柔性钙钛矿光电器件中的关键科学问题研究：应力对钙钛矿体内光电过程的影响

Perovskites exhibit considerable application prospects in photovoltaic, luminescent and laser fields due to its unique semiconductor characteristics, electric polarization and spin-orbital coupling characteristics. The rapid development of flexible perovskite photovoltaic and light-emitting devices provides new possibilities for the field of flexible electronics. Strain is an inevitable process in bending and stretching of flexible perovskite films. Especially, strain can affect the photoelectric process by changing the semiconductor properties, polarization and spin-orbital coupling of perovskite films. Therefore, the effect of strain on the photoelectric process has become a key scientific issue in the research of flexible perovskite thin film devices. Based on our previous important research progress, this project will reveal the important effects of compression and tensile strain in perovskite films on orbital polarization, spin-orbital coupling and Rashba effect by using our effective experimental methods: magnetic field effects, circular photoexcitation modulated photocurrents, characterization of steady-state and dynamic excitation state behaviors, and by introducing convex and concave flexible bending. The research goal is to reveal the underlying mechanisms to tune photoelectric process by flexible bending in perovskite films which plays a solid scientific foundation for the performance improvement of flexible perovskite photovoltaic and light-emitting devices, also for the development and application of perovskite in flexible electronics.

钙钛矿因其独特的半导体特性、电极化、自旋轨道耦合特性在光伏、发光、激光领域展现出可观的应用前景，柔性钙钛矿光伏、发光器件的快速发展更是为柔性电子领域提供了新的可能。应力是柔性钙钛矿薄膜在弯曲和拉伸中所产生的必然过程，尤其是应力可以通过改变钙钛矿的半导体特性、电极化、自旋轨道耦合从而影响其光电过程，因此，应力对光电过程的影响成为柔性钙钛矿薄膜器件研究中的关键科学问题。本项目将根据我们前期重要研究进展，利用我们有效实验手段：激发态磁光效应、偏振光诱导光电效应、稳态及动态激发态行为表征，通过引入凸、凹柔性弯曲，揭示钙钛矿薄膜体内压缩、拉伸应力对轨道极化、自旋轨道耦合、Rashba效应的重要影响，在此基础上阐明柔性弯曲对钙钛矿薄膜中光电过程调控的基本机理，为提高柔性钙钛矿光伏、发光器件性能，为钙钛矿在柔性电子学的发展及应用打下坚实的科学基础。

得益于金属卤化物钙钛矿薄膜优异的光电性能和可低温溶液加工的特点，柔性钙钛矿光电器件在光伏、发光及探测领域均展现出巨大的应用前景。应力是柔性钙钛矿薄膜在弯曲和拉伸中所产生的必然过程，尤其是应力可以通过改变钙钛矿的半导体特性、电极化、自旋轨道耦合从而影响其光电过程，因此，应力对光电过程的影响成为柔性钙钛矿薄膜光电器件研究中的关键科学问题。本项目中，我们针对应力对钙钛矿薄膜缺陷、电极化、自旋轨道耦合作用及电荷输运的影响及其作用机制展开深入研究，实验发现增加钙钛矿薄膜面内压缩应力会降低缺陷态密度，提高电极化强度和自旋轨道耦合作用，同时对于电荷输运的影响较小；增加薄膜面内拉伸应力则会产生相反的作用效果。进一步研究表明，应力作用下的缺陷态密度降低与晶界间相互作用及缺陷形成能有关，电极化和自旋轨道耦合作用增强则与轨道间相互作用直接相关。在此基础上，我们利用机械弯曲的方式，成功实现了柔性钙钛矿太阳能电池器件短路电流从初始的15.39 mA/cm2提升至22.00 mA/cm2，增幅达到43%，同时器件的开路电压及填充因子几乎没有变化，最终器件能量转换效率从最初的9.4%上升至12.95%。本项目的研究成果充分表明应力工程可以有效地调控钙钛矿光电性质，对于柔性钙钛矿光电器件是一种新的调控机制，并为通过机械应力来控制金属卤化物钙钛矿的光电性能带来了巨大的机遇。