Molecular Engineering of 2D Spacer Cations to Achieve Efficient and Stable 2D/3D Perovskite Solar Cells

Introducing 2D perovskite onto the surface of 3D perovskite could not only passivate the defects in 3D perovskite, but also protect the 3D perovskite from humidity invasion, which could improve the device stability. The choice of spacer cations in 2D perovskites directly influences the overall properties of the 2D layer, which is crucial to the efficiency and stability of devices. Herein, trifluoromethyl benzylamine is developed as the 2D spacer cation, and the effects of –CF 3 at different substitution positions on the surface morphology, carrier dynamics, and device performances are systematically investigated. Results show that the 3‐TFPMAI‐treated 2D/3D perovskite film shows smoother morphology, with fewer surface defects and less nonradiative recombination. Moreover, with a matched energy level, 3‐TFPMAI modification can accelerate hole extraction and hole transporting. The 3‐TFPMAI‐treated 2D/3D cell achieves a champion efficiency of 22.68%. What's more, the introduction of fluoride‐containing groups increases the hydrophobicity of the 2D layer, which effectively resists moisture erosion and greatly improves the long‐term and operational stability of the perovskite solar cells.