【作者】 高燕；

【导师】 刘为为；

【作者基本信息】 华中科技大学 ， 光学， 2023， 博士

【摘要】 金属卤化物钙钛矿材料,由于其优异的光电特性,如大的吸收耦合系数、可调谐的光学带隙、较低的缺陷态浓度、高的缺陷容忍性以及较长的载流子扩散长度,在高性能光电器件领域显示出广阔的应用前景。铅卤钙钛矿本身的离子属性使得其对来自外界的压力、光照以及温度等因素相当的敏感,从而为钙钛矿光电特性的调控提供了丰富的手段。特别地,电场调控为钙钛矿光电特性的优化和调控提供了简便、有效的手段,对于提升钙钛矿材料和器件的光电性能具有重要意义。论文的主要内容如下:（1）制备了无机卤化铅钙钛矿材料CsPbBr₃及其复合结构,研究了CsPbBr₃/Si O₂/Au复合结构的双光子荧光增强及电场调控。我们设计并构建了CsPbBr₃/Si O₂/Au复合结构,并基于该复合结构实现了CsPbBr₃微米片双光子荧光增强,增强倍数可达～105.7倍。结合稳态和超快光谱测量,我们建立了相应的动力学模型,揭示了复合结构中双光子荧光增强主要起源于局域场增强效应、缺陷态填充效应以及更高的收集效率。进一步,通过在垂直于钙钛矿微米片平面的方向施加电场,我们研究了外加电场对CsPbBr₃微米片双光子荧光辐射的调控作用。结果表明,双光子荧光强度与外加电场的方向和大小有关,在外加电场作用下,我们实现了CsPbBr₃微米片双光子荧光增强倍数从～61.2倍至370.3倍的可控调节。电场调控的双光子荧光可归因于外加电场诱导微米片中Br空位的钝化和激活。另外,基于该复合结构我们还实现了电场对CsPbBr₃微米片双光子激光的动态开关效应,开关比可达67:1。（2）制备了二维层状Ruddlesden-Popper钙钛矿(BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）)单晶薄膜,研究了电场对二维钙钛矿单晶薄膜双光子荧光的调控。研究结果表明,电场对BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）单晶薄膜的双光子荧光强度也具有调控作用,但是荧光增强/减弱随电场极性的变化与无机钙钛矿CsPbBr₃相反。结合电压荧光光谱表征,我们发现电场对BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）荧光强度的调控来源于钙钛矿材料中电场对带负电缺陷俘获中心（主要为MA空位和I原子填隙）的钝化和激活。进一步,我们还发现电场对双光子荧光强度的调控幅度随着BA₂（MA）_n-1Pb_nI_3n+1钙钛矿无机层厚度（n）的增大而加强,在n=1时荧光强度的调控幅度为不加电场时强度的～92%至～114%,在n=2时调控幅度为～71%至～139%,在n=3时调控幅度进一步扩大为～33%至～201%。利用电场调控,我们实现了二维层状钙钛矿单晶薄膜双光子荧光的动态开关效应。（3）制备了钙钛矿（CsPbBr₃）单晶薄膜和单层过渡金属硫化物（WS₂）的异质结构,研究了电场对CsPbBr₃/WS₂异质结层间载流子输运的调控。研究结果表明,CsPbBr₃/WS₂异质结界面处CsPbBr₃和WS₂荧光强度均呈现出减弱的现象,说明形成的是II型异质结。在外加电场作用下,异质结处CsPbBr₃荧光强度的增强/减弱现象和电场的极性有关,当电场方向由CsPbBr₃指向WS₂时CsPbBr₃的荧光得到增强,当电场方向由WS₂指向CsPbBr₃时CsPbBr₃的荧光被减弱,说明通过调节电场极性可以分别实现对CsPbBr₃/WS₂异质结层间载流子输运的促进和抑制作用。更多还原

