Yan Hejin, Li Yingfeng, Li Xiang, Wang Bingxin, Li Meicheng
State Key Laboratory of Alternate Electrical Power System with Renewable Energy Sources, North China Electric Power University Beijing China 102206
RSC Adv. 2020 Jan 3;10(2):958-964. doi: 10.1039/c9ra06731k. eCollection 2020 Jan 2.
CsTiI Br is a potential light absorption material for all-inorganic lead free perovskite solar cells due to its suitable and tunable bandgap, high optical absorption coefficient and high environmental stability. However, solar cells fabricated based on CsTiI Br do not perform well, and the reasons for their low efficiency are still unclear. Herein, hot carrier relaxation processes in CsTiI Br ( = 0, 2 and 6) were investigated by a time-domain density functional theory combined with the non-adiabatic molecular dynamics method. It was found that the relaxation time of the hot carriers in CsTiI Br ranges from 2-3 ps, which indicates that the hot carriers within 10 nm from the CsTiI Br /TiO interface can be effectively extracted before their energy is lost completely. The carrier-phonon non-adiabatic coupling (NAC) analyses demonstrate that the longer hot electron relaxation time in CsTiIBr compared with that in CsTiBr and CsTiI originates from its weaker NAC strength. Furthermore, the electron-phonon interaction analyses indicate that the relaxation of hot electrons mainly comes from the coupling between the electrons distributed on the Ti-X bonds and the Ti-X vibrations, and that of hot holes can be attributed to the coupling between the electrons distributed on the X atoms and the distortions of [TiI Br ]. The simulation results indicate that CsTiIBr should be better than CsTiBr and CsTiI to act as a light absorption layer based on the hot carrier energy loss, and the hot electron relaxation time in CsTiI Br can be adjusted by tuning the proportion of the I element.
CsTiI₂Br因其合适且可调节的带隙、高光学吸收系数和高环境稳定性，是全无机无铅钙钛矿太阳能电池的一种潜在光吸收材料。然而，基于CsTiI₂Br制备的太阳能电池性能不佳，其低效率的原因仍不清楚。在此，通过时域密度泛函理论结合非绝热分子动力学方法研究了CsTiI₂Br（x = 0、2和6）中的热载流子弛豫过程。结果发现，CsTiI₂Br中热载流子的弛豫时间在2 - 3皮秒范围内，这表明在CsTiI₂Br/TiO界面10纳米内的热载流子在其能量完全损失之前能够被有效提取。载流子 - 声子非绝热耦合（NAC）分析表明，与CsTiBr和CsTiI相比，CsTiI₂Br中热电子弛豫时间更长源于其较弱的NAC强度。此外，电子 - 声子相互作用分析表明，热电子的弛豫主要来自分布在Ti - X键上的电子与Ti - X振动之间的耦合，而热空穴的弛豫可归因于分布在X原子上的电子与[TiI₂Br]畸变之间的耦合。模拟结果表明，基于热载流子能量损失，CsTiI₂Br作为光吸收层应优于CsTiBr和CsTiI，并且CsTiI₂Br中的热电子弛豫时间可通过调节I元素的比例来调整。
