Spacer Cations: Molecular Switches for 2D and 2D/3D Perovskite Photovoltaics

Abstract

Over the past decade, perovskite solar cells (PSCs) have advanced rapidly, with power conversion efficiencies (PCE) exceeding 27%. Nevertheless, conventional three-dimensional (3D) perovskites still face serious stability challenges，posing a key obstacle to commercialization. Introducing bulky organic spacer cations into 3D perovskites to construct two-dimensional (2D) perovskites can markedly enhance stability. As Molecular Switches in 2D and 2D/3D PSCs, spacer cations enable precise control over crystal structure, optoelectronic properties, and stability. This review systematically outlines the classes of spacer cations and the principles guiding their design, provides an in-depth analysis of the mechanisms by which they regulate perovskite properties, summarizes advances in 2D and 2D/3D PSCs enabled by spacer-cation engineering, and highlights core challenges and future directions, thereby offering theoretical support for the development of efficient and stable perovskite photovoltaic devices.