Wright Adam D, Buizza Leonardo R V, Savill Kimberley J, Longo Giulia, Snaith Henry J, Johnston Michael B, Herz Laura M
Department of Physics, University of Oxford, Clarendon Laboratory, Parks Road, Oxford OX1 3PU, United Kingdom.
TUM Institute for Advanced Study, Lichtenbergstraße 2a, 85748 Garching bei München, Germany.
J Phys Chem Lett. 2021 Apr 8;12(13):3352-3360. doi: 10.1021/acs.jpclett.1c00653. Epub 2021 Mar 30.
CsAgBiBr is a promising metal halide double perovskite offering the possibility of efficient photovoltaic devices based on lead-free materials. Here, we report on the evolution of photoexcited charge carriers in CsAgBiBr using a combination of temperature-dependent photoluminescence, absorption and optical pump-terahertz probe spectroscopy. We observe rapid decays in terahertz photoconductivity transients that reveal an ultrafast, barrier-free localization of free carriers on the time scale of 1.0 ps to an intrinsic small polaronic state. While the initially photogenerated delocalized charge carriers show bandlike transport, the self-trapped, small polaronic state exhibits temperature-activated mobilities, allowing the mobilities of both to still exceed 1 cm V s at room temperature. Self-trapped charge carriers subsequently diffuse to color centers, causing broad emission that is strongly red-shifted from a direct band edge whose band gap and associated exciton binding energy shrink with increasing temperature in a correlated manner. Overall, our observations suggest that strong electron-phonon coupling in this material induces rapid charge-carrier localization.
CsAgBiBr是一种很有前景的金属卤化物双钙钛矿，为基于无铅材料的高效光伏器件提供了可能性。在此，我们结合温度相关的光致发光、吸收光谱和光泵浦-太赫兹探测光谱，报道了CsAgBiBr中光激发电荷载流子的演化。我们观察到太赫兹光电导率瞬态的快速衰减，这揭示了自由载流子在1.0皮秒时间尺度上超快、无障碍地局域到本征小极化子态。虽然最初光生的离域电荷载流子表现出带状传输，但自陷小极化子态表现出温度激活迁移率，使得两者在室温下的迁移率仍超过1厘米²伏⁻¹秒⁻¹。自陷电荷载流子随后扩散到色心，导致从直接带边强烈红移的宽带发射，其带隙和相关的激子结合能随温度升高以相关方式缩小。总体而言，我们的观察结果表明，这种材料中强烈的电子-声子耦合会导致快速的电荷载流子局域化。
