基于分子设计和叠层自组装的二维钙钛矿薄膜制备及太阳能电池研究

Three-dimensional organic–inorganic perovskites have emerged as one of the most promising thin-film solar cell materials owing to their remarkable photophysical properties. One of the critical factors that hinder their photovoltaic application is the poor environmental stability and photostability under operating conditions. In contrast, to their three-dimensional counterparts, layered two-dimensional (2D) perovskites, which have shown promising stability, exhibit low efficiency due to their wide bandgap, inhibited out-of plane charge transport, and poor film quality. In order to increase the efficiencies of two-dimensional perovskite solar cells, the design principle for 2D perovskite with desired properties, advanced film deposition techniques as well as optimized device architectures for 2D perovskite solar cells will be investigated. In pursuit of the desired layered perovskites with high stability, tunable bandgap and good carrier transport properties, the influence on electrical structure, electronic properties and chemical properties of layered perovskites by inorganic component structure variety, the size and status of organic component will be studied by the method of combining experimental research and quantum theoretical calculation; Uniform and pinhole-free (RNH3)2(MA)n-1PbnX3n+1 perovskite film with good photoelectrical properties will be fabricated using the novel layer-by-layer assembly and reaction technique, and the assembling dynamics and methods to control the microstructure of (RNH3)2(MA)n-1PbnX3n+1 thin films will be studied. 2D perovskite solar cells basing on these multilayered organic-inorganic hybrids will be designed and the interfaces between hybrid absorbing layer and carrier transporting layer will be optimized. Effect of composition, microstructure, electronic structure of the hybrid films as well as their interface contact and charge transporting and recombination dynamics will be analyzed in detail, with the aim of reaching or overpassing the present highest efficiency level.

三维有机-无机钙钛矿杂合物具有优异的光伏特性，但其环境稳定性和光学稳定性还需大幅提高。与之相反，二维有机-无机钙钛矿杂合物具有优异的稳定性，但性能理想的高质量多钙钛矿层二维杂合物薄膜却难以获得。为此，本项目提出采用独特的叠层自组装反应法生长多钙钛矿层杂合物(RNH3)2(MA)n-1PbnX3n+1薄膜，研究杂合物薄膜在分子尺度下的可控生长和微结构控制方法；结合实验研究和量子计算，系统研究无机层数目和组成、有机元种类和次级结构对杂合物结构和电子学性能的影响规律，设计并制备光电转换性能优异的高质量多钙钛矿层二维杂合物薄膜；构筑基于(RNH3)2(MA)n-1PbnX3n+1的钙钛矿太阳电池，系统考察各功能层的制备工艺、微结构、界面电荷注入特性等对电池光电转换效率和载流子传输性能的影响规律，探索实现高效率二维钙钛矿太阳能电池的途径。

新型有机-无机杂化二维钙钛矿具有优良的光电性能和稳定性，在太阳能电池领域引起广泛关注。本项目采用实验研究与量子理论计算和模拟仿真相结合方法，系统研究无机层数目和组成、有机元种类和次级结构对二维钙钛矿杂合物结构和电子学性能的影响规律，获得满足太阳能电池应用需求的杂合物设计原则和薄膜制备方法。首次采用两步法成功制备出致密、均一且结晶度高的准二维钙钛矿薄膜(PEA)2FAn-1PbnI3n+1和(C3H7NH3)2FAn-1PbnI3n+1，其相应钙钛矿太阳能电池的光电转换效率分别为11.46%和12.55%，不仅高于对应的三维FAPbI3电池，稳定性相比于FAPbI3电池也明显提高；采用原位自组装反应法制备(Br-PEA)2(MA)4Pb5I16薄膜，研究添加剂种类和含量对薄膜结构和性能的影响发现，添加剂中的MA+离子有利于促进高n值钙钛矿的形成和钙钛矿的垂直取向生长，而Ac-作为一种Lewis碱，能够与前驱体溶液中Pb2+和DMF相互络合形成中间相。添加10%wt MAAc时薄膜的结晶性和覆盖率较好，对光的吸收也最强，光电转换效率可达8.47%；采用热铸法制备(XPEA)2(MA)n-1PbnI3n+1（X=H，Cl，Br）薄膜，研究发现，有机间隔阳离子中取代基的电负性对薄膜的形貌、结晶度和取向、相分布和吸收性能有显著影响。以Cl-PEA和Br-PEA为A位有机组元制得的二维钙钛矿薄膜表面致密，结晶度高，载流子寿命长，其光电转换效率分别达11.86%和11.61%，电池的湿度稳定性优于MAPbI3；利用SCAPS软件，建立基于窄禁带Pb-Sn混合钙钛矿FA0.5MA0.5Pb0.5Sn0.5I3的p-i-n结构太阳能电池。仿真结果表明钙钛矿吸收层的内建电场和界面复合受各级界面的能级结构影响较大，经过仿真优化器件结构和材料参数，电池的开路电压由0.67V提高到 0.87V, 短路电流由28.75 mA/cm2 to 29.25 mA/cm2, 填充因子由76.66%提高到 80.78%, 电池的转换效率从14.79%增加到19.47%。