Hu Yanzhuo, Liu Dong, Lu Ying-Bo, Wang Hao, Wu Zhongchen, Bao Hexin, Zou Ruijie, Jiang Xianyuan, Cong Wei-Yan, Guan Chengbo
Shandong Key Laboratory of Optical Astronomy and Solar-Terrestrial Environment, Institute of Space Sciences, Shandong University, Weihai 264209, China.
School of Space Science and Physics, Shandong University, Weihai 264209, China.
Phys Chem Chem Phys. 2024 Sep 11;26(35):22982-22989. doi: 10.1039/d4cp01681e.
The excitonic effect significantly influences the optoelectronic characteristics of halide perovskites. However, consensus on the temperature modulated exciton binding energy remains elusive, even for extensively studied materials like MAPbBr perovskites. In this study, we utilized UV-vis absorption spectra and the Elliott model to extract the exciton binding energies of MAPbBr in the range of 170-290 K. Elliott model fitted results reveal a linear increasing trend in bandgap and exciton binding energy for both cubic and tetragonal phases with temperature, with the tetragonal phase exhibiting a higher increasing rate. Additionally, we found that regardless of the temperature, the strongest absorption peaks are always dominated by the exciton absorption, and our fitted exciton absorption peak blue-shifts with the increase of temperature, accounting for the observed blue-shift of the strongest absorption peak for our fabricated MAPbBr sample. However, with the increase of temperature, the weight of continuum state absorption increases significantly, which widens the absorption tails to the longer wavelength, leading to the red-shift of Tauc-plotted optical bandgaps. This is the first work considering the temperature-modulated excitonic properties of halide perovskites, which offers valuable insights into the behavior of MAPbBr under varying temperature conditions. After a series of theoretical simulations on the temperature modulated electronic properties, including band structures, carrier effective masses, optical dielectric properties and Born effective charges, we provide rational interpretations for the experimentally observed temperature induced variation of the optical properties. These works are helpful to deepen our understanding of the temperature modulated optical properties of MAPbBr perovskites.
激子效应显著影响卤化物钙钛矿的光电特性。然而，即使对于像MAPbBr钙钛矿这样被广泛研究的材料，关于温度调制激子结合能的共识仍然难以达成。在本研究中，我们利用紫外可见吸收光谱和埃利奥特模型来提取170 - 290 K范围内MAPbBr的激子结合能。埃利奥特模型拟合结果表明，立方相和四方相的带隙和激子结合能均随温度呈线性增加趋势，其中四方相的增加速率更高。此外，我们发现无论温度如何，最强吸收峰始终由激子吸收主导，并且我们拟合的激子吸收峰随温度升高发生蓝移，这解释了我们制备的MAPbBr样品中最强吸收峰所观察到的蓝移现象。然而，随着温度升高，连续态吸收的权重显著增加，这使得吸收尾向更长波长扩展，导致Tauc图光学带隙发生红移。这是第一项考虑卤化物钙钛矿温度调制激子特性的工作，为MAPbBr在不同温度条件下的行为提供了有价值的见解。在对包括能带结构、载流子有效质量、光学介电性质和玻恩有效电荷等温度调制电子性质进行一系列理论模拟之后，我们对实验观察到的光学性质的温度诱导变化提供了合理的解释。这些工作有助于加深我们对MAPbBr钙钛矿温度调制光学性质的理解。
