Lou Xue, Li Yahui, Lei Haixin, Zhang Yao, Zhou Hongzhi, Shi Enzheng, Zhu Haiming
State Key Laboratory of Extreme Photonics and Instrumentation, Department of Chemistry, Zhejiang University, Hangzhou, Zhejiang 310027, China.
Zhejiang University-Hangzhou Global Scientific and Technological Innovation Center, Hangzhou, Zhejiang 311200, China.
ACS Nano. 2024 Jul 23. doi: 10.1021/acsnano.4c06336.
Two-dimensional (2D) perovskites, comprising inorganic semiconductor layers separated by organic spacers, hold promise for light harvesting and optoelectronic applications. Exciton transport in these materials is pivotal for device performance, often necessitating deliberate alignment of the inorganic layers with respect to the contacting layers to facilitate exciton transport. While much attention has focused on in-plane exciton transport, little has been paid to out-of-plane interlayer transport, which presumably is sluggish and unfavorable. Herein, by time-resolved photoluminescence, we unveil surprisingly efficient out-of-plane exciton transport in 2D perovskites, with diffusion coefficients (up to ∼0.1 cm s) and lengths (∼100 nm) merely a few times smaller or comparable to their in-plane counterparts. We unambiguously confirm that the out-of-plane exciton diffusion coefficient corresponds to a subpicosecond interlayer exciton transfer, governed by the Förster resonance energy transfer (FRET) mechanism. Intriguingly, in contrast to temperature-sensitive intralayer band-like transport, the interlayer exciton transport exhibits negligible temperature dependence, implying a lowest-lying bright exciton state in 2D perovskites, irrespective of spacer molecules. The robust and ultrafast interlayer exciton transport alleviates the constraints on crystal orientation that are crucial for the design of 2D perovskite-based light harvesting and optoelectronic devices.
二维（2D）钙钛矿由被有机间隔层隔开的无机半导体层组成，在光捕获和光电器件应用方面具有潜力。这些材料中的激子传输对于器件性能至关重要，通常需要使无机层相对于接触层进行有意的排列，以促进激子传输。虽然很多注意力都集中在面内激子传输上，但对垂直于平面的层间传输关注较少，人们推测这种传输是缓慢且不利的。在此，通过时间分辨光致发光，我们揭示了二维钙钛矿中垂直于平面的激子传输效率惊人，其扩散系数（高达约0.1 cm²/s）和长度（约100 nm）仅比其面内对应值小几倍或与之相当。我们明确证实，垂直于平面的激子扩散系数对应于亚皮秒级的层间激子转移，这由福斯特共振能量转移（FRET）机制控制。有趣的是，与对温度敏感的层内带状传输不同，层间激子传输对温度的依赖性可忽略不计，这意味着二维钙钛矿中存在最低的明亮激子态，与间隔分子无关。这种稳健且超快的层间激子传输减轻了对晶体取向的限制，而晶体取向对于基于二维钙钛矿的光捕获和光电器件设计至关重要。
