分离与转移,从而实现了兼具高灵敏度和快响应速度的光探测性能。该异质结器件在365 nm激光照射下的响应度、探测度和外量子效率分别可达67.1 A W^-1、2.8×10¹¹ Jones和22 825%,光响应时间和衰减时间分别为30μs和120μs。更多还原

【Abstract】 On account of rich species,unique crystal structures and novel physical properties,two-dimensional metal phosphorus chalcogenides（2D MPCs）have become ideal candidates for future optoelectronic devices.It’s of great significance to explore new 2D MPCs,study their physical and chemical properties,and then build high-performance optoelectronic devices on this basis.SnP₂S₆ is a layered semiconductor with non-centrosymmetric structure,which possesses low cleavage energy(～0.24 J m^-2),moderate band gap（～2.23 e V）,high carrier mobility(～150 cm² V^-1 s^-1),strong light absorption efficiency(～10⁶ cm^-1)as well as excellent kinetic and thermodynamic stability.These unique properties make it a good carrier for high-performance optoelectronic devices.However,up to present,the high-quality 2D SnP₂S₆ crystal still lack effective preparation technology,and its photophysical mechanism is still unclear,which seriously restrict its application in the field of optoelectronic devices.For that reason,this thesis starts from the preparation of high-quality 2D SnP₂S₆ crystal,and then studies its crystal structure,optical properties and optoelectronic characteristics in detail.In addition,the device applications of2D SnP₂S₆ crystal in photodetectors have been explored.The main research contents are as follows:（1）Preparation and nonlinear optical property of 2D SnP₂S₆ crystal.2D SnP₂S₆ crystal with high crystalline quality was prepared by combining chemical vapor transport and mechanical exfoliation.The 2D SnP₂S₆ crystal with broken inversion symmetry has both second-order and third-order nonlinear optical responses,and the responses are not limited by odd/even layers,showing the characteristics of broadband spectral responses.The second-order polarizability of 2D SnP₂S₆ crystal reached up to 4.1×10^-9 m V^-1 at 810 nm,which is 1-2 orders of magnitude higher than that of most reported 2D materials.Furthermore,the polarization-sensitive second-order nonlinear optical response indicates that the crystal structure of 2D SnP₂S₆ possesses triple rotational symmetry with the largest dipole moment in its in-plane armchair aspect,corresponding to the strongest nonlinear optical response.（2）Self-trapped exciton emission property and photodetection performance of 2D SnP₂S₆ crystal.The light-matter interaction in 2D SnP₂S₆ crystal was studied by steady-state,transient optical absorption and photoluminescence.Due to the presence of distorted[Sn S₆]^8-and[P₂S₆]^4-octahedrons and strong electron-phonon coupling,2D SnP₂S₆ crystal exhibites unique self-trapped exciton emission property,with the dynamic process of 10¹-10³ ps.The photodetector based on 2D SnP₂S₆ crystal demonstrated a broadband detection capability from 300 to 600 nm.In addition,due to the photogating effect induced by the self-trapped exciton,the responsivity and detectivity of the 2D SnP₂S₆-based photodetector under 365 nm illumination were 22.8 A W^-1 and 4.0×10¹⁰ Jones,respectively.（3）Fabrication and photodetection of 2D SnP₂S₆/（PEA）₂Pb I₄ heterojunction.2D SnP₂S₆/（PEA）₂Pb I₄ heterojunction with type-II band alignment was fabricated by combining strong-optical-absorption perovskite（PEA）₂Pb I₄ with 2D SnP₂S₆ crystal.The combination not only improved the optical absorption efficiency and photoelectric conversion efficiency of the 2D SnP₂S₆/（PEA）₂Pb I₄ heterojunction,but also promoted the separation of photogenerated electron-hole pairs at the heterojunction interface.Thus,the photodetection performance with high sensitivity and fast response rate was realized.Under365 nm laser illumination,the responsivity,detectivity and external quantum efficiency of the 2D SnP₂S₆/（PEA）₂Pb I₄ heterojunction reached up to 67.1 A W^-1,2.8×10¹¹ Jones and 22825%,respectively.Besides,the response time and decay time are 30μs and 120μs,respectively.更多还原