Division of Materials Science and Engineering, Ames Laboratory, Iowa State University, Ames, Iowa 50011, USA.
Department of Physics and Astronomy, Iowa State University, Ames, Iowa 50011, USA.
Nat Commun. 2017 Jun 1;8:15565. doi: 10.1038/ncomms15565.
How photoexcitations evolve into Coulomb-bound electron and hole pairs, called excitons, and unbound charge carriers is a key cross-cutting issue in photovoltaics and optoelectronics. Until now, the initial quantum dynamics following photoexcitation remains elusive in the hybrid perovskite system. Here we reveal excitonic Rydberg states with distinct formation pathways by observing the multiple resonant, internal quantum transitions using ultrafast terahertz quasi-particle transport. Nonequilibrium emergent states evolve with a complex co-existence of excitons, carriers and phonons, where a delayed buildup of excitons under on- and off-resonant pumping conditions allows us to distinguish between the loss of electronic coherence and hot state cooling processes. The nearly ∼1 ps dephasing time, efficient electron scattering with discrete terahertz phonons and intermediate binding energy of ∼13.5 meV in perovskites are distinct from conventional photovoltaic semiconductors. In addition to providing implications for coherent energy conversion, these are potentially relevant to the development of light-harvesting and electron-transport devices.
光激发如何演变成被称为激子的库仑束缚电子和空穴对，以及非束缚电荷载流子，这是光伏和光电领域的一个关键交叉问题。到目前为止，在混合钙钛矿体系中，光激发后的初始量子动力学仍然难以捉摸。在这里，我们通过观察超快太赫兹准粒子输运中的多个共振内部量子跃迁，揭示了具有不同形成途径的激子里德堡态。非平衡涌现态与激子、载流子和声子的复杂共存共同演化，在共振和非共振泵浦条件下，激子的延迟建立允许我们区分电子相干性的损失和热态冷却过程。在钙钛矿中，近 1ps 的退相时间、与离散太赫兹声子的有效电子散射以及 13.5meV 的中间结合能，都与传统的光伏半导体不同。除了对相干能量转换有影响外，这些发现还可能与光捕获和电子输运器件的发展有关。
