Difluorine‐Substituted Molecule‐Based Low‐Dimensional Structure for Highly Stable Tin Perovskite Solar Cells

Despite tin perovskite showing excellent optoelectronic properties such as ideal bandgap and high carrier mobility, the intrinsic instability of tin perovskite due to the reaction with water and oxygen that significantly shadows its application. Herein, a molecule substituted with two fluorine atoms for the construction of low‐dimensional tin perovskite is explored. Tin perovskite film based on this molecule shows much enhanced hydrophobicity, bringing much enhanced stability in atmosphere. The unencapsulated device can be kept over 200 h in atmospheric environment. In comparison to the instantaneous degradation of device performance for traditional 3D solar cells, no obvious degradation of device efficiency is observed under continuous operation in atmosphere without encapsulation over 10 h. Furthermore, the low‐dimensional perovskite film exhibits a unique two‐layer structure that can effectively passivate defects of the tin perovskite film. Accordingly, the power conversion efficiency (PCE) of Sn‐perovskite solar cells realizes a remarkable enhancement by a factor of 45% and yields a PCE of 8.38%. This work indicates that molecular design of low‐dimensional structure is a promising approach to improve the stability of tin perovskite.