Surface Terminated 3D/2D Heterojunction Enables Efficient and Stable Perovskite Solar Cells

Abstract Bilayer 3D/2D heterojunction perovskite solar cells (PSCs) have attracted increasing interest due to great advantages of high power conversion efficiency (PCE) and ultrastability. Previous studies are mostly focused on addressing the issue of poor charge transport originated from the spacer cations or random phase distribution of 2D perovskite in 3D/2D heterojunction. However, the carrier recombination at the surface of 2D layer is often ignored. Herein, a novel strategy of passivating 2D perovskite in 3D/2D heterojunction with a thin surface termination layer (STL) is proposed. It demonstrates that surface defects of 2D perovskite are terminated by the molecule of 2‐amino‐5‐mercapto‐1,3,4‐thiadiazole through multi‐site interaction, leading to the significant suppression of non‐radiative recombination and considerable improvement of hole transport with the well‐aligned energy band simultaneously. As a result, the PSCs with the constructed 3D/2D/STL structure processed in air have achieved a champion PCE of 25.09% with high open‐circuit voltage of 1.211 V (the voltage deficient of 0.349 V). The unencapsulated devices retain exceeding 90% of the initial PCE after storing in air for 1008 h or under illumination in N 2 for 504 h. This work opens up an important, but unnoticed topic of defect passivation of 2D perovskite for 3D/2D heterojunction PSCs.