For high-speed optoelectronic applications relying on fast relaxation or energy-transfer mechanisms, understanding of carrier relaxation and recombination dynamics is critical. Here, we compare the differences in photoexcited carrier dynamics in two-dimensional (2D) and quasi-three-dimensional (quasi-3D) colloidal methylammonium lead iodide perovskite nanoplatelets via differential transmission spectroscopy. We find that the cooling of excited electron-hole pairs by phonon emission progresses much faster and is intensity-independent in the 2D case. This is due to the low dielectric surrounding of the thin perovskite layers, for which the Fröhlich interaction is screened less efficiently leading to higher and less density-dependent carrier-phonon scattering rates. In addition, rapid dissipation of heat into the surrounding occurs due to the high surface-to-volume ratio. Furthermore, we observe a subpicosecond dissociation of resonantly excited 1s excitons in the quasi-3D case, an effect which is suppressed in the 2D nanoplatelets due to their large exciton binding energies. The results highlight the importance of the surrounding environment of the inorganic nanoplatelets on their relaxation dynamics. Moreover, this 2D material with relaxation times in the subpicosecond regime shows great potential for realizing devices such as photodetectors or all-optical switches operating at THz frequencies.

中文翻译：

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通过减少二维卤化物钙钛矿纳米片中的库仑筛选，加速了载体的松弛。

对于依赖快速弛豫或能量转移机制的高速光电应用，了解载流子弛豫和复合动力学至关重要。在这里，我们通过差分透射光谱比较了二维（2D）和准三维（准3D）胶态甲基铵碘化铅钙钛矿纳米片中光激发载流子动力学的差异。我们发现，通过声子发射来冷却激发的电子-空穴对的过程要快得多，并且在2D情况下与强度无关。这是由于钙钛矿薄层周围的介电常数较低，因此对Fröhlich相互作用的筛分效率较低，导致越来越依赖于密度的载流子-声子散射速率。此外，由于高的体积比，热量迅速散发到周围环境中。此外，在准3D情况下，我们观察到了共振激发的1s激子的亚皮秒解离，这种作用在2D纳米血小板中由于其大的激子结合能而受到抑制。结果突出了无机纳米片的周围环境对其松弛动力学的重要性。此外，这种亚材料具有亚皮秒级弛豫时间的2D材料对于实现诸如以THz频率运行的光电检测器或全光开关等设备显示出巨大的潜力。结果突出了无机纳米片的周围环境对其松弛动力学的重要性。此外，这种具有亚皮秒状态弛豫时间的2D材料对于实现诸如以THz频率运行的光电检测器或全光开关等设备显示出巨大的潜力。结果突出了无机纳米片的周围环境对其松弛动力学的重要性。此外，这种具有亚皮秒状态弛豫时间的2D材料对于实现诸如以THz频率运行的光电检测器或全光开关等设备显示出巨大的潜力。