Straus Daniel B, Hurtado Parra Sebastian, Iotov Natasha, Zhao Qinghua, Gau Michael R, Carroll Patrick J, Kikkawa James M, Kagan Cherie R
Department of Chemistry, University of Pennsylvania, Philadelphia, Pennsylvania 19130, United States.
Department of Physics, University of Pennsylvania, Philadelphia, Pennsylvania 19130, United States.
ACS Nano. 2020 Mar 24;14(3):3621-3629. doi: 10.1021/acsnano.0c00037. Epub 2020 Mar 5.
We report a family of two-dimensional hybrid perovskites (2DHPs) based on phenethylammonium lead iodide ((PEA)PbI) that show complex structure in their low-temperature excitonic absorption and photoluminescence (PL) spectra as well as hot exciton PL. We replace the 2-position () H on the phenyl group of the PEA cation with F, Cl, or Br to systematically increase the cation's cross-sectional area and mass and study changes in the excitonic structure. These single atom substitutions substantially change the observable number of and spacing between discrete resonances in the excitonic absorption and PL spectra and drastically increase the amount of hot exciton PL that violates Kasha's rule by over an order of magnitude. To fit the progressively larger cations, the inorganic framework distorts and is strained, reducing the Pb-I-Pb bond angles and increasing the 2DHP band gap. Correlation between the 2DHP structure and steady-state and time-resolved spectra suggests the complex structure of resonances arises from one or two manifolds of states, depending on the 2DHP Pb-I-Pb bond angle (as)symmetry, and the resonances within a manifold are regularly spaced with an energy separation that decreases as the mass of the cation increases. The uniform separation between resonances and the dynamics that show excitons can only relax to the next-lowest state are consistent with a vibronic progression caused by a vibrational mode on the cation. These results demonstrate that simple changes to the cation can be used to tailor the properties and dynamics of the confined excitons without directly modifying the inorganic framework.
我们报道了一族基于苯乙铵碘化铅（(PEA)PbI）的二维杂化钙钛矿（2DHPs），它们在低温激子吸收和光致发光（PL）光谱以及热激子PL中表现出复杂的结构。我们用F、Cl或Br取代PEA阳离子苯基上的2位氢，以系统地增加阳离子的横截面积和质量，并研究激子结构的变化。这些单原子取代显著改变了激子吸收和PL光谱中离散共振的可观测数量和间距，并使违反卡沙规则的热激子PL量急剧增加了一个数量级以上。为了容纳逐渐增大的阳离子，无机骨架发生扭曲和应变，减小了Pb-I-Pb键角并增加了2DHP带隙。2DHP结构与稳态和时间分辨光谱之间的相关性表明，共振的复杂结构源于一或两个状态流形，这取决于2DHP的Pb-I-Pb键角（非）对称性，并且一个流形内的共振以规则间隔排列，能量间隔随着阳离子质量的增加而减小。共振之间的均匀间隔以及激子只能弛豫到次低能态的动力学过程与阳离子上的振动模式引起的电子振动跃迁相一致。这些结果表明，对阳离子进行简单改变可用于定制受限激子的性质和动力学，而无需直接修改无机骨架。
