离子液体辅助制备高质量钙钛矿薄膜及其光伏性能研究

It is an important topic in the efficiency improvement of perovskite solar cells that preparing perovskite film with regular structure, well coverage, and high crystallinity. The fabrication of CH3NH3PbI3 perovskite film, based on “two-step” method, need undergo three stages including the preparation of PbI2 precursor film, interfacial chemical conversion, and grain growth. These stages are interrelated and synergetic. According to this feature, this project utilizes ionic liquid to weaken the van der Waals interaction between the PbI2 layers, and to introduce liquid microdomain for grain growth. So we proposed a method taking ionic liquid as a single additive to control three stages mentioned above, respectively, in order to obtain high-quality perovskite film. First, through combining theoretical simulation, as well as various structural, optical and electrical measurements, we can reveal the principle of interaction between ionic liquid and PbI2, and further research the mechanism of dynamic control by ionic liquid in the processes of interfacial chemical conversion and grain growth. Second, in the view of the molecular structure, physical characteristics, and adding conditions of ionic liquid, we will clarify the structure-activity relationship of ionic liquid in the regulation of perovskite quality. Thirdly, we will in-depth investigate the influence of ionic liquid on the photovoltaic properties and broad-time-scale (fs-ms) carrier-related processes of perovskite solar cell. Finally, a simple but effective method for high-quality perovskite film will be summed up, which could bring a scientific reference for application of perovskite in solar cells and other photoelectronic devices.

制备结构规整、覆盖度及结晶性优异的高质量钙钛矿薄膜是实现钙钛矿太阳能电池效率提升的重要课题。以“两步法”制备CH3NH3PbI3钙钛矿需经过前驱体PbI2薄膜制备、界面化学转化和晶粒生长阶段。这三个阶段相互关联，且协同起效。针对这一特性，本项目利用离子液体削弱PbI2层间范德华相互作用，并为结晶生长引入液相微区，提出以离子液体单一添加剂分别调控以上三个阶段，从而获得高质量钙钛矿薄膜的方法。首先，利用理论模拟及多种结构、光、电探测手段，揭示离子液体和PbI2的作用原理，及其对界面化学转化和晶粒生长的动力学调控机制。其次，阐明离子液体分子结构、特征物性、添加条件与钙钛矿薄膜质量间的关系。此外，研究离子液体对钙钛矿太阳能电池光伏性能及多时域（fs-ms）载流子相关过程的影响。最后，总结简单有效的高质量钙钛矿薄膜制备方案，为钙钛矿材料在太阳能电池及其他光电器件中的应用提供科学指导。

本项目聚焦应用于光伏器件的高质量光吸收层的可控制备，通过深入探究光吸收薄膜的结构规整度、覆盖度、结晶性、掺杂及缺陷状态的变化规律，以破解太阳能电池中光吸收、载流子输运和复合三者间难以平衡的问题。项目从材料制备、界面调控和器件工艺等多个角度展开研究。系统考察了包括钙钛矿和量子点在内的光吸收材料性质对多种添加剂材料（离子液体、乙酸盐、金属卤化物等）的依赖性；深入探究了三维异质结器件结构对光吸收层的影响，并针对其建立了可控的三维异质结光伏器件制备及优化方法；在此基础上进一步开展抗弯折、柔性三维异质结器件和柔性电极材料的研究工作。取得了如下重要结果：（1）利用离子液体单一添加剂分别调控“两步法”制备CH3NH3PbI3钙钛矿中前驱体PbI2薄膜制备、界面化学转化和晶粒生长三个阶段，从而获得高质量钙钛矿薄膜。证实离子液体可与甲铵基形成氢键弱相互作用，从而提升钙钛矿薄膜热稳定性。最终获得光电转换效率15.7%的钙钛矿太阳能电池。（2）利用乙酸盐和金属卤化物在量子点相转移过程中实现对其表面配体、表面缺陷和掺杂程度的共同优化，从而获得光电转换效率>10%，空气稳定性>6个月的无封装量子点太阳能电池。（3）针对三维异质结太阳能电池中结构缺陷较多的问题，我们通过模板法实现了三维ZnO电子传输层的结构可控调节，并利用简单的压力后处理方法增加光吸收层致密度，减少电子传输层/光吸收层界面结构缺陷。（4）首次获得了三维异质结构的柔性ZnO/PbS量子点太阳能电池，利用ZnO纳米线阵列的弯折应力释放作用大幅度提升PbS量子点太阳能电池的抗弯折性，使该柔性电池在160o弯折角度下机械弯折100次，功率转换效率仍能保持原来的93%。本项目研究结果对于深刻理解高质量光吸收层制备过程中的物理、化学原理具有重要的参考价值，为研发基于钙钛矿和量子点的光电器件提供了科学依据和技术基础。