LEAPS-MPS: Time- and depth-resolved charge carrier transport in phase stable hybrid perovskites

混合卤化物钙钛矿是一类新型的有机和无机混合半导体材料。它们在太阳能电池和发光二极管中显示出巨大的应用前景，部分原因是它们具有高度可调的电子和光学特性。然而，根本性的限制限制了它们的使用。特别是，由于离子迁移和相分离引起的稳定性问题必须得到解决。使钙钛矿研究复杂化的是电子过程的动态时间尺度。这些过程从皮秒电子散射、纳秒能量弛豫到毫秒离子运动。这项LEAPS-MPS项目将使用对电子传导敏感的太赫兹波来寻找开发稳定的混合钙钛矿的途径。为了实现这一目标，PI将开发新的非接触式太赫兹表征技术，将探测窗口从皮秒增加到毫秒级。THz研究将被光致发光和X射线表征所补充，以研究电子、光学和结构特性之间的动态耦合。PI强调对下一代科学家的培训，本科生和研究生研究人员将参与该项目。此外，PI还领导为小学女孩举办的Girls in Science夏令营，团队由女性教职员工、高中和大学助教组成。通过代际指导，该项目有助于培训下一代科学家和教育家。技术总结最近有机-无机杂化钙钛矿的发展为高度可调材料打开了广泛的机会。然而，热力学驱动的卤化物在混合卤化物钙钛矿中的分凝改变了它们的光学和光电性质。离子运动也会影响固体中的材料属性，需要广泛的时间范围才能了解动态材料属性。这项LEAPS-MPS项目旨在开发深度和时间分辨的非接触表征技术，以研究卤化物离子在光浸泡时对电荷载流子传输的影响，并寻找开发相稳定的杂化钙钛矿的途径。为了实现这一目标，PI将开发新的光泵浦、太赫兹探测技术，使用具有电子定时的ns脉冲泵浦激光器，将测量时间窗口从2 ns延长到1 ms以上，以匹配载流子复合动力学并增加动态探测窗口。太赫兹研究将得到时间和空间分辨的光致发光和原位X射线散射图的补充，以提供与局部薄膜应力和成分的关联。最终，该项目将把皮秒载流子散射、纳秒复合和毫秒离子运动联系起来，以提供对光载体动力学的全面了解。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

NON-TECHNICAL SUMMARYMixed halide perovskites are a novel class of hybrid semiconductors with organic and inorganic components. They have shown great promise for use in solar cells and light-emitting diodes, in part due to their highly tunable electronic and optical properties. However, fundamental limitations have limited their use. In particular, stability issues due to ion migration and phase segregation must be resolved. Complicating studies of pervoskites is the dynamic time scale of electronic processes. These span from picosecond electron scattering, nanosecond energy relaxation, to millisecond ionic motion. This LEAPS-MPS project will use terahertz waves that are sensitive to electron conduction to find pathways to develop stable hybrid perovskites. To achieve this goal, the PI will develop new non-contact terahertz characterization techniques to increase the probing window from picosecond to millisecond time scales. THz studies will be complemented by photoluminescence and X-ray characterization to investigate the dynamic coupling among electronic, optical, and structural properties. The PI emphasizes training for next generation scientists, involving undergraduate and graduate student researchers will be involved in the project. In addition, the PI leads the Girls in Science Camp for elementary school girls, with a team of female faculty members, high school, and college teaching assistants. Through intergenerational mentoring, this project contributes to the training of next-generation scientists and educators.TECHNICAL SUMMARYRecent developments in organic-inorganic hybrid perovskites have opened a wide range of opportunities for highly tunable materials. However, thermodynamically driven halide segregation in mixed-halide perovskites changes their optical and optoelectronic properties. Ionic motion also impacts material properties occurring in a solid, requiring a broad range of time scales to understand dynamic material properties. This LEAPS-MPS project seeks to develop depth- and time-resolved, non-contact characterization techniques to study the impact on charge carrier transport by the movement of halide ions upon light soaking and to find pathways to develop phase-stable hybrid perovskites. To achieve this goal, the PI will develop new optical pump, terahertz probe techniques using a ns-pulsed pump laser with electronic timing to extend the measurement time-window from 2 ns to beyond 1 ms to match carrier recombination dynamics and increase the dynamic probing window. THz studies will be complemented by time- and spatially-resolved photoluminescence and in situ X-ray scattering mapping to provide correlations with the local film stress and composition. Ultimately, this project will link picosecond carrier scattering, nanosecond recombination, and millisecond ionic motion to provide a comprehensive understanding of photocarrier dynamics.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.