【作者】 何婷；

【导师】 徐法强；

【作者基本信息】 中国科学技术大学 ， 材料科学与工程， 2021， 硕士

【摘要】 近年来,铅基卤化物钙钛矿APbX3(其中A是有机或无机阳离子,X是卤素)由于其显著的光电性能而受到越来越多的关注。但是,铅和铅化合物的毒性严重限制了铅基卤化物钙钛矿的商业应用,因此用其它元素取代铅制备新型的非铅钙钛矿光电材料势在必行。研究表明,用同主族的锡元素来取代铅可以达到既能降低毒性问题又能较好地保持住钙钛矿的光电性能的目的。但到目前为止,还鲜有通过一步化学气相沉积法在硅基底上制备高质量的锡基卤化物钙钛矿晶体,并进行光电器件的制作和应用的报道。另外,锡基卤化物钙钛矿也有不稳定的缺点,其原因目前尚不确定,而且钙钛矿的光致发光机制仍然存在争议,这些问题的解决都需要对锡基钙钛矿进行系统的研究。本论文旨在:(1)探究化学气相沉积法中的工艺参数对CsSnBr3微晶的影响;(2)探究锡基钙钛矿的失效机制;(3)探究不同形貌的CsSnBr3微晶单体的光致发光性能,并研究发光机制。取得的主要结果如下:首先,我们在管式炉中利用一步化学气相沉积法,探究了沉积温度、沉积时间和载气压强等关键参数对CsSnBr3微晶的形貌和结构的影响。结果表明,沉积温度影响晶体的成核密度、形貌和结晶性,220℃时得到的微晶具有较好的均匀性和结晶度;沉积时间影响晶体的数量和大小,15min时得到的微晶尺寸较大且彼此之间不出现联结;载气压强几乎不影响晶体的沉积密度和大小,但对晶体的形状有明显影响,不同的压强下可以分别得到三角星状、钉子状、粗棒状和细针状的CsSnBr3微晶。随后,将CsSnBr3微晶避光放置在空气中探究其稳定性。实验发现在12小时后就出现了 SnO的X射线衍射峰且100小时后未观察到明显变化,而在100小时内没有明显观测到Sn4+,表明O容易取代CsSnBr3中的Br-形成SnO,因此锡基钙钛矿的不稳定性主要源于SnO的生成,而不是Sn2+的深度氧化。最后,分别对三角星状和钉子状CsSnBr3微晶单体都进行了稳态、变功率及变温光致发光测试。结果发现,与三角星状微晶相比,钉子状微晶发射峰的能量较高,表明钉子状微晶单体的发光存在量子效应。两种形貌的微晶单体的发光来源有所差别,主要是因为其激子结合能相差较大,三角星状具有较低的激子结合能13.5meV,因此它的发光来源可能是自由载流子和Sn空位诱导陷阱,而钉子状的激子结合能较大37.0meV,故其光激发物种是自由或束缚激子。此外,随着温度升高,晶格热膨胀和电子-声子的散射作用导致CsSnBr3微晶单体的发光峰的位置发生移动,晶格的无序、缺陷及声子的作用使得发光峰出现展宽效应。更多还原

【Abstract】 In recent years,lead halide perovskite APbX3(where A is an organic or inorganic cation,X is a halogen)have captured more attention because of their remarkable characteristics.However,the high toxicity of lead and lead compounds severely limits the commercial application of Pb-based halide perovskite.Therefore,it is imperative to replace lead with other elements to prepare new lead-free perovskite photoelectric materials.The substitution of lead by the tin element of the same group could reduce the toxicity and maintain the photoelectric properties of perovskite.Until now,however,there are few reports on the fabrication and application of high quality tin perovskite crystals on silicon substrate by one-step chemical vapor deposition.Sn-based perovskite also has a striking disadvantage,namely its instability,and the reason is still uncertain at present.In addition,there is still controversy about the species produced by perovskite after photoexcitation.The solution of these problems requires systematic research on Sn-based perovskite.Therefore,this thesis aims to:(1)explore the influence of key parameters in chemical vapor deposition on CsSnBr3 microcrystals;(2)explore the instability mechanism of tin-based perovskite;(3)investigate the photoluminescence properties of individual CsSnBr3 microcrystal with different morphologies and study the luminescence mechanism,The main findings are as follows:Firstly,we have studied the effects of key parameters such as deposition temperature,deposition time,and carrier gas pressure on the morphology and structure of CsSnBr3 microcrystals in a tube furnace via one-step chemical vapor deposition method.The results show that the deposition temperature affects the nucleation density,morphology and crystallinity of the crystals.The microcrystals obtained at 220℃ have better uniformity and crystallinity.The deposition time affects the number and size of the microcrystals,and the microcrystals obtained at 15 min are larger in size and there is no connection between each other.The carrier gas pressure hardly affects the deposition density and size of the microcrystals,but it has a significant influence on the shape of the microcrystals,and the microcrystals with the shape of triangle star,nail-like rod,thick rod and fine needle have been respectively obtained under different carrier gas pressure.Next,we attempted to illuminate the instability mechanism of CsSnBr3 microcrystals by placing the products in the air and away from light.The experiment found that the X-ray diffraction peak of SnO appeared after 12 hours and no other changes were observed after 100 hours.While the change of oxidation state of Sn2+was not clearly observed even after 100 hours,indicating that the stability of Sn-based perovskite comes from the formation of SnO,not the further oxidation of Sn2+.Finally,the steady state,power and temperature dependent photoluminescence spectroscopy were carried out on individual CsSnBr3 triangle star and nail-like rod.It is found that the emission energy of the nail-like is higher than that of the triangle star,indicating a quantum confinement effect in the nail-like rod.The luminescence nature of microcrystals with different morphologies are different,mainly due to the large difference in their exciton binding energy.The CsSnBr3 triangle star has a lower exciton binding energy(13.5 meV),so its luminescence source may be free carriers and Sn vacancies induced traps.As for the CsSnBr3 nail-like rod,the relatively large exciton binding energy(37.0 meV)leads to the photoluminescence mainly originating from free or bound exciton emission.In addition,as the temperature rises,the position of the luminescence peak of the CsSnBr3 microcrystals shifts due to the thermal expansion of the lattice and the electron-phonon scattering.The disorder,defects and phonons of the crystal lattice make the luminous peak appear broadening.更多还原