Liu Diwen, Li Qiaohong, Jing Huijuan, Wu Kechen
State Key Laboratory of Structural Chemistry, Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences Fuzhou 350002 P. R. China
University of Chinese Academy of Sciences Beijing 100049 P. R. China.
RSC Adv. 2019 Jan 24;9(6):3279-3284. doi: 10.1039/c8ra10251a. eCollection 2019 Jan 22.
Perovskite photovoltaic materials are gaining significant attention due to their excellent photovoltaic properties. In this study, density functional theory calculations were performed to investigate the structure and electronic and optical properties of CsGeI under hydrostatic strain. The results show that the band gap of CsGeI can be tuned from 0.73 eV to 2.30 eV under different strain conditions. The results indicate that the change in the band gap under strain is likely to be determined by the Ge-I-Ge bond angle. Interestingly, the length of the short Ge-I bond remains unchanged, whereas that of the long Ge-I bond exhibits an evident increment with strain ranging from -4% to 4%. A suitable band gap (1.36 eV) of CsGeI can be obtained under a strain of -1%. Both the calculated elastic constants and the phonon spectrum imply that this structure is stable under the abovementioned condition. Bandgap narrowing induces a red shift of the light absorption spectrum of CsGeI by extending the onset light absorption edge. These results are important for understanding the effects of strain on the halide perovskites and guiding the experiments to improve the photovoltaic performance of the perovskite solar cells.
钙钛矿光伏材料因其优异的光伏性能而备受关注。在本研究中，进行了密度泛函理论计算，以研究静水压力应变下CsGeI的结构、电子和光学性质。结果表明，在不同应变条件下，CsGeI的带隙可从0.73 eV调谐至2.30 eV。结果表明，应变下带隙的变化可能由Ge-I-Ge键角决定。有趣的是，短Ge-I键的长度保持不变，而长Ge-I键的长度在-4%至4%的应变范围内呈现明显增加。在-1%的应变下可获得合适的CsGeI带隙（1.36 eV）。计算得到的弹性常数和声子谱均表明该结构在上述条件下是稳定的。带隙变窄通过扩展起始光吸收边缘导致CsGeI光吸收光谱发生红移。这些结果对于理解应变对卤化物钙钛矿的影响以及指导实验提高钙钛矿太阳能电池的光伏性能具有重要意义。
