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Identification of high-temperature exciton states and their phase-dependent trapping behaviour in lead halide perovskites†
Energy & Environmental Science ( IF 32.5 ) Pub Date : 2018-03-20 00:00:00 , DOI: 10.1039/c7ee03543h
Jiangjian Shi 1, 2, 2, 3, 4 , Huiyin Zhang 1, 2, 2, 3, 4 , Yiming Li 1, 2, 2, 3, 4 , Jacek J. Jasieniak 5, 6, 7, 8 , Yusheng Li 1, 2, 2, 3, 4 , Huijue Wu 1, 2, 2, 3, 4 , Yanhong Luo 1, 2, 2, 3, 4 , Dongmei Li 1, 2, 2, 3, 4 , Qingbo Meng 1, 2, 2, 3, 4
Affiliation  

While lead halide perovskites have rapidly emerged as lucrative material candidates for optoelectronic applications, the crucial energy states and charge-carrier nature of these systems are yet to be fully understood, resulting in ongoing debates on the fundamental optical and material characters. In this work we probe the band-edge and sub-gap energy states within polycrystalline and single crystal perovskites to better understand their photophysical origins. Through temperature-, excitation intensity- and time-dependent optical measurements, we reveal the existence of both free and bound exciton contributions to the optoelectronic properties across a wide temperature region up to 300 K. The low-energy absorption and multiple-peak emission phenomena, whose physics origins have been highly controversial before, are caused by these exciton states. Furthermore, the trapping and recombination dynamics of these excitons is shown to be strongly dependent on the structural phase of the perovskite. The orthorhombic phase exhibits an ultrafast exciton trapping and distinct trap emissions, while the tetragonal phase gives low monomolecular recombination velocity and capture cross-sections (∼10−18 cm2). Within the multiphonon transition scenario, this suppression in charge trapping is caused by the increase in the charge capture activation energy due to a reduction in electron–lattice interactions within the inorganic framework, which can reasonably interpret the unexpectedly long carrier lifetime in these material systems. These findings provide a clearer understanding of the origins of the photophysical properties of perovskite materials, and the discovery of a high-temperature-stable bound exciton would bring the excitonic feature to be a concern for the perovskite energy conversion and utilization applications.

中文翻译:

鉴定卤化钙钛矿中高温激子态及其依赖于相的俘获行为

尽管卤化钙钛矿已迅速成为光电应用中的有利材料候选物,但这些系统的关键能态和电荷载流子性质尚未得到充分理解,从而引发了有关基本光学和材料特性的争论。在这项工作中,我们探索了多晶和单晶钙钛矿中的能带和亚带隙能态,以更好地了解它们的光物理起源。通过与温度,激发强度和时间相关的光学测量,我们揭示了在高达300 K的宽温度范围内,自由和束缚激子对光电性能的贡献。低能量吸收和多峰发射现象这些激子态引起了科学家的物理学起源,以前引起了很大争议。此外,这些激子的俘获和重组动力学显示出强烈依赖于钙钛矿的结构相。正交相表现出超快的激子俘获和独特的俘获发射,而四方相给出的低单分子重组速度和捕获截面(〜10-18 cm 2)。在多声子跃迁情形中,这种电荷俘获的抑制是由于无机骨架内电子-晶格相互作用的减少而导致的电荷俘获活化能的增加所引起的,这可以合理地解释这些材料系统中出乎意料的长载流子寿命。这些发现为钙钛矿材料的光物理性质的起源提供了更清晰的理解,而高温稳定的束缚激子的发现将使激子特性成为钙钛矿能量转换和利用应用中需要关注的问题。
更新日期:2018-03-20
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