Dolan Connor J, Torma Andrew J, Sidhik Siraj, Mandani Faiz, Zhang Hao, Metcalf Isaac, Palmer Jack R, Deng Zhewen J D, Zhou Tao, Cai Zhonghou, Holt Martin V, Luo Yanqi, Lai Barry, Even Jacky, Fenning David P, Mohite Aditya D
Aiiso Yufeng Li Family Department of Chemical and Nano Engineering, University of California, San Diego, La Jolla, California 92093, United States.
Applied Physics Program, Smalley-Curl Institute, Rice University, Houston, Texas 77005, United States.
ACS Nano. 2025 Apr 8;19(13):13084-13096. doi: 10.1021/acsnano.4c18372. Epub 2025 Mar 27.
The halide perovskite formamidinium lead iodide (FAPbI) is a prime candidate for photovoltaics due to its excellent optoelectronic properties, but its application has been limited due to its structural instability. The large size of the FA cation results in metastability of the photoactive cubic phase and a facile degradation into thermodynamically stable hexagonal phases at room temperature. Recently, the incorporation of two-dimensional (2D) Ruddlesden-Popper halide perovskite seeds into a FAPbI precursor solution was shown to template the growth of and stabilize cubic FAPbI. Here, we investigate the nanoscale structural and optoelectronic mechanisms behind the observed bulk stabilization using synchrotron-based X-ray microscopies. Nanoprobe X-ray diffraction reveals 2D-templated FAPbI films exhibit an average compressive strain normal to the substrate of -3.3%, 2-fold larger than that of MACl-stabilized FAPbI. This compression creates locally templated regions composed of tetragonal-phase FAPbI distributed nonuniformly throughout the film with fewer crystalline defects than purely cubic regions. Scanning X-ray excited optical luminescence (X-ray analog of photoluminescence) reveals that this local templating results in increased radiative recombination and red-shifted band edge and emission. Our results provide insight into the microscopic mechanism for the phase stabilization of FAPbI using 2D perovskites as templates.
卤化物钙钛矿甲脒碘化铅（FAPbI）因其优异的光电性能而成为光伏领域的主要候选材料，但其应用因结构不稳定而受到限制。FA阳离子的大尺寸导致光活性立方相的亚稳性，并且在室温下容易降解为热力学稳定的六方相。最近，将二维（2D）Ruddlesden-Popper卤化物钙钛矿晶种掺入FAPbI前驱体溶液中被证明可以引导立方相FAPbI的生长并使其稳定。在此，我们使用基于同步加速器的X射线显微镜研究了所观察到的整体稳定性背后的纳米级结构和光电机制。纳米探针X射线衍射表明，二维模板化的FAPbI薄膜在垂直于衬底方向上表现出平均-3.3%的压缩应变，比MACl稳定的FAPbI大2倍。这种压缩产生了由四方相FAPbI组成的局部模板化区域，这些区域在整个薄膜中分布不均匀，且晶体缺陷比纯立方区域少。扫描X射线激发光致发光（光致发光的X射线类似物）表明，这种局部模板化导致辐射复合增加，带边和发射红移。我们的结果为使用二维钙钛矿作为模板对FAPbI进行相稳定的微观机制提供了见解。
