Cs0.15FA0.85PbI3/CsxFA1-xPbI3 Core/Shell Heterostructure for Highly Stable and Efficient Perovskite Solar Cells
Zijian Peng, Qi Wei, Hao Chen, Yawen Liu, Fei Wang, Xianyuan Jiang, Weiyan Liu, Wenjia Zhou, Shengjie Ling, Zhijun Ning
Abstract
Dissociation of organic molecules is one critical factor leading to degradation of perovskite solar cells. The much-improved thermal stability of formamidinium (FA) can significantly reduce molecular dissociation; however, FA-based perovskite suffers from high defect density, which affects efficiency and long-term stability. In this work, based on a precise ion-exchange reaction at the grain surface, we fabricate a Cs0.15FA0.85PbI3/CsxFA1-xPbI3 heterostructure with a Cs-rich CsxFA1-xPbI3 quasi-shell structure. The Cs-rich inorganic structure on the perovskite surface increases defect formation energy and reduces defect density, leading to a power conversion efficiency of 20.7%. The encapsulated device maintains 95% of its initial efficiency after 1,000 h of continuous operation, corresponding to a calculated lifetime approaching 2 years. The device can operate at 60°C for 250 h and at 85°C for over 3,000 min, which is one of the best operational stabilities for CsxFA1-xPbI3-based devices.