Department of Chemistry, University of Wisconsin-Madison , 1101 University Avenue, Madison, Wisconsin 53706, United States.
Department of Applied Physics, Nanjing University of Science and Technology , Nanjing, 210094, P. R. China.
Nano Lett. 2017 Jul 12;17(7):4405-4414. doi: 10.1021/acs.nanolett.7b01500. Epub 2017 Jun 13.
Metastable structural polymorphs can have superior properties and applications to their thermodynamically stable phases, but the rational synthesis of metastable phases is a challenge. Here, a new strategy for stabilizing metastable phases using surface functionalization is demonstrated using the example of formamidinium lead iodide (FAPbI) perovskite, which is metastable at room temperature (RT) but holds great promises in solar and light-emitting applications. We show that, through surface ligand functionalization during direct solution growth at RT, pure FAPbI in the cubic perovskite phase can be stabilized in nanostructures and thin films at RT without cation or anion alloying. Surface characterizations reveal that long-chain alkyl or aromatic ammonium (LA) cations bind to the surface of perovskite structure. Calculations show that such functionalization reduces the surface energy and plays a dominant role in stabilizing the metastable perovskite phase. Excellent photophysics and optically pumped lasing from the stabilized single-crystal FAPbI nanoplates with low thresholds were demonstrated. High-performance solar cells can be fabricated with such directly synthesized stabilized phase-pure FAPbI with a lower bandgap. Our results offer new insights on the surface chemistry of perovskite materials and provide a new strategy for stabilizing metastable perovskites and metastable polymorphs of solid materials in general.
亚稳结构的同素异形体具有比其热动力学稳定相更优越的性能和应用，但合理合成亚稳相是一个挑战。在这里，我们展示了一种使用表面功能化稳定亚稳相的新策略，以甲脒碘化铅（FAPbI）钙钛矿为例，其在室温下是亚稳的，但在太阳能和发光应用中具有很大的前景。我们表明，通过在室温下直接溶液生长过程中的表面配体功能化，可以在没有阳离子或阴离子合金化的情况下，在室温下稳定纳米结构和薄膜中的纯立方钙钛矿相 FAPbI。表面特性表明，长链烷基或芳基铵（LA）阳离子与钙钛矿结构的表面结合。计算表明，这种功能化降低了表面能，并在稳定亚稳钙钛矿相方面发挥了主导作用。从具有低阈值的稳定单晶 FAPbI 纳米板中演示了优异的光物理和光泵浦激光。可以用这种直接合成的稳定相纯 FAPbI 制造高性能太阳能电池，其带隙更低。我们的结果为钙钛矿材料的表面化学提供了新的见解，并为稳定亚稳钙钛矿和一般固体材料的亚稳同素异形体提供了一种新策略。
