Bilayer 2D-3D Perovskite Heterostructures for Efficient and Stable Solar Cells.

With a stacking-layered architecture, the bilayer two-dimensional-three-dimensional (2D-3D) perovskite heterostructure (PHS) not only eliminates surface defects but also protects the 3D perovskite matrix from external stimuli. However, these bilayer 2D-3D PHSs suffer from impaired interfacial charge carrier transport due to the relatively insulating 2D perovskite fragments with a random phase distribution. Over the past decade, substantial efforts have been devoted to pioneering molecular and structural designs of the 2D perovskite interlayers for improving their charge carrier mobility, which enables state-of-the-art perovskite solar cells with high power conversion efficiency and exceptional operational stability. Herein, this review offers a comprehensive and up-to-date overview on the recent progress of bilayer 2D-3D PHSs, encompassing advancements on spacer cation engineering, interfacial charge carrier modification, advanced deposition protocols, and characterization techniques. Then, the evolutionary trajectory of bilayer 2D-3D PHSs is outlined by summarizing its mainstream development trends, followed by a perspective discussion about its future research opportunities toward efficient and durable perovskite solar cells.