Fabrication Strategy for Efficient 2D/3D Perovskite Solar Cells Enabled by Diffusion Passivation and Strain Compensation

Lattice matching and passivation are generally seen as the main beneficial effects in 2D/3D perovskite heterostructured solar cells, but the understanding of the mechanisms involved is still incomplete. In this work, it is shown that 2D/3D heterostructure are unstable under common thermal processing conditions, caused by the lattice expansion of strained 2D perovskite. Therefore an innovative fabrication technology involving a compressively strained PEA 2 PbI 4 layer is proposed to compensate the internal tensile strain and stabilize the 2D/3D heterostructure. Moreover, a small amount of PEA + diffusing into the grain boundaries of 3D perovskite forms 2D perovskite and passivates the defects there. Combining the effects of strain compensation and diffusion passivation, the stabilized 2D/3D perovskite solar cells deliver a reproducible and robust laboratory power conversion efficiency (PCE) of 21.31% for the p‐i‐n type devices, along with a high V OC of 1.18 V. A certified PCE of 20.22% is confirmed by an independent national metrology institute.