研究机械应力对有机无机杂化钙钛矿中拉夏效应的影响

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"使用机械应力研究有机无机杂化钙钛矿中的拉什巴效应" 这篇研究论文探讨了在有机无机杂化钙钛矿（Organic-Inorganic Hybrid Perovskites）中利用机械应力来调查拉什巴效应（Rashba Effect）。拉什巴效应是由材料中的自旋-轨道耦合（Spin-Orbit Coupling, SOC）和结构反演不对称性共同引起的物理现象，对光发射和光伏性能有显著影响。在这种特殊的钙钛矿材料（例如MAPbI3-xClx）中，这两个特性同时存在，使得拉什巴效应的研究具有重要意义。研究人员提出了一种便捷的方法，通过机械弯曲（Mechanical Bending）来研究钙钛矿薄膜中的拉什巴效应。这种方法通过对单晶粒进行弹性变形，直接观察和分析其响应。实验中，他们注意到当应用凹面弯曲时，能导致薄膜的光谱线形展宽。这种线形展宽可能是由于机械应力改变了材料内部的电荷载流子动力学，进而影响了SOC和拉什巴效应的表现。此外，论文还可能深入讨论了以下几点： 1. **拉什巴效应的原理**：拉什巴效应是由于空间反演对称性的破坏导致的，这在没有这种对称性的材料中（如有机无机杂化钙钛矿）尤其明显。它会导致电子的有效质量在空间中依赖于自旋方向，从而影响电子的能带结构和光学性质。 2. **机械应力的作用**：通过施加机械应力，可以调控材料的局部应变状态，从而改变其电子结构和自旋态。弯曲导致的应变可能改变了材料的晶体结构，影响了SOC的强度和方向，进一步影响了拉什巴效应的大小和方向。 3. **实验技术与分析**：可能涉及高分辨率光谱技术（如光致发光光谱、吸收光谱等）用于检测线形变化，以及先进的显微技术（如扫描电子显微镜、原子力显微镜）用于观察和控制材料的微观形貌和应变状态。 4. **实际应用**：了解拉什巴效应对于优化钙钛矿太阳能电池和光电子设备的性能至关重要。通过控制拉什巴效应，可以潜在地提高器件的效率和稳定性，同时也可以为开发新型自旋电子器件提供理论基础。 5. **未来研究方向**：论文可能提出了未来研究如何利用机械应力精确调控拉什巴效应，以及在其他材料体系中探索类似现象的可能性。这篇研究论文对理解和利用有机无机杂化钙钛矿的拉什巴效应提供了新的视角，为优化这类材料的光电性能开辟了新的道路，并为自旋电子学领域带来了创新性的研究方法。

Using Mechanical Stress to Investigate the Rashba Eﬀect in

Organic−Inorganic Hybrid Perovskites

Haomiao Yu,

†

Qi Zhang,

†

Yaru Zhang,

†

Kai Lu,

‡

Changfeng Han,

†

Yijun Yang,

†

Kai Wang,

†

Xi Wang,

†

Miaosheng Wang,

Jia Zhang,

and Bin Hu*

,†,§

†

Key Laboratory of Luminescence and Optical Information, Ministry of Education, School of Science, Beijing Jiaotong University,

Beijing 100044, People’s Republic of China

‡

Wu Han National Laboratory for Optoelectronics, Huazhong University of Science and Technology, Wuhan, Hubei Province

430074, China

Department of Materials Science and Engineering, University of Tennessee, Knoxville, Tennessee 37996, United States

Supporting Information

ABSTRACT: Organic−inorganic hybrid perovskites simultaneously possess strong spin−

orbit coupling (SOC) and structure inversion asymmetry, establishing a Rashba eﬀect to

inﬂuence light emission and photovoltaics. Here, we use mechanical bending as a convenient

approach to investigate the Rashba eﬀect through SOC in perovskite (MAPbI

3−x

) ﬁlms

by elastically deforming grains. It is observed that applying a concave bending can broaden

the line shape of the magnetophotocurrent, increasing the internal magnetic parameter B

from 121 to 205 mT, which indicates an enhancement on SOC. Interestingly, the PL lifetime

is found to be enlarged from 9.9 to 14.8 ns under this bending, which suggests that

introducing compressive strain can essentially increase the Rashba eﬀect through SOC,

leading to an increase upon indirect band transition. Furthermore, the PL peak associated

with the Rashba eﬀect is shifted from 776 to 780 nm under this mechanical bending.

Therefore, mechanical bending provides a convenient experimental method to approach the

Rashba eﬀect in hybrid perovskites.

rganic−inorganic hybrid perovskites have demonstrated

attractive photovoltaic, light-emitting, lasing, and mag-

neto-optical properties, leading to interesting multifunctional

semiconducting materials.

1−7

Of these attractive properties, the

unique characteristics rely on the Rashba eﬀect caused by

spin− orbit coupling (SOC) under structural inversion

asymmetry.

8−17

Essentially, the Rashba eﬀect can be realized

in structural inversion asymmetry when the spin-up and spin-

down energies become nondegenerate in momentum space

under the inﬂuence of SOC. Within the framework of the

Rashba eﬀect, optical absorption is fully allowed due to spin

selection rules, yielding strong absorption coe ﬃcients.

However, upon optical absorption, an excited electron can

ﬂip its spin due to SOC and transition to an opposite spin-

band structure with spin-forbidden recombination, leading to

an enlarged lifetime. As a result, strong optical absorption and

a long carrier lifetime can concurrently occur,

providing a

precondition to generate remarkable photovoltaics. On the

other hand, electron−phonon coupling provides a mechanism

of breaking the spin-forbidden rec omb ination, activating

downward electronic transition toward light emission.

17−19

Therefore, the Rashba eﬀect plays an important role in

developing photovoltaic and light-emitting actions in organic−

inorganic hybrid perovskites. In this work, we mechanically

deformed the hybrid perovskite (MAPbI

3−x

) ﬁlm coated on

a ﬂexible PET substrate to morphologically vary the SOC by

introducing a vertically compressive stress by applying concave

bending. At the same time, we used photoluminescence (PL)

spectra to approach the Rashba eﬀect. The structural

deformation was characterized by X-ray diﬀraction (XRD)

measurements under compressive bending. The SOC was

monitored by magnetophotocurrent and polarization-depend-

ent photocurrent. Our studies show that applying a vertically

compressive stress can mainly increase the Rashba eﬀect by

introducing grain deformation and enhancing intrinsic SOC.

Consequently, the photoexcited states recombine through an

electron−phonon coupling mechanism with an enlarged

lifetime in organic−inorganic hybrid perovskites.

Here we applied mechanical bending onto a ﬂexible

perovskite device to introduce grain deformation on the

perovskite ﬁlm. The ﬂexible substrate was bent with a concave

shape, as illustrated in Figure 1a. This concave bending

generated two diﬀerent eﬀects: tensile stress laterally and

compressive stress vertically. As a result, the observed bending

eﬀects resulted from the combination of laterally tensile stress

and vertically compressive stress. To examine bending-induced

deformation in the perovskite ﬁlm, out-of-plane XRD measure-

ments on the sample of PET/MAPbI

3−x

were performed.

To make a clear comparison, we present the (110), (310), and

Received: July 8, 2019

Accepted: August 28, 2019

Published: August 28, 2019

Letter

pubs.acs.org/JPCL

Cite This: J. Phys. Chem. Lett. 2019, 10, 5446−5450

J. Phys. Chem. Lett. 2019, 10, 5446−5450

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研究机械应力对有机无机杂化钙钛矿中拉夏效应的影响

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