【Abstract】 Metal halide perovskite materials have shown great potential in the field of high-performance optoelectronic devices due to their excellent optoelectronic properties,such as high absorption coefficient,tunable optical bandgap,low defect density,high defect tolerance,and long carrier diffusion length.The ionic nature of lead halide perovskites makes them highly sensitive to external factors such as pressure,illumination,and temperature.In particular,the electric field provides a simple and effective mean to optimize and modulate the optoelectronic properties of perovskite materials,which is of great significance for enhancing the optoelectronic performance of perovskite materials and devices.The main contents of the paper are as follows:（1）We investigated the enhancement and electrical modulation of two-photon-absorption-induced photoluminescence（TPL）from CsPbBr₃/Si O₂/Au composite structure.First,we successfully prepared CsPbBr₃ microplate and then constructed the CsPbBr₃/Si O₂/Au hybrid structure by transferring CsPbBr₃ microplate to Si O₂-capped Au electrode arrays.A 105.7-fold enhancement of TPL from CsPbBr₃ microplate with hybrid the structure was realized.Based on steady-state and ultrafast spectral measurements,a kinetic model was established and revealed that the TPL enhancement of CsPbBr₃/Si O₂/Au structure originated from comprehensive effects including field localization effect,trap-filling effect,and increased collection efficiency.Furthermore,the electrical-modulated TPL emission from hybrid structure was explored,by applying an electric field along the direction perpendicular to the CsPbBr₃ microplate plane.The result indicated that TPL was related with the direction and amplitude of external electric field.Based on effect,we reached TPL enhancement from the structure ranging from～61.2-fold to 370.3-fold.The TPL enhancement/reduction of CsPbBr₃/Si O₂/Au structure was attributed to vertical-electric-field induced the passivation/activation effect of Br vacancies.In addition,we also achieved dynamic ON/OFF switching of two-photon lasing from CsPbBr₃/Si O₂/Au structure,with a switching ratio of 67:1.（2）We prepared BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal and then investigated the electrical modulation of TPL emission in BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal thin films.The TPL intensity of BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）single crystal thin films in the BA₂（MA）_n-1Pb_nI_3n+1/Si O₂/Au structure exhibited an opposite varying behavior,compared to that of CsPbBr₃ microplate with the structure.Through electric-field modulated fluorescence spectroscopy characterization techniques,we revealed that the TPL enhancement/reduction of BA₂（MA）_n-1Pb_nI_3n+1（n=1,2,3）was attributed to the passivation/activation of negatively charged trap centers（mainly MA vacancies and I interstitial）.As n-value increasing,the TPL tuning range monotonically increased.For BA₂Pb I₄（n=1）microflakes,the TPL intensity increased from～92%to～114%of the intensity at 0 V condition;for BA₂MAPb₂I₇（n=2）and BA₂（MA）₂Pb₃I₁₀（n=3）microflakes,the range was～71%to～139%and～33%to～201%,respectively.Based on the effect,we demonstrated a switchable ON/OFF effect of TPL emission in two-dimensional layered perovskite materials.（3）We studied the electrical-modulated carrier transport at the interface of the CsPbBr₃/WS₂ heterojunction.First,a composite structure of CsPbBr₃/WS₂/Si O₂/Au was constructed.Experimental results revealed a decrease in the fluorescence intensity for both CsPbBr₃ and WS₂ at the CsPbBr₃/WS₂ heterojunction interface,which indicating the formation of a type-II heterojunction.With applied voltage to Au electrode,the electrical-modulated fluorescence intensity of CsPbBr₃ at the heterojunction was found to be dependent on the polarity of the electric field.When the direction of electric field was from CsPbBr₃ to WS₂,the photoluminescence of CsPbBr₃ at the CsPbBr₃/WS₂ heterojunction increased,and when the direction of electric field was opposite,the photoluminescence of CsPbBr₃ at the CsPbBr₃/WS₂ heterojunction decreased,which indicating electric field could promote or suppress the carrier transport at the interface of the CsPbBr₃/WS₂ heterojunction.更多还原