摘要/Abstract

本工作实验对比了可见光以及紫外光辐照下甲氨碘化铅(CH₃NH₃PbI₃即MAPbI₃)基钙钛矿太阳能电池器件性能及微结构演变特征差异. 结果表明可见光辐照下钙钛矿太阳能电池器件中MAPbI₃层发生降解的同时, 伴随着Au元素从金属电极一侧向MAPbI₃和电子传输层SnO₂的界面处迁移现象. 但相较于紫外光, 可见光辐照下器件中Au元素的迁移速率慢30倍左右. 这是由于器件电子传输层SnO₂具有较低的价带顶位置(–8.4 eV), 它吸收紫外光激发出强氧化性的空穴h⁺, 氧化碘离子I^–生成I原子. 而I原子会对金属电极层产生较大的破坏作用, 促进Au⁺离子的形成. 因此可见光辐照下, 尽管器件开路电压V_oc一直保持较高的数值, 但是Au元素的迁移以及钙钛矿层的分解, 会引起短路电流密度J_sc的快速降低. 本文为钙钛矿太阳能电池光照不稳定性的机理解释, 提供了全新的理论依据.
关键词: 钙钛矿太阳能电池, 光辐照, 迁移动力学, 电子显微学, 光降解
In recent years, the photoelectronic conversion efficiency (PCE) of organic-inorganic halide perovskite solar cell (PSC) devices has been improved greatly. However, these devices are not very stable, and it is hard to avoid the effect of visible or ultraviolet (UV) light on the performance decay of the organic-inorganic halide perovskite devices, and there is rare report on the evolution process of the microstructure of PSCs under the light illumination, let along discussing on the different degradation mechanism of PSCs between the UV and visible light soaking. To address these scientific issues, in this study, we compared the performance evolution of CH₃NH₃PbI₃ (MAPbI₃) based PSCs during the UV and visible light irradiation. The experimental results show that the perovskite layer has been photodegraded from MAPbI₃into an amorphous phase under the white light LED soaking. Meanwhile, the migration of Au element from the electrode into the interface between MAPbI₃ and SnO₂ layers can also be captured. As comparing the kinetics of redox reaction of Au, we found that the formation rate of Au nanoparticle mass in PSCs under UV light irradiation is almost 30 times higher than that under visible light illumination. Considering on the different characteristics of microstructure evolution in PSCs under the UV and visible light irradiation, and theoretically analyzing the energy level of each functional layers in the device, the results confirm that UV light is easy to be adsorbed by electron transportation layer (ETL) of SnO₂ to excite the electron-hole pairs, while the photo-excited holes have a low energy level of –8.4 eV, which could oxidize the iodide ions (I ^–) into atomic iodine (I atom). The I atoms would diffuse into the spiro-OMeTAD layer and metal electrode interface. Due to its strong oxidation property, the I atom would not only destroy the spiro-OMeTAD layer, but also oxidize the Au metal electrode into AuI, which accelerated the generation of Au⁺. However, under the illumination of visible light, it is hard to excite the electron-hole pairs in SnO₂, which prevents the damage on the functional interfaces, and the transportation energy barrier is unchanged. So, the open circuit voltage (V_oc) has a long-term photo-stability. However, the short-circuit current density (J_sc) decreased rapidly under visible light illumination, which is mostly ascribed to the changes of charge mobility resulting from the migration of Au element and photodecomposition of MAPbI₃ layer. All these results give a new insight to understand the photo-instability of PSC.
Key words: perovskite solar cell, light illumination, migration dynamics, electron microscopy, photo-degradation


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