Efficient and Stable Perovskite Solar Cells with a Superhydrophobic Two-Dimensional Capping Layer

A two-dimensional (2D) perovskite layer is considered to be a desirable defect passivation structure for the lifelong stability of perovskite solar cells (PSCs). However, the efficiency could be compromised behind the traditional PSCs. Herein, we solve this issue by employing a highly hydrophobic organic cation, 2-[4-(trifluoromethyl)phenyl]ethanamine (CF₃-PEA), to form a 2D (CF₃-PEA)₂PbI₄ to effectively passivate the 3D MAPbI₃ with fewer defects. The new 2D/3D-structured PSCs show reduced charge recombination, an elongated carrier lifetime, efficient charge generation and transport. Those excellent characters lead to a significant enhancement of the efficiency from 17.9% for pristine PSCs to 21.43% for 2D/3D PSCs. Benefiting from the high hydrophobicity of CF₃-PEA, the cells show remarkably improved stability by maintaining 83% of the original efficiency exposed to 80% R.H. and 50 °C for 600 h and 87% under 1 sun illumination for 600 h, which makes our PCSs among the most efficient and stable MAPbI3 solar cells.