Single Ensemble Non-exponential Photoluminescent Population Decays from a Broadband White-Light-Emitting Perovskite
Single Ensemble Non-exponential Photoluminescent Population Decays from a Broadband White-Light-Emitting Perovskite
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DOI：
10.1021/jacs.0c05636
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发表时间：
2020-09-30
影响因子：
15
通讯作者：
Fayer, Michael D.
中科院分区：
文献类型：
--
作者：
Thomaz, Joseph E.;Lindquist, Kurt P.;Fayer, Michael D.
紫外激发后层状Pb-X（X = Cl或Br）钙钛矿的白光发射机制引起了人们的极大兴趣。先前的时间依赖性研究表明，来自（110）钙钛矿的宽带光致发光（PL）产生于在具有不同衰减动力学的可见光谱的不同区域中发射的自陷激子位点的分布。本文利用时间相关单光子计数研究单晶，发现（110）钙钛矿（EDBE）PbBr_4（EDBE = 2，2 '-（亚乙二氧基）双（乙铵））的白光发射衰减表现为单一系综。在小光谱边带的快速衰减（0.6 ns）之后，宽发射线形状恒定为100 ns。我们认为，快速的局部结构波动导致自陷激子（STES）经历了很宽的能量范围，从而导致非常广泛的PL。与PL相比，STE在时间尺度上快速地对波动的局部环境进行采样，PL在所有发射波长处平均化PL衰减，从而产生单个系综PL动态。虽然发射发生从一个非常宽的，不均匀加宽的光谱线与时间平均单系综发光动力学，衰减是三指数。两个启发式模型的三指数衰减涉及缺陷进行了讨论。旋涂薄膜表现出更快的非指数衰减与晶体PL的最慢的组件缺席。像晶体一样，薄膜PL作为单个系综衰减。这些结果表明，（EDBE）PbBr 4的宽带发射衰减来自时间平均的单一系综，而不是从一组激发态发射不同的发光衰减在不同的波长。
The mechanism of white-light emission from layered Pb-X (X = Cl or Br) perovskites following UV excitation has generated considerable interest. Prior time-dependent studies indicated that the broadband photoluminescence (PL) from (110) perovskites arises from a distribution of self-trapped excitonic sites emitting in different regions of the visible spectrum with different decay dynamics. Here, using time-correlated single photon counting to study single crystals, we show that the white-light emission decay from the (110) perovskite (EDBE)PbBr4 (EDBE = 2,2 '-(ethylenedioxy)bis(ethylammonium)) behaves as a single ensemble. Following the rapid decay (0.6 ns) of a small spectral side band, the broad emission line shape is constant to 100 ns. We propose that rapid local structural fluctuations cause the self-trapped excitons (STEs) to experience a wide range of energies, resulting in the very broad PL. The STEs sample fluctuating local environments on time scales fast compared to the PL, which averages the PL decay at all emission wavelengths, yielding single ensemble PL dynamics. Although emission occurs from a very wide, inhomogeneously broadened spectral line with time-averaged single ensemble luminescence dynamics, the decay is tri-exponential. Two heuristic models for the tri-exponential decay involving defects are discussed. Spin-coated films show faster non-exponential decays with the slowest component of the crystal PL absent. Like the crystals, the film PL decays as a single ensemble. These results demonstrate that the broadband emission decay of (EDBE)PbBr4 arises from a time-averaged single ensemble and not from a set of excited states emitting with distinct luminescence decays at different wavelengths.