Lim Vincent J-Y, Righetto Marcello, Yan Siyu, Patel Jay B, Siday Thomas, Putland Benjamin, McCall Kyle M, Sirtl Maximilian T, Kominko Yuliia, Peng Jiali, Lin Qianqian, Bein Thomas, Kovalenko Maksym, Snaith Henry J, Johnston Michael B, Herz Laura M
Department of Physics, Clarendon Laboratory, University of Oxford, Parks Road, Oxford OX1 3PU, United Kingdom.
Department of Physics, King's College London, London WC2R 2LS, United Kingdom.
ACS Energy Lett. 2024 Jul 29;9(8):4127-4135. doi: 10.1021/acsenergylett.4c01473. eCollection 2024 Aug 9.
Lattice dynamics are critical to photovoltaic material performance, governing dynamic disorder, hot-carrier cooling, charge-carrier recombination, and transport. Soft metal-halide perovskites exhibit particularly intriguing dynamics, with Raman spectra exhibiting an unusually broad low-frequency response whose origin is still much debated. Here, we utilize ultra-low frequency Raman and infrared terahertz time-domain spectroscopies to provide a systematic examination of the vibrational response for a wide range of metal-halide semiconductors: FAPbI, MAPbI Br , CsPbBr, PbI, CsAgBiBr, CuAgBiI, and AgI. We rule out extrinsic defects, octahedral tilting, cation lone pairs, and "liquid-like" Boson peaks as causes of the debated central Raman peak. Instead, we propose that the central Raman response results from an interplay of the significant broadening of Raman-active, low-energy phonon modes that are strongly amplified by a population component from Bose-Einstein statistics toward low frequency. These findings elucidate the complexities of light interactions with low-energy lattice vibrations in soft metal-halide semiconductors emerging for photovoltaic applications.
晶格动力学对光伏材料性能至关重要，它控制着动态无序、热载流子冷却、电荷载流子复合及输运。软金属卤化物钙钛矿展现出特别引人注目的动力学特性，其拉曼光谱呈现出异常宽泛的低频响应，但其起源仍备受争议。在此，我们利用超低频拉曼光谱和红外太赫兹时域光谱，对多种金属卤化物半导体：FAPbI、MAPbI₃、CsPbBr₃、PbI₂、CsAgBiBr₃、CuAgBiI₃和AgI的振动响应进行系统研究。我们排除了外在缺陷、八面体倾斜、阳离子孤对电子以及“类液体”玻色子峰作为有争议的中心拉曼峰的成因。相反，我们提出中心拉曼响应源于拉曼活性低能声子模式的显著展宽与玻色 - 爱因斯坦统计中向低频的粒子数分量强烈放大之间的相互作用。这些发现阐明了在用于光伏应用的软金属卤化物半导体中光与低能晶格振动相互作用的复杂性。
