【作者】 禹光辉；

【导师】 宋延林； 蒋克健；

【作者基本信息】 郑州大学 ， 有机化学， 2023， 博士

【摘要】 有机-无机杂化钙钛矿因为具有高吸光系数,长载流子扩散长度,可调节光学带隙,以及低成本等优势,被认为是制备下一代光伏电池的理想半导体材料,近年来受到了广泛的关注。经过十多年的发展,目前单结钙钛矿太阳能电池的光电转化效率已经达到25.7%。但是,由于有机-无机杂化钙钛矿中含有易挥发的有机成分,杂化钙钛矿热稳定性较差,可能阻碍其商业应用。用无机的铯离子代替杂化钙钛矿中的有机阳离子,制备全无机的铯基钙钛矿是提高钙钛矿稳定性的一个重要途径。无机钙钛矿（CsPb（I,Br）₃）中,铯铅碘（CsPbI₃）钙钛矿具有最小的带隙（约1.7 eV）,适合于制备单结和叠层太阳能电池。由于铯离子直径偏小,难以支撑铅碘八面体[PbI₆]^4-通过角共享形成的立方空间,在室温下,尤其是在高湿环境下,CsPbI₃易从钙钛矿转化为非钙钛矿相,失去光学活性。经过不断探索,研究人员发现,CsPbI₃钙钛矿相变过程通常从晶体界面和晶体缺陷位置开始。因而,改善钙钛矿的薄膜质量,有利于提高CsPbI₃钙钛矿电池的光电转化效率和稳定性。本论文主要通过以下三个方面来制备高质量的CsPbI₃钙钛矿薄膜,提高太阳能电池的光电转化效率和稳定性:（1）用聚丙烯腈（PAN）作为钝化剂钝化CsPbI₃钙钛矿膜的缺陷。PAN碳链骨架侧链上的氰基（-CN）可以通过氮（N）原子的孤对电子与钙钛矿晶体中带有正电荷的铅离子相互作用,从而降低钙钛矿的缺陷态密度,增加相变能垒,提升钙钛矿相的稳定性;另外,PAN可促进钙钛矿成核,制备平整和致密的钙钛矿晶体薄膜;而且,由于PAN的稳定作用,增强了钙钛矿薄膜在高湿环境下的稳定性。（2）CsPbI₃钙钛矿薄膜制备通常添加二甲胺氢碘酸盐（DMAI）,首先形成DMAPbI₃中间相,然后在退火过程中,通过离子交换反应,生成CsPbI₃钙钛矿薄膜,同时去除DMAI。我们采用真空辅助退火（VATA）方式,平衡了 DMAI的生成和分离速度,制备高质量钙钛矿薄膜。薄膜缺陷态密度明显减少,载流子扩散长度增长,太阳能电池效率得到明显增长。（3）基于DMAI添加剂辅助制备CsPbI₃钙钛矿太阳能电池的效率已经达到21%,但是由于低温制备方法（～200℃）,钙钛矿薄膜中可能残留DMAI,影响薄膜和器件的稳定性。为了得到全无机CsPbI₃钙钛矿,我们采用更易挥发的乙胺氢碘盐（EAI）代替DMAI,并通过提升退火温度以促进有机成分的挥发。前驱体溶液在旋涂后首先形成一维EAPbI₃薄膜,然后在340℃的高温下退火并通过EA⁺和Cs⁺的离子交换,形成三维的全无机CsPbI₃钙钛矿薄膜。通过1H核磁分析,红外光谱（FTIR）和X射线光电子能谱（XPS）等多种方式确认了最终薄膜的组成。采用该方式制备的CsPbI₃钙钛矿薄膜结晶性和取向性得到提高,薄膜形貌更加致密平整,晶体缺陷密度明显下降,制备的钙钛矿电池转化效率和稳定性都获得了显著提高。更多还原

【Abstract】 In recent years,the organic-inorganic hybrid perovskite material has attracted extensive attention due to its intrinsic outstanding photoelectric characteristics,including high absorption coefficient,long carrier diffusion length,adjustable and proper band gap,and low solution preparation cost.It has been considered as one of the most promising photovoltaic materials in next-generation solar cells.After more than ten years of development,the power conversion efficiency of the single-junction perovskite solar cells has reached to 25.7%,comparable to that of the commercial silicon solar cells.However,due to the presence of volatile organic components in the organic-inorganic hybrid perovskite materials,the film stability is reduced,limiting the long-term stability operation of the devices and probably hindering its commercial application.All-inorganic perovskites（CsPb（I,Br）₃）,replacing the organic cation with Cs⁺,would be an effective way to address the issue.Among them,cesium-lead-iodine（CsPbI₃） perovskite has the smallest band gap（about 1.7 eV）,suitable for the fabrication of single or multi-junction solar cells.However,due to the small diameter of cesium ion,CsPbI₃ perovskite is prone to convert to non-perovskite phase at room temperature,and lose its optical activity,especially in high humidity environment.With long-term exploration,researchers have found that the phase transition usually starts at the crystal interface and the crystal defect position.Therefore,it is necessary to improve the film quality to enhance both the efficiency and stability of the CsPbI₃ perovskite solar cells.In order to improve the photoelectric conversion efficiency and stability of CsPbI₃ perovskite solar cells,in this thesis,three approaches have been carried out to improve the CsPbI₃ film quality.（1）The polyacrylonitrile（PAN）,as a passivator,is used to decrease the defects of CsPbI₃ perovskite film.The cyano（-CN）on the side chain of the PAN can interact with the lead ion in the CsPbI₃ perovskite,reducing the density of defect states,increasing the phase transition energy barrier,and improving the film stability.In addition,the addition of PAN promotes the crystal nucleation for the formation of a flat and compact CsPbI₃ film.Moreover,the humidity stability of the film is enhanced due to the stabilizing effect of PAN.（2）Dimethylamine hydroiodate（DMAI）is usually employed as an additive for the preparation of high-efficiency CsPbI₃-based solar cells.DMAPbI₃ intermediate phase is first formed after the solution deposition,and then converted to CsPbI₃ perovskite phase through ion exchange reaction duing annealing,accompanying with the exhaust of gaseous DMAI produced.Herein,a vacuum-assisted thermal annealing（VATA） approach is used to balance the formation and separation of DMAI during the ion exchange reaction.The VATA approach promots the formation of high-quality CsPbI₃ perovskite films,reducing the density of defect states of the film,enhancing the carrier diffusion length,and thus improving the efficiency of the resulting solar cells.（3）PCE of the DMAI-assisted CsPbI₃ perovskite solar cells has reached to 21%,however,whether a certain amount of DMAI exists in the resulting film is controversial due to the relatively low annealing temperatures（～200℃）.For the fabrication of CsPbI₂ perovskite film,we used more volatile ethylammonium iodide（EAI）instead of DMAI,and significantly increased the annealing temperature（～340℃） to promote the volatilization of organic component,where one-dimensional EAPbI₃ was first formed,and then converted into three-dimensional CsPbI₃ perovskite through ion exchange reaction between EA and Cs cations during the annealing.The composition of the CsPbI₃ perovskite was verified by ¹H nuclear magnetic resonance analysis（¹H-NMR）,infrared spectroscopy（FTIR）,and X-ray photoelectron spectroscopy（XPS）.By the strategy,a compact and flat CsPbI₃ film was formed with high crystallinity and orientation.The density of the defect status of the film decreased significantly,and the photoelectric conversion efficiency and stability of the solar cell were significantly improved.更多还原