Cheng Yuanhang, Liu Xixia, Guan Zhiqiang, Li Menglin, Zeng Zixin, Li Ho-Wa, Tsang Sai-Wing, Aberle Armin Gerhard, Lin Fen
Solar Energy Research Institute of Singapore, National University of Singapore, Singapore, 117574, Singapore.
Department of Materials Science and Engineering, College of Engineering, Peking University, Beijing, 100871, China.
Adv Mater. 2021 Jan;33(3):e2006170. doi: 10.1002/adma.202006170. Epub 2020 Dec 9.
Ion dissociation has been identified to determine the intrinsic stability of perovskite solar cells (PVSCs), but the underlying degradation mechanism is still elusive. Herein, by combining highly sensitive sub-bandgap external quantum efficiency (s-EQE) spectroscopy, impedance analysis, and theoretical calculations, the evolution of defect states in PVSCs during the degradation can be monitored. It is found that the degradation of PVSCs can be divided into three steps: 1) dissociation of ions from perovskite lattices, 2) migration of dissociated ions, and 3) consumption of I by reacting with metal electrode. Importantly, step (3) is found to be crucial as it will accelerate the first two steps and lead to continuous degradation. By replacing the metal with more chemically robust indium tin oxide (ITO), it is found that the dissociated ions under light soaking will only saturate at the perovskite/ITO interface. Importantly, the dissociated ions will subsequently restore to the corresponding vacancies under dark condition to heal the perovskite and photovoltaic performance. Such shuttling of mobile ions without consumption in the ITO-contact PVSCs results in harvesting-rest-recovery cycles in natural day/night operation. It is envisioned that the mechanism of the intrinsic perovskite material degradation reported here will lead to clearer research directions toward highly stable PVSCs.
离子解离已被确定为决定钙钛矿太阳能电池（PVSCs）本征稳定性的因素，但其潜在的降解机制仍不清楚。在此，通过结合高灵敏度的子带隙外部量子效率（s-EQE）光谱、阻抗分析和理论计算，可以监测PVSCs在降解过程中缺陷态的演变。研究发现，PVSCs的降解可分为三个步骤：1）离子从钙钛矿晶格中解离；2）解离离子的迁移；3）I与金属电极反应而消耗。重要的是，发现步骤（3）至关重要，因为它会加速前两个步骤并导致持续降解。通过用化学稳定性更高的氧化铟锡（ITO）替代金属，发现光浸泡下的解离离子只会在钙钛矿/ITO界面处饱和。重要的是，解离离子随后会在黑暗条件下恢复为相应的空位，从而修复钙钛矿和光伏性能。在ITO接触的PVSCs中，这种移动离子的穿梭而不消耗导致了在自然昼夜运行中的捕获-恢复-再恢复循环。可以预见，本文报道的本征钙钛矿材料降解机制将为高度稳定的PVSCs带来更清晰的研究方向。
